The medieval period is vast. Temporally, it extends from at least the time of St. Augustine (d. 430) until, perhaps, the time of John of St. Thomas, also called John Poinsot (d. 1644). Spatially, it extends from Spain and Portugal in the West to China in the East, from Germany in the North to North Africa in the South. Linguistically, it includes Latin, Arabic, Hebrew, Sanskrit, Chinese, and some early vernacular European languages like Italian. Religiously, it includes Christianity, Islam, Judaism, Hinduism, Buddhism, and other pagan religions. This article will focus on medieval philosophy, conducted in Latin by Western Christian authors in the High Medieval period (ca. 1225–1308). This period was marked by the confluence of a rich tradition of theological speculation coming especially from St. Augustine, the tradition of the Benedictine order and Cathedral schools, an influx of new works by Aristotle as well as Jewish and Muslim philosophers, the new Mendicant orders of the Franciscans and Dominicans, and the University. This article will focus on the major philosophers of the time as well as many of the main debates that occurred in the period. Additionally, it will explain some of the historical factors that led to the rise of the aforementioned theological speculation. Despite its narrowness in comparison to all medieval philosophy, this article will be necessarily general. Each of the topics covered here is covered in more detail in individual articles which readers are encouraged to explore.

I. Historical Context

During this period, philosophical and theological thought was conditioned by five particularly important historical considerations: the new mendicant orders, the foundation of the university, the influx of new texts, the Condemnations of 1270 and 1277, and the major figures of the period.

Religious Orders

Without a doubt, the major western religious order prior to the thirteenth century was the Order of St. Benedict. The Benedictine way of life was founded as “a school for the Lord’s service” (Rule of St. Benedict, prol., v. 45). Though the sixth century Rule is silent about education, this is clearly envisioned as being part of the life of the monastery. Given that the Rule includes provisions for receiving the children of nobles and of the poor (ch. 59), and that it instructs every monk to engage in reading (ch. 48), one would conclude that the boys who were received into monastic life must have been taught to read. During the Carolingian Renaissance of the eighth century, Charlemagne called upon Benedictine monks, especially St. Alcuin of York, to lead a revival in education. In his Dialogue on True Philosophy, St. Alcuin identifies seven stages of philosophy which correspond to the seven liberal arts: grammar, rhetoric, dialectic, arithmetic, geometry, music, and astronomy. He also distinguishes philosophy proper as reasoning toward first principles. The Benedictine tradition of education continued through to the great monks St. Anselm and St. Bernard, the latter of whom belonged to the more contemplative Cistercian development from the Benedictine order (Leclerq, The Love of Learning and the Desire for God).

Although not exclusively so, the education of the monk tended to have a practical orientation. Education was for the sake of drawing closer to Christ, which meant that more speculative questions did not always have to be raised. This orientation toward Christ also affected the texts that were chosen. Monastic theology tended to focus on Sacred Scripture and glosses and commentaries on the same. Secular learning was not entirely shunned, but its dangers were readily acknowledged.

The beginning of the thirteenth century saw the rise of two new orders: the Order of Friars Minor (following the inspiration of St. Francis) and the Order of Preachers (following the inspiration of St. Dominic). Both orders were founded on the principle of poverty embraced for the sake of Christ and for the purpose of proclaiming the Gospel. The need for appropriate education necessarily followed from this, for a good preacher must know how to speak well and how to read the Bible well. As a result, both mendicant orders established their own schools (studia) for lower education, and they also gravitated toward the Universities. Despite their youth, both orders rose to prominence in education. In fact, almost all the influential philosophers of this time came from these orders.

As these orders became more prominent, controversies, both internal and external, began to arise. For the Franciscans, there was a controversy within the order over whether education was compatible with the charism of the order. Some Franciscans, notably an early Minister General of the Order, John of Parma (ca. 1208–1289), thought that the new orders were the “spiritual men” who would lead history into the third and final period of history prophesized by Joachim of Fiore (d. 1204). Education was thought to be in conflict with this role and therefore to be rejected. Both the Franciscans and the Dominicans faced objections from the secular (i.e., diocesan) masters at the Universities. The more extreme objections contended that the evangelical poverty of the orders was, in fact, so contrary to the Gospel that the orders should not even exist. These accusations came especially from William of Saint-Amour, and they were notably countered by the Franciscan St. Bonaventure (ca. 1221–1274) and the Dominican St. Thomas Aquinas (1224/5–1274) (Hughes, “Bonaventure’s Defense of the Mendicants”; Torrell, Thomas Aquinas, 92–114). The other major controversy centered on a difference between mendicant and secular education, namely that mendicant education was briefer than secular education. Thus, the seculars objected that the mendicant theologians were unqualified to hold chairs of theology at the University (Mulchahey, First the Bow is Bent in Study; Roest, A History of Franciscan Education (c. 1210-1517)).

The Foundation of the University

Before the thirteenth century, education was primarily conducted at monasteries, cathedral schools, or on an ad hoc basis with a willing student sitting before the feet of a master for instruction. St. Anselm is a primary example of monastic education. His intellectually rigorous inquiry went well beyond study for the sake of devotion or liturgy alone, yet his work took place within the monastery. Cathedral schools were places where teachers offered courses going beyond the customary sequence of grammar, composition, and rhetoric, requiring their students to investigate logic and natural philosophy. The novelty of this course of study soon made the cathedral schools enviable destinations for students. Moreover, as students came from far and wide to places like Paris, some teachers set up their own ad hoc schools. The most famous of these schools is the one at Saint-Victor, from which came the great work of Hugh of Saint-Victor and Richard of Saint-Victor. The great proliferation of schools at this time made a sort of centralization and coordination a practical necessity (see Marrone, “The Rise of the Universities”).

In 1200, King Philip of France founded the University of Paris. In doing so, he realized the vision of St. Augustine laid out in De doctrina Christiana. St. Augustine’s life was riddled with theological battles with the Manicheans and Pelagians. Members of both heretical sects claimed that their positions were properly biblical, which led St. Augustine to the conclusion that a proper education was necessary in order to read Sacred Scripture well. Thus, he outlined a course of studies in the liberal arts, philosophy, and theology that would yield educated and orthodox men. The University of Paris, with just such a goal in mind, included four faculties: arts, medicine, canon and civil law, and theology The lower faculty was the arts faculty, which conducted the philosophical education. As we will see more in the next section on the influx of texts, the texts for this course underwent serious revision during this time period. At the beginning, the texts for this faculty included, among others, the works of St. Augustine, Boethius, Cicero, Isidore of Seville, and St. Anselm. Thus, we rightly say that the philosophical education in this period was primarily indebted to Platonic, or at least Neo-Platonic, philosophy (Chenu, Man, Nature, and Society in the 12th Century, 49–98). In 1255, however, and despite controversy which will be noted in the next section, the official curriculum of the arts course was changed to include all of Aristotle’s philosophical works. (Chartularium Universitatis Parisiensis, vol. 1, n. 246).

After completing the arts course, students could proceed to the faculties of medicine, law (canon or civil), or theology. The theology faculty is the most important for our purposes. The education received in the theology faculty was a product of the scholastic developments of the twelfth century. At that time, the masters began asking and responding to more speculative questions about the biblical texts on which they were lecturing. These questions soon became so involved that they had to be separated from the lecture and became their own activity. This separation led to such works as Peter Lombard’s (d. 1160) Book of Sentences, which consisted of a four-book series of theological topics ordered systematically. For each topic, he gathered many of the sayings of the Fathers of the Church and attempted to bring all their positions into harmony, advocating for a certain position on some occasions. Thanks to the Franciscan Master Alexander of Hales (ca. 1185–1245), the Book of Sentences became the standard theology textbook in the thirteenth century. Students in the theology course had to listen to several years of lectures on Sacred Scripture and other theological works, including the Book of Sentences, participate in disputations, and lecture on Sacred Scripture and the Book of Sentences before they could be admitted to the faculty themselves as Magister Sacrae Paginae (Master of the Sacred Page) (Chenu, Nature, Man, and Society in the Twelfth Century, 270–309; Noone, “Scholasticism”).

Thus, the education of a Magister Sacrae Paginae included many years of philosophical and theological study, culminating in the ability to read Sacred Scripture in an orthodox manner. The University produced several types of literature which illustrate the emphasis on philosophical reflection characteristic of this period. First, we find commentaries on Lombard’s Sentences, which treat philosophical topics in various places where such speculation becomes necessary for the theological topic. Second, we find disputed questions which would have been part of the ordinary classroom disputation for the masters. The master would propose a question, then two advanced students would provide long series of arguments pro and con. Then, on a separate day, the master would offer his own answer to the question along with a reply to every argument from the advanced students who disagreed with his position. These disputations were written down, and, ideally, edited by the master before being published by the University bookstore. Third, we find quodlibetal questions (quaestiones de quodlibet, i.e., questions on anything whatsoever), which emerged out of the University tradition of setting aside two days a year (one in Advent and one in Lent) for the entire community, including those outside the university, to ask questions of the master sitting for quodlibetal questioning. Fourth, we find commentaries on Aristotle. Fifth, we find independent philosophical works, such as St. Thomas Aquinas’s On Being and Essence. Lastly and most importantly, we have commentaries on Sacred Scripture. These commentaries were the height of a master’s work and frequently reveal his most mature thought.

The Influx of New Texts

There was a tremendous influx of texts at this time. Latin readers had had access to a group of texts known as the “old logic” (logica vetus), which consisted of Aristotle’s Categories and De interpretatione (Perihermenias), Porphyry’s Isagoge (Introduction to Aristotle’s Categories), Boethius’s commentaries on these three works, Boethius’s Topical Differences, and Cicero’s Topics. Beginning about 1150, a large translation project began in the city of Toledo in Muslim Spain. Dominicus Gundissalinus (fl. 1150–1190) and others translated the works of Aristotle, Avicenna, Averroes, and others. Thus, whereas prior generations’ access to philosophical texts was mostly restricted to logic, now the full gamut of philosophical areas was available: physics, psychology, metaphysics, ethics, and politics. Dominicus also introduced the practice of providing a rationale for dividing the sciences in various ways through his work On the Division of Philosophy.

The teachings found in these newly translated texts were received with mixed enthusiasm. On the one hand, the theories found in Aristotle and others were intellectually robust and seemed compatible with the Christian faith in many ways. On the other hand, some of the principles of Aristotle seemed to lead to unacceptable conclusions. St. Bonaventure in his Collations on the Gifts of the Holy Spirit (1268) identifies three errors associated with these texts. They err in teaching that the world is eternal, that everything happens by fatal necessity, and that there is numerically one human intellect (collation 8, n. 16. Cf. Bonaventure, Collations on the Ten Commandments, collation 2, n. 24). In his later Collations on the Six Days of Creation, St. Bonaventure also described erroneous ideas related to exemplarity, divine providence, and the arrangement of the world (collation 6, nn. 3–4). Concerns about the teachings of Aristotle, like the ones later outlined by St. Bonaventure, resulted in Aristotle’s works being condemned. In 1210, the Archbishop of Paris, Peter of Corbolio, declared that neither “the books of Aristotle on natural philosophy nor commentaries are to be lectured on publicly or privately” (Chartularium Universitatis Parisiensis, vol. 1, n. 11). In 1215, this condemnation was reaffirmed by a Cardinal Robert, who further specified that “the books of Aristotle on metaphysics and on natural philosophy, nor summaries (summe) on the same are to be lectured upon” (Chartularium Universitatis Parisiensis, vol. 1, n. 20). Again in 1231, Pope Gregory IX reiterated the condemnation of teaching Aristotle’s works on metaphysics and natural philosophy (Chartularium Universitatis Parisiensis, vol. 1, n. 87).

While these condemnations forbade the teaching of Aristotle, it is clear that the masters continued to read him and that they actively drew upon his natural and metaphysical texts in their own writings. The most blatant case is the Franciscan Jean de la Rochelle (d. 1245), who draws on Aristotle heavily and by name in his Summa de anima. By 1255, it was clear that not only could Aristotle’s texts not be kept from the students but that the good to be found in them outweighed the bad. Thus, it was then declared that Aristotle’s works were a mandatory and central part of the arts course (Chartularium Universitatis Parisiensis, vol. 1, n. 246). Importantly, the list of Aristotle’s works includes the Liber de causis (Book of Causes). This work is not by Aristotle, but instead by a medieval author writing in Arabic who was inspired by the Neo-Platonic work Elements of Theology by Proclus. Although St. Thomas Aquinas tells us in the preface of his 1272 commentary on the Liber de causis that the work is surely not by Aristotle, the fact that it was thought to be Aristotle’s means that the Platonic reasoning of the book was thought to be in harmony with Aristotle’s other texts (Porro, “The University of Paris in the thirteenth century Proclus and the Liber de causis”). Thus, while it was at one time in vogue to oppose Platonism and Aristotelianism in this period, the thinkers at this time would not have seen such an opposition.

Along with Aristotle, the importance of the works of Muslim philosophers Avicenna (Ibn Sina, d. 1031) and Averroes (Ibn Rushd, d. 1198) must be noted. Avicenna wrote many complete works of philosophy, only one of which was translated into Latin: The Book of the Healing. This text is, by Avicenna’s own admission, the most Aristotelian of Avicenna’s philosophical works, and it seeks to draw together the Platonic and Aristotelian strands of thought that came down to him. The section of the text on the soul was especially influential during the Latin Middle Ages, as were certain parts of the section on metaphysics (Amos Bertolacci, “The Reception of Avicenna in Latin Medieval Culture”). Averroes, who comes to be known as “the Commentator,” was valuable to authors in this time period because of his “Long commentaries” on Aristotle’s works. These line-by-line commentaries explain Aristotle’s dense and obscure texts with tremendous clarity. Despite his clarity, the works of Averroes had special dangers attached to them. For one, it was Averroes who introduced the idea that there is numerically one human intellect as the authoritative reading of Aristotle to the Latins. For another, the Latins were able to reconstruct Averroes’s teaching that philosophy is higher than theology because philosophy begins with first principles that are known in themselves whereas theology begins from revelation, which is not known in themselves and can be denied. Thus, when St. Bonaventure and others speak of the errors that come from Aristotle and the philosophers, they are speaking of a movement within the University that seems to have been present as early as 1254, when St. Bonaventure delivered his inception lecture as a master, and came to a head in the 1260s and 1270s. Scholars have come to call this movement “Latin Averroism” or “Radical Aristotelianism” (Van Steenberghen, Thomas Aquinas and Radical Aristotelianism; Piolata, “Bonaventure’s Collationes in Hexaemeron and Radical Aristotelianism”).

The Condemnations of 1270 and 1277

In the wake of Latin Averroism, the bishop of Paris, Stephen Tempier, sought to curtail the errors being taught at the university. On December 10, 1270, he issued a condemnation of 13 propositions and on March 7, 1277, he issued a condemnation of 219 – 220 propositions (Chartularium Universitatis Parisiensis, vol. 1, nn. 432 and 473). Among the propositions condemned in 1270 were the claims that “The intellect of all men is numerically one and the same;” “The world is eternal;” “Human acts are not ruled by God’s providence;” and “Man’s will wills or chooses from necessity.” This last proposition is particularly worth noting because it plays a decisive role in shifting the way that authors in our period understand human nature and ethics. Earlier authors like St. Bonaventure and St. Thomas give pride of place to the intellect as guide of our actions. A generation later, Bl. John Duns Scotus (d. 1308) would argue that because the human will never wills or chooses by necessity, we can do the opposite action from the action we are currently doing, or at least refrain from performing any action. All these thinkers emphasize the importance of both intellect and will in our moral decision making and acting. Nonetheless, the condemnation of 1270 resulted in a shift of emphasis from intellect to will.

Major Authors of the Period

The time period ca. 1225–1308 can be divided into three smaller periods, each with its own set of authors attempting an integration of the texts of Aristotle, Avicenna, and Averroes. The first major attempt at integration took place roughly before 1255. The major theologians of this sub-period include the Franciscan masters Alexander of Hales, Jean de la Rochelle, Richard Rufus of Cornwall (fl. 1231–1256), and Roger Bacon (d. 1292), the Dominican master St. Albertus Magnus (1200–1280) and the secular masters William of Auvergne (d. 1231), Robert Grosseteste (d. 1253), and William of Auvergne (d. 1249). As a general rule, they accept Avicenna’s account of the soul and hold an epistemological theory of divine illumination. The second sub-period is from about 1255–1274, and it includes the towering figures of St. Bonaventure and St. Thomas Aquinas. Notably, it also includes the secular arts masters Siger of Brabant (d. after 1282) and Boethius of Dacia (fl. 1270–1280), who are the major supporters of the positions associated with Latin Averroism. The final sub-period, after the death of St. Bonaventure and St. Thomas in 1274, includes the highly influential secular master Henry of Ghent, who taught at the University of Paris from 1279–1292 and died in 1293, Franciscan masters Richard of Mediavilla (d. 1302), Peter John Olivi (d. 1298), John Pecham (d. 1292), Matthew of Aquasparta (d. 1302), Bl. John Duns Scotus (d. 1308), and Peter Auriol (d. 1322), the Dominican masters John of Paris (or Quidort, d. 1306), the Augustinian masters Giles of Rome (d. 1316) and James of Viterbo (d. 1307/8), and secular master Godfrey of Fontaines (d. 1316). Not all of these figures will appear in what follows, but it is helpful to know some of their names.

II. Faith and Reason

There is nearly universal agreement in the medieval period that faith and reason (theology and philosophy) are harmonious. St. Thomas Aquinas’s account of their relationship in Commentary on the De Trinitate of Boethius, q. 2, a. 3 (ca. 1257–1260) is representative of the view. He says that the gifts of grace are added to nature in such a way that nature is perfected, not destroyed. So, when the light of faith is given to us by God, it does not destroy our natural light of reason. If the proper use of each light results in contrary conclusions, then one of them must be false. And since both lights are from God, God would be the author of falsity. Thus, the lights and the areas of study that are founded upon them cannot contradict one another. The natural light of reason falls short of all the things that are known by faith, such as the Trinity and the Incarnation, but nothing of philosophy can contradict these. When properly used, philosophy even discovers certain preambles of faith (e.g., that God exists, is one, etc.). Additionally, philosophy can supply certain likenesses of things that are of faith, such as St. Augustine’s use of the memory, understanding, and will of the mind as likenesses of God’s unity and trinity. Finally, philosophy can be used to resist claims against the faith either by showing that such claims are false by showing that the opposite is true, or at least by showing that such claims are not necessary. He includes the latter because there are some truths, such as the Trinity and Incarnation, that reason cannot definitively prove. So, claims against them cannot be definitively proven false, but they can be shown to be not necessarily true.

St. Thomas ends his question with two warnings against the use of philosophy. First, false claims taken from philosophy, since they are false, are actually abuses of philosophy and must not be used as the basis for theological reasoning. Second, we must not value philosophy so much that we subordinate theology to philosophy and declare that everything pertaining to faith falls under philosophy.

III. Metaphysics

Science of Being

Medieval philosophers take the notion of a science (scientia) seriously. The return of Aristotle’s Posterior Analytics is a major factor in this movement. In that work, Aristotle lays out the conditions for self-evident knowledge (per se notum), proceeding from first principles to necessary conclusions and then to a discussion of how to obtain first principles. Here, the question is not merely whether the structure of the argument yields a valid conclusion, but also whether the argument has truth and demonstrative soundness. To use terms from later scholasticism, the issue is not formal logic but material logic, specifically demonstrative matters. Thinkers during the Latin Middle Ages took these requirements very seriously and attempt to apply them to every inquiry, including theology. The Islamic sources utilized by Latin thinkers provided an important impetus for the prioritizing of scientific demonstration, as they would also influence the inclusion of the Aristotelian Rhetoric and Poetics among the logical works (Henrik Lagerlund, “Assimilation of Aristotelian and Arabic Logic up until the Later 13th Century,” Black, Logic and Aristotle’s Rhetoric and Poetics in Medieval Arabic Philosophy).

Although they do not all understand the subject in precisely the same way, the Scholastics agree that the subject of metaphysics is being insofar as it is being, not God. Bonaventure argues that the study of being as being is the study of the essences of things (Itinerarium, c. 3, n. 6), that is, the abstracted forms, as opposed to natural philosophy, which studies concrete forms, and mathematics, which studies separated forms (Seven Gifts of the Holy Spirit, coll. 4, n. 9). In his Collations on the Six Days of Creation, he distinguishes two types of essence (coll. 1, nn. 10–13). The first sort of essence is from itself, according to itself, and because of itself. The second sort of essence is from another, according to another, and because of another. Metaphysics begins by studying the second sort of essence and leads to the study of the first sort of essence as the principle, exemplar, and final end of the second sort of essence. Because of these three, he declares “this is our whole metaphysics: emanation, exemplarity, and consummation, namely, to be illuminated by the spiritual rays and drawn back to the highest being” (Collations on the Six Days of Creation, coll. 1, n. 17). Of these tasks, he ranks the study of emanation highest and even declares that only those who undertake such an investigation are true metaphysicians.

Aquinas interprets the study of being as being as the study of being in general (ens commune), especially including the discovery of the principle by which beings actually exist, which he calls the act of being (actus essendi). In his Commentary on the De Trinitate of Boethius, q. 5, a. 3, St. Thomas argues that the subject of metaphysics is discovered by a negative judgment which he calls “separation.” This judgment consists in the claim that one thing can exist without another and especially that being (and certain aspects of it) can exist separately from matter. He expands upon this judgment in a. 4 when he specifies that metaphysics studies those aspects of reality that do not exist in matter and in motion by nature, but are sometimes found with them, such as being, substance, potency and act. And since it falls to a science to study not only its subject matter but the cause of its subject matter, metaphysics also studies God and separate substances (i.e., angels), which by their nature do not exist in matter and motion in such a way that they could never be in matter or motion. It is worth noting that this overly brief account of the subject of metaphysics is controversial among followers of Aquinas. Whereas this interpretation holds that the mere possibility of an immaterial being is enough to begin the study of metaphysics, there is another school of thought which holds that the science of metaphysics can only begin once the reality of an immaterial being has been proven, which occurs at the end of natural philosophy (see Ralph McInerny, Praeambula Fidei, 169–187).

John Duns Scotus holds that metaphysics is the study of being insofar as it is being. He did so for two reasons: out of agreement with Avicenna’s argument that God’s existence is proven in metaphysics (which could not be if God were the subject since no science proves the existence of its subject); and because being is common to everything considered in metaphysics (Questions on Aristotle’s Metaphysics VI, q. 4, n. 1). Both reasons are important for Scotus. The latter is especially important because the subject matter of metaphysics needs to be broad enough to cover everything treated in metaphysics. Being must be the subject because, in its broadest sense, it means whatever does not include a contradiction. So for Scotus, anything that does not include a contradiction, including God, angels, and substances, is part of the subject of metaphysics (Quodlibet q. 3, nn. 6–9). God does hold a special place in metaphysical investigation for Scotus because he is the being and subject par excellence, and all other beings depend upon him (Questions on Aristotle’s Metaphysics I, q. 1, nn. 130–36). But if the metaphysician only considered God’s existence and nature as it was demonstrated by the natural philosopher, then he would only know God insofar as he is the first mover (Questions on Aristotle’s Metaphysics VI, q. 4, n. 5). Such knowledge of God would not show that God is the primary being. Just as it does not follow that something is the primary black and the source of all other blacknesses and therefore the primary color, so it does not follow that the primary mover is necessarily the primary being. (See King, “Scotus on Metaphysics.”)

Analogy and Univocity of Being

Mention of Scotus’s claim that being is said in many ways brings up a hotly debated topic: the meaning of the term “being.” As a prelude to this debate, we must understand the distinction between univocal, equivocal, and analogical uses of terms. Although William of Auxerre identifies five modes of univocity (Summa aurea I.6.2), the standard account during this time period involves only one mode of univocity, drawn from Aristotle (Categories, c. 1; Posterior Analytics II, c. 14; Metaphysics IV, c. 2;). A term is used univocally when the same term has the same meaning each time it is used. The term “dog” is used univocally when we say, “Fido is a dog,” and “Spike is a dog.” A term is used equivocally when the same term has different meanings each time it is used. The term “base” is used equivocally when we say, “Pearl Harbor is a base” and “Baking soda (or sodium bicarbonate) is a base.”

Terms are used analogically when there is an inherent sameness and difference in each use of the term (see Clarke, The One and the Many, 44–52, and Ramirez, De analogia, 4 vols.). One type of analogy is called analogy of extrinsic attribution. In this sort of analogy, one of the subjects, called the primary analogate, receives the analogous term primarily and properly. The other subjects, called the secondary analogates, receive the analogous term secondarily and only because of some relation to the primary analogate. The usual example is the term “healthy.” We can say “Man is healthy,” “Food is healthy,” and “A blood test is healthy.” Health in man is the primary analogate because properly speaking, only the man can be healthy. Food can be called healthy because it causes the man to be healthy, and a blood test can be called healthy because it is a sign that the man is healthy. If the blood test is not healthy, we don’t take it to the hematologist. Instead, we treat the man.

The other main type of analogy is what Bonaventure calls an agreement of two to two (Commentary on the Sentences I, d. 1, a. 3, q. 1 and d. 3, p. 1, q. 2, ad 3) and what we usually call, following Cardinal Cajetan (Thomas de Vio, 1469–1534), analogy of proper proportionality (On the analogy of names, c. 3). In this sort of analogy, each of the analogates receives the analogous term properly and because of something proper to it. Unlike the blood test, which is not itself healthy, in the case of the analogy of proper proportionality, each analogate really is what the analogous term claims. Thus, we can say, “God knows,” “St. Michael the Archangel knows,” “A man knows,” “A worm knows.” In each case, each of these subjects really does know. However, the predicate “knows” does not mean precisely the same thing in each case since divine knowledge, angelic knowledge, human knowledge, and non-rational animal knowledge are distinct ways of knowing. God knows perfectly and simply by knowing himself. Angelic knowledge is purely intellectual and not discursive. Human knowledge arises from the external and internal senses, becomes intellectual, and is marked by rational discursivity. Non-rational animal knowledge is restricted to sense knowledge. Yet, these various kinds of knowledge are not equivocal because each entails real cognition. Thus, when the term “knows” is predicated of God, St. Michael, a man, and a worm, it is predicated of each in the way proper to it. So, “God knows” entails “God knows in a divine way,” and “St. Michael knows” entails “St. Michael knows in an angelic way.” The sameness and difference are built into the term itself.

An interesting question arises when we ask about the term “being.” When we say, “God is,” “St. Michael is,” and “A man is,” how is the verb “to be” being used? This question is especially urgent because it involves God. Earlier authors such as William of Auxerre argue that terms said of God and creatures, such as “just,” are equivocal in the sense that there cannot be a genus “just” under which both God and creature fall. Yet, these terms are univocal insofar as both divine and human justice agree in their effects of rendering what is due to each (Summa aurea I.5.3). Alexander of Hales argues that terms can be said of God and creatures according to priority and posteriority. Thus, a term like “person” has single, common intelligible content (ratio), but that ratio is not applied to God and creatures commonly, that is, univocally. God is person in a prior way to a creature, who is person in a posterior way (Glossa in I Sent., d. 25, n. 1d). Alexander’s solution is an example of the so-called “threefold way” (triplex via) of Pseudo-Dionysius (fl. ca. 500). Since God is the cause of all beings, we attribute to him everything that we attribute to beings. But since God surpasses all beings, we have to deny what we just attributed to him, lest we begin to think that he is a creature like us. Finally, we recognize that denials or negations are not the opposites of the affirmations, but attributions beyond every assertion. For example, we should say that God is good. But since God is not good in the same way that a dog or an ice cream cone are good, we have to negate “good” from God. But when we negate “good” we are not saying that God is evil or bad, we are saying that he is supremely and eminently good. The negation leads us to a recognition of God’s superabundance (See Dionysius, The Mystical Theology, n. 2).

Thomas Aquinas argues that “being” is said analogously in a way that combines the analogies of extrinsic attribution and proper proportionality. “God is” and “A man is” are analogous by proper proportionality because each one really exists and exists in the way proper to it. God exists divinely and a man exists humanly. Yet, the existence of each is not otherwise unrelated. God’s existence is uncaused and unlimited, whereas the man’s is caused and limited. So, existence or being is said of God primarily and of the man in a secondary and derived way. By articulating the analogy of being this way, Aquinas avoids anthropomorphizing God by univocity, thoroughly disconnects God from us by equivocity, and avoids the pantheistic claim that a creature’s existence or attributes are really just God or part of God. In this view, God remains transcendent but not separated from creation.{1}

Scotus argues that being, especially as applied to God, is both analogical and univocal: “Not only is God conceived in a concept analogous to the concept of a creature, namely, which is entirely other from that which is said of a creature, but in a certain concept univocal to him and a creature” (Ordinatio I, d. 3, p. 1, qq. 1–2, n. 26). For Scotus, a univocal concept of God and creatures is necessary because only univocal terms safeguard the validity of a syllogism used to reason philosophically about God. If when we said “All men are mortal. Socrates is a man. Therefore, Socrates is mortal” the term man meant something different in the first sentence and in the second sentence, then we would have committed the fallacy of equivocation, and our reasoning would come to nothing. Similarly, if the term being changes meaning when we argue to God’s existence, then our reasoning about God would come to nothing (Ordinatio I, d. 3, p. 1, qq. 1–2, n. 26). However, not all univocity is the same for Scotus. He distinguishes between “complete univocity” and “diminished univocity” (Ordinatio prol., p. 5, qq. 1–2, n. 366; Questions on Books II and III of Aristotle’s De anima, q. 1, n. 13). Complete univocity holds when there is a likeness in form and in the form’s the mode of being, and diminished univocity holds when there is a likeness in form but the mode of being of the form is different. He uses the example of a house. There is complete univocity between two actually existing houses since they are both houses and exist in the same manner. There is diminished univocity between a house existing in the mind and the house outside the mind which is patterned off of the house in the mind. Thus, since God and creatures are really diverse from each other, the univocity of being between them must be a diminished univocity (Ordinatio I, d. 8, p. 1, q. 3, n. 82). In fact, it is precisely the diminished sort of univocity that allows “being” which allows us to make a comparison between any two things, including between God and creatures.

Scotus argues that, although analogy is a weaker sort of unity than univocity, nothing prevents something from having both sorts of unity. He uses the example of genus and species. Plato and Socrates agree in genus (animal) and in species (man), and so they have an agreement in two distinct unities. We should note that the genus animal is measuring the species man but man is not measuring or governing animal. Thus, man depends on animal but not vice versa, and animal is attributed to man. Attribution, as we saw above, is a sort of analogy, which means that even though there is inequality of the character of animal in the genus and in the species man, what it is to be animal is the same in both. The same holds true of the term “being” in God and creatures since God is the cause and measure of creatures (Ordinatio I, d. 8, p. 1, q. 3, n. 83). Still, the positions of Scotus and Aquinas are not identical. There are still serious disputes between them, but I offer these few nuances to Scotus’s theory of univocity and analogy to show that their theories are not completely diverse and opposed (Smith, “The Analogy of Being in the Scotist Tradition”).

Identity and Distinction

During the Latin Middle Ages, much speculation was devoted to identity (or sameness) and distinction, in large part because of the need to explain that God is Triune. Theologians needed to uphold, on the one hand, that the Divine Persons of the Trinity were distinct persons and not merely modes or masks that the one God would wear, and, on the other hand, that the Three Persons did not make the one God into three distinct Gods. In general, St. Bonaventure sets the terms of the debate when he names three types of distinction:

There are only three modes of differing, namely, according to modes of being or emanating, as one [divine] person differs from another; according to modes of relating, as a [divine] person differs from the [divine] essence—since one person is referred to another, and is thus distinguished, but the essence is not referred to another and therefore not distinguished—also, according to modes of understanding, as one substantial property differs from another, like goodness and wisdom (Breviloquium I, c. 4).

The first sort of distinction comes to be known as a real distinction, the second as an attributional distinction, and the third as a distinction of reason. St. Bonaventure argues that a real distinction is the greatest of the three because when things are really distinct, we cannot say that one is predicated of the other. The Divine Word cannot be said to be the Father just as Peter cannot be said to be Paul. The attributional distinction, which St. Bonaventure seems to apply only to God, is a middle distinction because one of the things can be predicated of the other but not vice versa. Thus, we legitimately say that the Divine Word is the divine essence, but we could not say that the divine essence is the Divine Word. We cannot say the latter because a Divine Person is distinguished from the other Persons and related to them, but we cannot say such things of the divine essence. Finally, the distinction of reason is the least distinction, founded upon the fact that such things connote differently. They are truly said of each other and the same things can be said of them, but they have different connotations (Breviloquium I, c. 4). For St. Bonaventure, all the divine attributes, such as wisdom and goodness, are identical in God, but because wisdom connotes something different from goodness to us, we are unable to understand how they can be one (On the Mystery of the Trinity, q. 3, a. 1). Thus, the divine attributes are distinct according to our way of thinking even though they are really one in God (Edwards, “St. Bonaventure on Distinctions”).

This general framework would be found in various authors throughout this period. However, there are four other distinctions to keep in mind: Aquinas’s real distinction between essence and act of existence (actus essendi), Henry of Ghent’s intentional distinction, and Scotus’s formal distinction and modal distinction. The first is a specific type of real distinction, and the others are additional distinctions above and beyond those already mentioned. In many of his writings, St. Thomas distinguishes between a thing’s essence and its act of existing.{2} The most famous argument is in De ente et essentia, c. 4, where he explains how an angel could be distinct from God even though it is immaterial. Whatever is not included in the understanding of an essence is not part of the essence and has to come to that essence from outside. But even a perfect understanding of an essence would not tell us whether that essence exists. To use an example from Edward Feser, if we were given a perfect explanation of the essence of lion, pterodactyl, and unicorn and told that one currently exists, one used to exist but does not anymore, and that one has never existed, we could not determine which is which just from the essence (Feser, Five Proofs of the Existence of God, 118). Thus, a thing’s essence and existence are at least conceptually distinct. Furthermore, there could be at most one thing whose essence and existence are identical. Thus, if there is going to be numerically more than one thing, the others must be really distinct. This is so because there can only be a multitude of things if they are distinct as genus and species, which results in a variety of essences, or because the same species has been received into matter many times, which results in a variety of individuals. And if there is something that is existence alone, then it would not receive either of these differences. If it received a distinction rendering it a genus or species, then it would not be just existence anymore; it would be existence and that distinction. And if it were material, then it would not be subsisting existence but material. Thus, it is impossible for there to be more than one thing which is its existence. Therefore, everything other than that one being will have to have its existence as a distinct principle within it from its essence. And having shown that essence and existence are really distinct, he then shows that the one being exists and is God.

Henry of Ghent argues for the existence of an intentional distinction. An intention is produced by the intellect as “something really pertaining to the simplicity of some essence, which is naturally suited to be conceived precisely without something else from which it does not differ in an absolute thing, which similarly pertains to the same thing” (Quodlibet V, q. 6, 161rL). More simply, an intention is an aspect of a thing that we can consider in its own right, independent of the rest of the thing. Since an intentional distinction is produced by the mind, it seems like a distinction of reason, but Henry insists that an intentional distinction is more than a distinction of reason because “in things diverse according to intention, one concept in its way excludes the other according to its way, but it is not so in a difference by reason alone” (Quodlibet V, q. 12, 171rV). For example, Henry uses two examples: (1) “man” and “rational animal” and (2) “white” and “rational.” The first distinction is between a term to be defined and its definition, and these are distinct by reason alone. The second distinction is an intentional distinction since even though “white” and “rational” exist together in some individual, we can consider each concept independently (Pasquale Porro, “Henry of Ghent,” SEP). Importantly, Henry thinks that essence and existence are distinct according to an intentional distinction. For him, they are a weaker sort of intentional distinction such that existence is a sort of relation (respectus) that comes to the essence (Macken, “Les diverses applications de la distinction intentionelle chez Henri de Gand”).

Scotus argues for a formal distinction which falls between a real distinction and a distinction of reason. For Scotus, a real distinction exists between things in reality (ex natura rei) without any action of the intellect, and it entails the separability of the two things. Since essence and existence are not really distinct in this way, he denies Aquinas’s position. A distinction of reason occurs because of an act of the intellect, and it is compatible with the identity of the things that are distinguished. Thus, Aquinas and Scotus are really distinct, but Aquinas and the author of the Summa theologiae are rationally distinct. A formal distinction is ex natura rei like a real distinction, but it is incompatible with the identity of the thing. A common example is the animality and rationality of Peter. Peter is legitimately both animal and rational, but animality and rationality have different formalities because their definitions are different and the definition of one does not include the definition of the other. Moreover, the two cannot be separated. Thus, they are formally distinct within Peter (Lectura I, d. 2, p. 2, qq. 1–4, n. 275; cf. Wolter, The Philosophical Theology of John Duns Scotus, 27–41; King, “Scotus on Metaphysics,” 22–25).

Scotus also posits a modal distinction, which is a weaker sort of distinction between the formal distinction and a distinction of reason. For Scotus, this distinction accounts for the fact that some things, like whiteness, come in degrees. The intensity of the whiteness is an intrinsic mode of it because it explains how the whiteness exists. One the one hand, we could consider this shade of whiteness just insofar as it is whiteness or we can consider it with precisely the degree or intensity of whiteness that it has. By the first consideration we understand it more generally, and by the second consideration we understand it more particularly and perfectly. But our diverse considerations of the whiteness, with or without its degree of brightness, do not involve a mere distinction of reason. It is a feature of whiteness itself that it comes in these intrinsic modes, and, therefore, the distinction is real insofar as it is found in reality (ex natura rei). However, since the whiteness and its intensity are not distinct as two separable things, Scotus concludes that they are distinct as reality and the proper and intrinsic degree (modus) of the reality (Ordinatio I, d. 8, p. 1, q. 3, nn. 138–140; cf. King, “Scotus on Metaphysics,” 25–26).

Structure of Reality

Transcendentals

Since metaphysics studies being insofar as it is being, it is a primary task of metaphysics to discover what is true of every being just insofar as it is a being. These aspects of reality that are true of every being regardless of the many differences between them are called the transcendentals. They receive this name because they transcend every category. For instance, they apply equally to a dog, its brownness, and the relation offspring-of-this-mother-dog, and so on. Moreover, since they transcend every modality of being, transcendentals apply equally to what is mind-independent and what is mind-dependent.{3} Medieval philosophers generally identify one, true, and good as transcendentals, although there are some others included as well, as we will soon see.

Thomas Aquinas gives his most systematic account of the transcendentals in De veritate, q. 1, a. 1 (Disputed Questions on Truth, 1256). The transcendentals are said to add to being insofar as they express a mode of being that follows upon every being but is not expressed in the name “being.” There are two sorts of transcendentals. The first sort follows upon being in itself and the second follows upon being as ordered to another. The transcendentals that follow upon being in itself either express something affirmatively or negatively. Affirmatively, we find that every being is a “thing” (res) insofar as it has an essence. Negatively, we find that every being is “one” (unum) because it is not divided. The transcendentals that follow upon being as ordered to another are further divided. In one mode, we find that every being is divided one from another, which we express by the name “something” (aliquid). In another mode, we find an agreement of one being to another, which can occur either to a knowing power or to a desiring power. The ordering of a being to a knowing power is expressed by the term “true” (verum) and the ordering of a being to a desiring power is expressed by the term “good” (bonum). Thus, in this text, he argues that every being is thing, one, something, true, and good.{4}

Scotus likewise emphasizes that the transcendentals are most general and do not have a category above them. They are coextensive with being and common to many lower divisions of being. He immediately concludes that being has certain characteristics (passiones) that are convertible with it absolutely, and these he names one, true, and good. He also notes that certain characteristics (when taken in tandem) are also convertible with being (e.g., necessary or possible, act or potency, infinite or finite). Scotus says that these “disjunctive attributes,” as they have come to be called, are transcendentals, he says, because they follow upon being insofar as being is not determined to any one genus. Neither necessary being nor possible being is determined or determinable to any one genus or category. Importantly, he notes that one member of the disjunction belongs only to one being, that is, to God. So, the disjunction “necessary being or possible being” transcends every being whatsoever, including God, but “necessary being” applies only to God because he alone must exist. The same is true of “infinite” in the disjunction “infinite or finite being.” (Ordinatio I, d. 8, p. 1, q. 3, nn. 114–15).

Scotus takes an idea from St. Anselm (1033/4–1109) when he speaks of certain “pure perfections” (See Anselm, Monologion, c. 5). Pure perfections are properties that are better to have than their alternatives and make their possessor better absolutely speaking. They are not transcendentals in the strict sense since they are not coextensive with being, but they are transcendental insofar as they are more perfect than other possible attributes. Scotus seems to argue that pure perfections are the better part of disjunctive transcendentals. Wisdom, for example, is transcendental since it is better to be wise than not, and the transcendental disjunctive would be “wisdom or non-wisdom” (Ordinatio I, d. 8, p. 1, q. 3, n. 115; Quodlibet q. 1, nn. 8–12; Quodlibet q. 5, nn. 20, 23). As Peter King notes, according to Scotus, pure perfections are better to have even if they are contrary to the nature of a thing. A dog cannot be wise without ceasing to be a dog, but it would be better to be wise than to continue being a dog (King, “Scotus on Metaphysics,” 27). So, when Scotus says that they are pure perfections, he takes the word “pure” seriously. They are not perfections relative to the thing but rather perfections absolutely speaking.

Categories of Being

Since it is obvious that not all properties and terms are transcendental, a certain division of being is necessary. Unlike the transcendentals, which St. Thomas calls “general modes of being,” the categories are “special modes of being” because they name a special way of being. They cannot designate species of being since being cannot be a genus. A species’ specific difference has to be taken from beyond the genus and added to it. But nothing is beyond being, so the categories of being name special modes of being not expressed by the very name “being” (De veritate, q. 1, a. 1). Following Aristotle’s claim in Categories, c. 4 and Topics I, c. 9, Aquinas claims that there are ten categories: substance, quantity, quality, relation, time, place, posture, habitus (that is, being equipped), action, and passion (that is, being acted upon). Aristotle does not offer much explicit argumentation for the reason behind this exact list of categories. However, Aquinas offers a derivation from being into the ten categories in his Commentary on Aristotle’sMetaphysics. A predicate can refer to a subject either (1) as signifiying what the subject is, (2) as being in the subject, or (3) as being taken from something outside the subject. From the first sort of predication, we get the category of substance. The second sort of predication is further distinguished into when the predicate is (2a) in the subject essentially and absolutely from the matter, from which we get the category of quantity, or from the form, from which we get the category of quality, or (2b) in the subject relative to something else, from which we derive the category of relation. The third sort of predication is also subject to several sets of distinctions. The first distinction is into (3a) predicates that are completely outside the subject or (3b) those partially outside and partially inside the subject. These predicates completely outside the subject might not be a measure of the subject, from which we derive the category of habit, or they might be a measure of the subject. In this case, they might measure the thing temporally, which is the category of time, or they might measure the subject with regard to place. The measure with respect to place might not consider the distribution of the parts, which is the category of place, or it might consider the distribution of the parts, which is the category of position. Those predicates that are (3b) partially within and partially without the subject, can be such as a principle, which is the category of action, or partially without, which is the category of passion (Commentary on Aristotle’s Metaphysics, bk V, lect. 9, n. 891–92; Wippel, Metaphysical Thought of Thomas Aquinas, 208–28).

Henry of Ghent objects to this derivation of the categories. In a reply to an objection in Summa, he argues that things can be distinct from each other in many ways (a. 27, a. 1 [fol. 161vM]). The relevant sort of distinction for our purposes would be when things differ in reality. This is either absolute on the part of both things or relative at least on the part of one of them. The absolute or non-relative things are the categories of substance, quantity, and quality. When things are really distinct because of a relation, that relation between them is either founded in the nature and the essence of the thing or the relation is founded upon an accident in the thing. When the relation is founded upon an accident, it can be separated (i.e., when the likeness between Socrates and Plato, which is founded on their respective heights, is lost when one grows taller or shrinks). As Roland Teske notes, separability seems to be the criterion for the real distinction between them (“Distinctions in the Metaphysics of Henry of Ghent,” 231). When the relation is founded upon the nature and essence of the thing, it is inseparable. Thus, Henry has reduced the categories of being to four: substance, quantity, quality, and relation. The other six categories that Aristotle had identified would, according to Henry, be merely species of relation.

John Duns Scotus takes issue with both these accounts for different reasons. Aquinas’s account is erroneous both because it fails to show that there are ten fundamental categories of being and because it begs the question. It fails to show that there are ten categories because it does not immediately divide being into the ten categories. Instead, it divides it into three categories which are then subdivided into the ten. Most other divisions first divide being into “being per se” and “being not per se” and then subdivide the latter division into the other nine categories. Thus, their arguments show that being is divided into two or three fundamental categories, not ten (Questions on Aristotle’s Metaphysics V, qq. 5–6, n. 73–74). Moreover, their arguments beg the question because “it would be necessary to prove that what is divided is thus divided, and precisely in this way, and this is the proposition in question, namely, that the dividends constitute the most general categories” (Questions on Aristotle’s Metaphysics V, qq. 5–6, n. 75; See Gracia and Newton, “Medieval Theories of the Categories,” SEP, sect. 5.1).

Despite his dissatisfaction with his predecessors’ arguments, Scotus agrees with their conclusion that there are ten categories and insists that this distinction is not merely logical but metaphysical as well (Questions on Aristotle’s Categories, q. 11, n. 26). The only conclusive proof, however, that there are ten and only ten categories is to go through each category individually and examine its essence.{5}

This debate is important to note because the nominalist tradition will continues the trend of reducing the number of categories. For example, William of Ockham argues that there are only two categories: substance and quality (Summa logicae I, c. 41; Quodlibet V, q. 22). At the risk of oversimplifying, he generally agrees with the arguments that divide being into “being in itself” and “being in another,” and with Scotus’s critique that these arguments reduce the number of categories to two. He is willing to entertain ten categories as logically distinct since they are answers to questions such as “what is it?” “how much? “what kind?” and so on, but only substances and their qualities exist in reality. In the case of quantity, he argues that it is simply part of substance. His argument is based on his account of divine omnipotence. If substance and quantity were distinct in reality, then God could make a substance without its quantity. To have quantity is to have parts outside of parts. Thus, if substance and quantity were distinct, then God could make a substance like wood without any quantity. But that wood would still have parts outside of parts in virtue of being a substance. Therefore, quantity is not a distinct reality from substance (Summa logicae I, c. 44). Thus, all that exists for Ockham are substances and their qualities.

Causality

Following Aristotle, every author in this time period argues that there are four essential causes: material causality, formal causality, efficient causality, and final causality. The material cause of a thing is that out of which it is made which persists in the finished product. Thus, the material cause of a knife would be the metal of the blade and the wood of the handle. Its formal cause is the form or nature which makes the thing to be the sort of thing that it is. Thus, the formal cause of a knife is the form of knife which entails the characteristic shape, weight distribution, sharpness, etc. The efficient cause of a thing is the initiator of the motion or rest which makes the thing. The efficient cause of the knife is the knife-maker. A thing’s final cause is the end or goal toward which it strives and in which it finds its perfection. Thus, the final cause of the knife is to cut. Since none of these causes overlaps with or could replace another, authors argue that complete and scientific knowledge of something is achieved only when all four causes are known of it. As a result, these four causes are investigated everywhere. We even find authors analyzing the existence of Peter Lombard’s Book of the Sentences and books of the Bible in terms of the four causes (See, e.g., Bonaventure, In I Sent., proemium, qq. 1–4 and Commentary on Ecclesiasties, proemium, n. 16).

A few details need to be added to this very general initial account. First, formal causality can be either intrinsic or extrinsic. Intrinsic formal causality refers to the form of knife in the knife itself. The knife itself has this particular shape, sharpness, and so on. The form of that knife does not just exist in the knife, however. It also exists in the mind of the knife-maker who thought out the knife before making it. The intrinsic form in the knife itself and the extrinsic form in the mind of the knife-maker have to be the same in species since the extrinsic form is the pattern in imitation of which the intrinsic form comes to be. However, the extrinsic form existing in the mind does not act in the same way as the intrinsic form. The intrinsic form is a principle of being, making the metal to be a knife; the extrinsic form is a principle of knowing, making the knife-maker to know knife. Authors apply this extrinsic formal causality to all instances of causality by art, including God’s creating the world according to the pattern of the divine ideas (See Vater, God’s Knowledge of the World). However, there is an important disanalogy between the knife-maker and God which should be noted. Even though both are producing by art, God produces something natural, and the artist produces something merely artificial. When the form of knife is educed from the metal, the metal remains metal even as it is shaped into a knife. Thus, the form of knife does not penetrate to the heart of the being. When God makes, however, He makes the whole thing such that a dog is dog all the way to its core. So, while it is acceptable to speak of the form of knife as intrinsic to the knife, it is not intrinsic in precisely the same way as the form of dog in Fido.

Second, efficient causality is never just one agent producing one effect. The total efficient cause is always complicated in two different ways. In one way, many agents frequently cooperate as partial causes of the effect, as when many people pull a boat up the shore beyond high tide. None of them is sufficient to pull the boat and each of them is a partial cause of the motion and new location of the boat. In another way, many agents cooperate in a hierarchy such that each is the total cause of the effect. Sometimes these agents are related as principal cause and instrumental cause. In these cases, the principal and instrumental causes each produce the whole effect, but the effect is beyond the capacity of the instrumental cause by itself. For example, when someone writes a sentence on a chalkboard, both the writer and the chalk are causes of the whole effect, but language is totally beyond the capacity of chalk in itself. In theology, certain schools (including the majority of those following St. Thomas) would apply this sort of causal relationship to a variety of revealed realities: scriptural inspiration, Christ’s sacred humanity, sacramental causality, and the working of miracles (Hugon, God's Use of Instrumental Causality). At other times, these agents are related as primary and secondary causes. This relationship is like the relationship of principal and instrumental causes, except in these cases the secondary cause is capable of producing the effect itself. A violinist can cause violin music all by himself, and yet he operates as a secondary cause of the conductor who is directing the entire orchestra. The conductor gives to the entire orchestra and to each of the musicians their acts of playing (Dodds, The Philosophy of Nature, 48–49). Authors describe every act of creatures using the model of primary and secondary causes because God is the primary cause of every act, and the creature is the secondary cause.

Third, although final causality is easiest to understand with an example of a knower like the knife-maker, authors insist that every being whatsoever acts for an end. The ends of things are built into their natures. Thus, when a hydrogen atom seeks another hydrogen atom and exists as a diatomic molecule, it is acting for the end of self-preservation. The thing acting for an end might not be cognitive, but the one who established its nature was intelligent and gave it the natural tendency to act for its end.

Hylomorphism and Individuation

Form and Matter

There is unanimous agreement among the philosophers of the medieval period that physical beings are composed of two intrinsic principles: form and matter. Form is the determining causal principle of a thing, and matter is its “determined” principle. These two principles are necessary in order to account for the reality of change as opposed to creation and annihilation. In change, there is a continuity from the beginning of the change to the end of the change. But if things are not composed of two principles, one which remains constant while the other one changes, then what we call change would really be the destruction of one being and the creation of an entirely different being. Thus, the reality of change actually requires three distinct principles: form, matter, and privation. Form is the new actuality that the changing being acquires at the end of the change. Matter is the principle of stability that underlies the change and is present at the beginning and end of the change. Privation is not a principle in itself but refers to the initial lack of the form that is acquired in the change. For example, when a sheet of metal is changed into a knife, the privation is the lack of form of knife. By virtue of being shaped into a sheet, the metal lacks the form of knife. The form is knife, which is acquired at the end, and the matter is the metal itself. When someone learns the Pythagorean Theorem, there is an initial privation of that knowledge. The form is the knowledge of the theorem, and the matter is the knower.

This general account is expanded when we consider that there are two types of change: accidental change and substantial change. Accidental change occurs when the being or substance at the beginning of the change is the same as the being or substance at the end of the change. The metal at the beginning is substantially the same as a sheet and as a knife. I am substantially the same when I pass from ignorance of the Pythagorean Theorem to knowledge of it. In these cases, the matter is the substance itself and the form is some accidental form in one of the other nine categories. Substantial change occurs when the substance itself is what changes such that the substance at the beginning of the change and the one at the end of the change are distinct substances. This occurs in conception and death, the digestion and assimilation of food, and the generation or corruption of chemical compounds from elements. When I eat an apple and assimilate the nutrients in it, I don’t slowly become apple. Instead, the apple is changed into me and becomes human. In these cases, the substance cannot be the matter since it is what is changing. As a result, we discover a formal and material principle within substance itself, which we call substantial form and prime matter. Substantial form is the principle that makes the thing to be the sort of thing that it is, and primary matter is the thoroughly non-formal principle of potency which makes the change possible (see, among others, Aquinas, On the Principles of Nature, cc. 1–2).

Prime matter is a source of great intellectual difficulty because its nature is thoroughly foreign to us. The view of Aquinas is that prime matter lacks all actuality. It is pure potency. But since things only exist insofar as they are actual, not even God could make prime matter exist without form (Aquinas, Quodlibet III, q. 1, a. 1). Aquinas’s view was common insofar as he says that matter never exists without being actualized by some form.{6} Yet, there were many who thought that prime matter had some sort of actuality and thus could be made by God apart from every form (John Pecham, Quaestiones disputate, fol. 37vB; Richard of Mediavilla, In II Sent., d. 12, a. 1, q. 4; Scotus, Reportatio Parisensis II, d. 122, q. 2, n. 4 and following; Sharp, Franciscan Philosophy at Oxford in the Thirteenth Century).

Among medieval philosophers, there was also a twofold controversy about the number of substantial forms in a being and the scope of form-matter composition. Although they differed in many details, most authors argued that there are many substantial forms in one being such that it would have one form by which it is bodily, another by which it is living, another by which it is an animal, and another by which it is rational and human.{7} This position has its origin in the view of the Muslim philosopher Avicebron (Ibn Gabriol) in his work Fons vitae. One argument is based on the likeness of the body and the corpse it becomes upon death. If there were no other substantial forms, then there is no reason to think that the new substantial form will result in a corpse that looks anything like the body. They also point to the Church’s practice of venerating the bones of the saints and the belief in Christ’s body in the tomb, which do not make sense if the “bones” are not in any way the same substance as the saint or Christ (see, especially, Ockham, Quodlibet II, q. 11).

Aquinas is in the minority in his objection to the plurality of substantial forms. According to him, there are two difficulties with positing many substantial forms. First, if there are many substantial forms, how can we account for the unity of the substance? Second, a substantial form, he argues, gives substantial determination as opposed to determining the being in a qualified way as an accidental form does. This substantial determination is distinguished from qualified determination by being the first act and determination of the being. Fido is first a dog and then is changed in a qualified way by this height or that weight. Both changes make Fido to be in a certain way, but they do not make him be at the most fundamental level. But if there are many substantial forms, then only one of them will be first and give substantial determination. All the other supposed substantial forms would only change the being in a qualified way, which would make them accidental forms. Thus, if there are many substantial forms in Fido, he will be substantially a body and only accidentally a dog (Disputed Questions on Spiritual Creatures, a. 3).

There was also a question about the scope of matter-form composition. The majority position was called universal hylomorphism, which held that all finite beings, regardless of whether those beings were material (like dogs and cats) or immaterial (like angels), are composed of form and matter, which the philosophers call “intelligences” or “separate substances.” Matter is further distinguished into corporeal matter and spiritual matter. Corporeal matter is subject to the three dimensions of bodily things, and spiritual matter is simply a principle of potency. “Matter” is the name of the only principle of potency; so if any finite being lacked matter, then it would lack potency and be pure act. However, the only being that is pure act is God, which would mean that a finite being would be equal to God, which is contradictory. (See, e.g., Bonaventure, In II Sent., d. 3, q. 1, a. 1; Richard of Mediavilla, In II Sent., d. 3, a. 1, q. 2)

Aquinas objects to the notion of universal hylomorphism for two reasons. First, he argues that it is contradictory to say that matter is distinguished into corporeal and spiritual matter. In order for matter to be thus distinguished, it would have to have parts, one corporeal and one spiritual.. But whatever has parts has quantity, and whatever has quantity is corporeal. Thus, the supposed spiritual and immaterial matter would in fact be just as corporeal as the rest of matter. Second, he says that his theory of the real distinction of essence and existence can solve the problem. Even though angels would not have matter as a principle of potency, they would still have their own essences as principles of potency. They would not be pure act like God. As a result of this second argument, Aquinas says that the dispute over universal hylomorphism is more a dispute over language than substance (On Separate Substances; Summa theologiae I, q. 50, a. 2). One of the consequences of Aquinas’s position is that there cannot be more than one angel per species since there is no matter by which they would be distinguished as individuals. Thus, every angel is its own species, and angels are arranged in a strict hierarchy of essences (Summa theologiae I, q. 50, a. 4). It is worth noting that Aquinas’s position seems to have been condemned by Bishop Tempier in 1277, as evidenced by the fact that the bishop condemned the following propositions: “Since intelligences do not have matter, God could not make many of the same species” (n. 81), and “That God cannot make many individuals under one species without matter” (n. 96). It is a matter of dispute whether these condemnations are meant to include Aquinas or not. What is known for certain is that on February 14, 1325, a year and a half after St. Thomas was canonized on July 18, 1323, the Bishop of Paris, Stephen Bourret, revoked the condemnations of 1277 insofar as they seem to touch on the teachings of Saint Thomas (Chartularium Universitatis Parisiensis II, n. 838).

Three Theories of Individuation

The distinction of form and matter raises yet another difficulty: the question of individuation. There are many ways of interpreting this question, but the one that concerns us most here is how individuals come to be. The form of dog makes Fido to be a dog, but the form of dog also makes Spike to be a dog too. So, how do we account for the fact that Fido and Spike are two distinct dogs? St. Thomas’s answer is to say that matter designated by quantity (materia signata quantitate), or signate matter, is the principle of individuation. Signate matter is matter that has been rendered divisible by quantity such that the form of Fido can be received into this portion of matter here and now and the form of Spike can be received into that portion of matter here and now. He emphasizes that the sort of portions or dimensions of matter that make for the principle of individuation are not any determinate measure or shape. If they were, then Fido would have to be such and such a size at all times and would not be able to grow or shrink in any way. Instead, the sort of dimensions he means are dimensions that do not set an exact determination. Just as the nature of color does not set an exact determination of white or black, so these dimensions do not set an exact size (Commentary on Boethius’s De Trinitate, q. 4, a. 2; Wippel, The Metaphysical Thought of Thomas Aquinas, 351–75).

Henry of Ghent’s theory of individuation in some ways agrees with Aquinas’s theory and disagrees in other ways. On the one hand, he argues that matter and quantitative dimensions are the principles of individuation, and he even, like St. Thomas, distinguishes between determinate and indeterminate dimensions (Quodlibet V, q. 8, fol. 165rL–vL). On the other hand, he also declares that matter and quantity are not the “precise reason” (ratio praecisa) and cause of individuation (Quodlibet II, q. 8). From this, he offers two accounts of individuation which are ostensibly meant to work together, although it is unclear how they do so. The first account declares that subsistence is the principle of individuation, although he is not entirely clear about what that term means (Quodlibet II, q. 8; Brown, “Henry of Ghent” in Individuation in Scholasticism). The second account declares that individuation occurs by a double negation (duplex negatio). It is an internal negation insofar as it removes any possibility of plurification and diversity, and it is an external negation insofar as it removes any identity with another individual. Thus, the form in question can be called “this form.” As “this form,” it is neither a form of a different species nor is it a form of another being of the same species (Quodlibet V, q. 8; Summa, a. 39, q. 3, ad 2; Pickavé, “Henry of Ghent on Individuation, Essence, and Being,” esp., 182–89).

John Duns Scotus is dissatisfied with both solutions to individuation. For him, an individual is something that is essentially one among other beings and which cannot be divided into lower parts like a genus. Put another way, individuality is primarily about something being unique and unrepeatable. It is immediately obvious that Henry’s double negation is insufficient because it does not identify the precise character of the individual’s individuality. The metaphysical principle of individuation must be a positive principle, not a negation. According to him, Aquinas’s account fails because it does not take into account the primacy of substance. Substance is an essential being (ens per se), but the aggregate of substance and an accident (like quantitative dimensions) is an accidental being (ens per accidens). So, a substance is not such an aggregate and does not include such an accident (Questions on Metaphysics VII, q. 13, n. 21).

Given these critiques, Scotus’s principle of individuation has to be (1) unrepeatable and (to use a technical term) non-instantiable, (2) substantial and not accidental, and (3) a positive and active principle. Taking these criteria into account, Scotus argues that the principle of individuation is an individual form which occupies the lowest grade of form and is a “thisness” (haecceitas). He argues that just as unity in general follows essentially upon being in general, so every sort of unity essentially follows upon some being. Thus, given that the unity of an individual in its uniqueness exists, there must also be a being or entity providing the metaphysical basis for that individual unity. That positive entity could not be some universal or specific nature because the unity of an individual and the unity of a species are distinct and contrary to each other precisely as regards the question of uniqueness. Therefore, there must be an individual positive entity that renders this being to be individual (Ordinatio II, d. 3, p. 1, qq. 5–6, n. 169). Since this entity is positive and active, he calls it a unique sort of form, but its uniqueness makes it hard for us to explain its nature precisely. He resorts to an analogy to the specific difference dividing a species from a genus. The individual form or haecceity is a form that divides an individual from all others in the species (Noone, “Universals and Individuation,” Dumont, “The Question on Individuation in Scotus’s « Quaestiones super Metaphysicam »”).

Philosophical Theology

For all their differences about the nature of metaphysics, every philosopher in this period thinks that it belongs to metaphysics to discuss the existence and nature of God. St. Bonaventure thinks that it does because metaphysics is primarily about exemplarity, and the exemplars par excellence are found in God. St. Thomas thinks it belongs because it pertains to the science of being qua being to consider the principle and source of its subject. Scotus thinks it belongs because being’s fundamental division is into infinite and finite, so it belongs to the science of being to investigate infinite being just as much as it does to investigate finite being. They offer a host of arguments for God’s existence and seek to understand his essence as much as they can from the results of those arguments. This overview article will not be the place for a detailed discussion of the many arguments offered, but we will consider some of them.

Proofs for the Existence of God

There are many types of arguments offered for God’s existence during this time period, of which we will examine four: (1) from illumination (or from exemplar causality), (2) from causality (often called cosmological arguments), (3) from the very nature of God (derisively named “ontological arguments” by Kant), and (4) from possibility and necessity (or modal arguments). St. Bonaventure offers arguments for the first three, St. Thomas’s arguments are primarily confined to the second type (although his Fourth Way seems to be based on exemplar causality, and therefore belongs to the first type), and Scotus’s argument borrows from the second type for the sake of proceeding to the fourth type.

St. Bonaventure’s illumination argument is based on the fact that we can have certain knowledge of the truth. For Bonaventure, certainty is impossible for any finite being to attain because it requires “immutability on the part of the knowable object and infallibility on the part of the knower” (Disputed questions on the knowledge of Christ, q. 4). But created truth is not absolutely immutable since it never had to exist and is subject to change, and finite knowers are not entirely infallible since they are produced from non-existence into existence. So, it is not just that our knowledge of the truth requires a superior light to illuminate us, but that our knowledge also requires the light of the eternal art which establishes the existence and truth of things for its certainty. He argues that “every right understanding proves God’s existence because cognition of it is impressed upon every soul and every cognition is through it. Every affirmative proposition proves and concludes it, for every such thing posits something; and with something posited the true is posited, and with something true posited the truth is posited, which truth is the cause of every true thing” (In I Sent., d. 8, p. 1, a. 1, q. 2). It is precisely the aspect of certainty of the truth that requires God’s existence. This argument is criticized by a variety of thinkers who disagree with Bonaventure about divine illumination, but Bonaventure is convinced it is a demonstration. Moreover, according to him, it is especially strong because it is based on the exemplar causality exercised by God’s ideas upon human understanding. (Recall that exemplarity is the central feature of metaphysics for him).

Arguments from causality typically begin with some fact of reality and then argue that the only explanation for this fact is the existence of God. The precise details of the argument will depend upon the aspect of reality being considered. St. Bonaventure identifies ten distinct aspects of reality that call for God’s existence: The fact that beings are posterior, from another, possible, relative, diminished/qualified, because of another, by participation, in potency, composed, and mutable cries out for the existence of a being who is prior, not from another, necessary, absolute, undiminished, because of itself, by essence, in act, simple, and immutable (respectively) (Disputed questions on the mystery of the Trinity, q. 1, a. 1, arg. in favor, 11–20). The second of Aquinas’s famous “five ways,” which he says is based on efficient causality, is an especially good example of this sort of argument. We find in sensible things an order of efficient causes. But nothing can be the efficient cause of itself, for then it would exist as causing itself and yet not exist as being caused to exist at the same time. But this order of efficient causes cannot extend unto infinity because each of the causes is currently producing both the existence of its effect and its effect’s ability to cause the following effect. The sort of causality at work is not a linear, historical, family tree sort of series, but a hierarchical series operating here and now (for more on this distinction, see Feser, Five Proofs of the Existence of God, 20–22, 60–66). Therefore, there has to be a first efficient cause, which everyone calls God (Summa theologiae I, q. 2, a. 3).

Interest in the so-called “ontological argument” during this time period comes from St. Anselm’s Proslogion, cc. 2–3, in which he argues that God, whom he calls “that than which nothing greater can be conceived,” not only has to exist in reality, but cannot even be thought not to exist. He derives these conclusions from reflection on the very nature of “that than which nothing greater can be conceived.” Bonaventure’s versions of this argument all connect God to existence by means of two middle terms, one which draws an inference to existence and one which connects that inference to God. For example, Bonaventure argues that God is divine being, that divine being is completely pure being, and that the most pure being must exist (Journey of the Mind to God, c. 5, n. 3). Completely pure being must exist because being is only complete in the full flight from non-being, which means that the completely pure being has nothing of non-being whatsoever. But potency is a sort of non-being because when we are in potency to do something, we are not actually doing it. Thus,it does not exist completely. Completely pure being must be pure being-in-act alone, that is, actual existence. He then connects completely pure being with the divine being by noting that our very conception of non-being (including being-in-potency) only occurs because of being. We only know a lack or privation of being by knowing being. It is only through the pure actuality of being that we can know these things at all. But pure actuality of being must be the divine being since the pure actuality of being is unlimited. Thus, God exists (Houser, “Bonaventure’s Three-fold Way to God”).

Scotus’s modal argument for God’s existence begins much like causal arguments. He offers arguments beginning from facts about the world and progressing to the existence of a first efficient cause, a first final cause, and a preeminent (or maximally excellent) being. He then argues that all three are coextensive, that is, belong to a single being. At this point in the argument, he knows that God exists given that this world exists. But since this world did not have to exist, his argument does not show that God must exist; it only shows that he can exist given the existence of this world. But the very conditions of the possibility of God’s existing make it so that “can” entails “must.” Since God is the first efficient cause, there is nothing that could, even in principle, cause him to exist. Thus, if God can exist, it is only because he already does and must exist (Lectura I, d. 2, q. 1, nn. 38–135; Ordinatio I, d. 2, q. 1, nn. 39–190; Reportatio parisiensis I, d. 2, q. 1; De primo principio).

Divine Attributes

Reflection upon the divine attributes was critical for the medieval philosophers because they recognized that merely showing the existence of some sort of eminent being is not the same as showing that this being is God. Many of the arguments for God’s existence conclude that a being which is pure act exists, but it is not obvious that pure act is God. Thus, authors in this period draw out the implications of pure act to show that this being has all the divine attributes. Although there is not uniformity among various writers concerning the divine attributes, the order in which they should be derived, or the arguments used to derive them, there is nonetheless more agreement here than in many places such that one brief derivation will suffice for our purposes (See Feser, Five Proofs of the Existence of God, ch. 5).

First, there can only be one being that is pure act. If there were two gods, they would have to be distinct as individuals of the same species or two species of the same genus. But both options require the composition of metaphysical parts such that one part is in potency to being actualized by the other, just as animality is in potency to be actualized as reptile or fish. Thus, the existence of two gods is incompatible with pure act.

The one being which is pure act must also be simple (that is, not composed) because all composition entails potency since the parts can be united. Moreover, composite beings require another being to compose them, which means that all composite beings are in potency to being united. Therefore, pure act is simple. (For an account of the types of arguments for divine simplicity, see Vater, “Medieval Accounts of Divine Simplicity”). This unanimous agreement about God’s simplicity is important to note since many contemporary authors deny it (e.g., Alvin Plantinga, Does God have a Nature?; J.P. Moreland and William Lane Craig, Philosophical Foundations for a Christian Worldview, 517–36). Their arguments are in part based on the fact that divine attributes like wisdom and goodness do not seem to be identical, and so they seem to be distinct properties of God. But if they are properties, then God has some sort of composition (See Dolezal, God without Parts for a book-length reply to these objections).

The one, simple, purely actual being must be immutable. Change is the actualization of a potency, which means that only beings in potency can change. But the purely actual being lacks all potency and so cannot change. From these first four attributes immediately follow immateriality and incorporeality. Matter is, as we have seen, a principle of potency and entails having both sensible and metaphysical parts. But the purely actual and simple being could not have potency or parts. So, it is also immaterial and incorporeal. It also follows that this being is eternal. Pure act can neither come into being nor pass out of being, but whatever is such is eternal. Moreover, his eternity is strictly timeless and not mere longevity. The passage of time entails change from one moment to the next, but this being is immutable. Thus, it is eternal and timeless. This being is also necessary because whatever cannot not be is necessary. But pure act is and cannot fail to be. Thus, this being is necessary. Since pure act is the source of all other acts, both the acts that are and the acts that could be, it is also omnipotent.

God is also omniscient and pure love. Since anything that does or could exist depends on God’s causal action at every moment and since every effect exists in its cause in some way, God must have every creature within him. Creatures cannot exist in God naturally. This is because a creature would then be unlimited and eternal like God, which is contrary to the very nature of a finite being, and also because some part of God would then be limited, which is contrary to his nature as pure act. Thus, creatures must exist in God in another manner: an intellectual manner. He does not know creatures by learning about them, since that implies the potency of coming-to-know. Instead, he knows them as a consequence of knowing his own essence. Authors disagree sharply about how he knows them because of knowing his own essence, but they agree that the only source of God’s knowledge is his own essence and that he knows creatures by knowing his own essence (for more on these arguments, see Vater, God’s Knowledge of the World). God is also pure love because to love is to will the good of the beloved. God wills both his own good and the good of everything that he creates. Thus, he loves and has perfect love in bestowing existence on creatures who in no way earned or deserved to exist. This being is also incomprehensible because nothing infinite can be comprehended by a finite mind.

This being is thus pure act, one/unique, simple, immutable, immaterial and incorporeal, eternal, necessary, omnipotent, omniscient, all-loving, and incomprehensible. But when we use the word “God,” we mean precisely such a being. Therefore, the being proved to exist in the arguments above is God.

IV. Human Nature

Philosophers during this period saw their view of human nature as an outgrowth of their view of nature in general. Since, as we have seen, nature is a hylomorphic composition of form and matter, it follows that we too are composed of form and matter. We call our form “soul” and our matter “body.” Philosophers in this period were highly influenced by the sections on the soul found in Avicenna’s work The Healing (or The Cure) as an authoritative articulation and deepening of Aristotle’s work, though they do not follow him on everything, and by Averroes’s Long Commentary on Aristotle’s De anima.

The human soul poses a special difficulty for our authors because they all believe that it is incorruptible and will survive the death of the body. The difficulty is that it seems to be a form actualizing the body in one way, but it also seems to be something in its own right (to use the technical term, hoc aliquid) since it can exist without the body. Some authors like Alexander of Hales, Jean de la Rochelle and St. Bonaventure argue that the soul is both a form and a hoc aliquid (Alexander of Hales, Summa theologica II, p. 2, inq. 4, tract. 1, sect. 1, q. 1, c. 2, n. 321; Jean de la Rochelle, Summa de anima I, cc. 8 and 22; Bonaventure, Breviloquium, p. 2, c. 9).

Aquinas objects to this double-identification of form and hoc aliquid, saying that it is contradictory. Properly speaking, a hoc aliquidis an individual in the genus of substance. So, Fido is a hoc aliquid. But an individual in the genus of substance has two characteristics: (1) it is subsistent and (2) it is something complete in a particular genus and species of substance. The human soul has the first characteristic but not the second, since the species man is not soul alone but also body. Thus, the soul is not, strictly speaking, in a genus or species except “by reduction.” The human soul is in the species man by reduction because it is the formal principle by which an individual man exists. So, the human soul is a form, but it is also subsistent because it has an activity that does not depend upon the body (Disputed Questions on the Soul, a. 1; B. Carlos Bazán, “The Human Soul: Form and Substance? Thomas Aquinas’ Critique of Eclectic Aristotelianism”).

Human nature exhibits many powers. If an author thinks that there is but one substantial form (i.e., one soul) in us, then all these powers will flow from that one soul. If an author thinks that there are many substantial forms, then each power will flow from the appropriate soul-stratum. The first powers of a living being are the vegetative functions of nutrition, growth, and reproduction. The second set of powers are sense powers, which are distinguished into those associated with apprehension and cognition and those associated with desire. The apprehensive or cognitive powers are the five external senses (sight, hearing, smell, taste, and touch), and the internal sense powers (common sense, imagination, cogitative power, and memory). Common sense receives all the cognition of the external senses, provides awareness of occurrent sensation, and distinguishes the proper objects of each external sense power (e.g., the distinction between white and sweet). Imagination builds up what it receives from the common sense so as to form, as it were, an image of the object in general and preserves it so that we can sense the object even when it is absent. The cogitative power (also called estimative power) receives certain intentions (the term coming from Avicenna) that are not directly sensed by any of the external sense powers. The cogitative power is responsible for knowing the individual as an individual (e.g., Socrates), an individual of a certain type (e.g., this man), judging what the individual is capable of (e.g., this water is potable), and making a judgment about (for the purpose of interpretation) the thing relative to the knower such that we know the thing to be suitable for us, harmful for us, or indifferent to us (Deely, What Distinguishes Human Understanding?, esp. ch. 4; De Haan, “Perception and the Vis Cogitativa: A Thomistic Analysis of Aspectual, Actional, and Affectional Percepts”; Jalsevic, “Mitigating the Magic: The Role of the Memory, the Vis Cogitativa, and Experience in Aquinas’s Abstractionist Epistemology”). Those intentions are then preserved in the memory together with an explicit cognition of past sensations as past.

The judgments “suitable”, “harmful,” or “indifferent” made by the cogitative power immediately result in the sense desires which authors call passions or emotions because we are immediately inclined toward acquiring what we judge suitable and away from what we judge harmful. The most developed theory of passions from this period is that of St. Thomas. He identifies eleven general passions. First, passions are distinguished into concupiscible and irascible. Concupiscible passions concern an object insofar as we judge it good for us or bad for us, and irascible passions concern an object insofar as we also consider that the object will be arduous to attain (if good) or to avoid (if bad). The concupiscible passions are distinguished according to whether the object is good or bad for us and whether we have an inclination to the object, a motion in response to it, or are resting in the possession or presence of it. The passions toward a good object are love, desire, and delight/joy, and the passions toward a bad object are hate, flight, and pain/sorrow. If an object will be difficult for us to attain, two irascible emotions spring up with regard to our motion in response to it. If the object is an arduous good, then we will have hope of obtaining it (because the object is good) and despair of obtaining it (because of the difficulty). If the object is an arduous bad, we will experience the passions of fear insofar as it is bad and daringinsofar as we are moved to overcome the difficulty. Finally, when we experience pain or sorrow at a present evil, we might also experience the irascible passion of anger which seeks vengeance for an injustice done to us (Summa theologiae I-II, qq. 22–49; Lombardo, The Logic of Desire).

Since we recognize within ourselves the ability to know things not merely in their relation to ourselves but also in themselves and independent of any particular instantiation, we are led to posit additional powers above and beyond the senses. These intellectual powers are also distinguished into an apprehensive power (which is called intellect) and an appetitive power (which is called will). Intellect acquires a universal knowledge of the essences of things from the content of the phantasm in the internal sense powers, especially, it seems, in the cogitative power.{8} However, this knowledge cannot be given directly by the internal sense powers because they preserve certain individualizing aspects of the thing known. Thus, following Aristotle, the medieval philosophers argue that there are two intellects: a possible intellect which receives all intellectual knowledge and an agent intellect which is responsible for abstracting the intelligible content of the phantasm for the possible intellect. The precise nature of these two intellects varies widely. St. Bonaventure identifies eight possible views of the possible and agent intellect which both capture the historical views of several authors in our time period and foreshadow the views of later authors. This eightfold division is not entirely exhaustive, but it is close to being so.

The first two ways of understanding the possible and agent intellects are as two substances. According to the first way, the agent intellect is not part of the human person but is instead a separate substance with which the possible intellect conjoins when it comes to know. Thus, all our knowledge flows from the illumination of this angel-like being. This view was held by Avicenna (De anima V, c. 5). Bonaventure does not mention it here, but there is also the view of Averroes, who holds that both the agent and possible intellects are separate substances. Most authors reject this view on the ground that, if our intellect were not part of our soul, we could not legitimately claim to think as individuals (see Bonaventure, In II Sent., d. 18, a. 2, q. 1; Aquinas, De unitate intellectus) According to the second way, the agent intellect is God himself, and the possible intellect is our mind. On this view, all our intellectual knowledge would be given by God with us having no part in it. This view was held by William of Auvergne (De anima, c. 7, p. 5).

The third and fourth ways of understanding the agent and possible intellect are as two powers. The third way posits that the possible intellect is purely passive (or, as Bonaventure puts it, material) and the agent intellect is purely active (or, as he puts it, formal). This view seems to be grounded on Aristotle’s claim that “the possible intellect is that by which it becomes all things; the agent intellect that by which it makes all things” (De anima III, c. 5, 430a12–15). This view is found in the Summa theologica ascribed to Alexander of Hales, St. Albert the Great (De homine, q. 55, a. 5, par. 1), and Aquinas (Summa theologiae I, q. 79, aa. 1–4). The fourth way agrees with the third in appropriating potency to the possible intellect and act to the agent intellect, but it denies that either is purely such. The possible intellect is also active insofar as it must turn itself to the species existing in the phantasm, and the agent intellect is in potency insofar as awaits the species in the imagination and is aided by it.

The fifth and six views of the two intellects declare that they differ as a power and a habit. The fifth understanding says that the agent intellect is a habit constituted from all intelligible objects, and that the possible intellect is a power capable of acquiring all those objects. The agent intellect is said to require this innate knowledge because otherwise it would have no access. This view was held by Jean de la Rochelle (Tractatus de divisione multiplici potentiarum animae, p. 2, cc. 17–19) and Roger Bacon (Quaestiones primae supra undecimum Primae Philosophiae Aristotelis, q. 100). The sixth view argues that the agent intellect is not merely a habit but a habitual potency that is constantly poised to abstract what is intelligible from the phantasm. However, it cannot act unless there is something in the internal sense powers from which it can abstract. On this view, the agent intellect does not have innate knowledge, but it does renders all intellectual knowledge intelligible. St. Bonaventure likens the agent intellect to the eye of a cat which, by its own intrinsic light, not only receives but makes the species within it.

The seventh and eight ways of understanding the agent and possible intellects are as an absolute potency and a relative potency. The seventh way argues that they are really one and the same power and differ only by comparison. The intellect is called “agent” when it is considered in itself and called “possible” when it is considered as united to the body and in relation to the imagination. This view was held by Richard Rufus (Scriptum super Metaphysicam XI, qq. 3–4). This view highlights the fact that intellectual knowledge is an act of the whole person. The eighth view insists that the agent and possible intellect are still two distinct intellects. The possible intellect is the intellect through which the soul is ordered to receive, and the agent intellect through which the soul is ordered to abstract.

These eight ways of understanding the relationship between the possible and agent intellects are not mutually exclusive. In fact, St. Bonaventure argues that the fourth, sixth, and eighth ways are all true. The agent and possible intellects both have active and passive aspects; the agent intellect is responsible for making the content of the imagination intelligible; the agent intellect is more absolute because it is through it that we are in act (In II Sent., d. 24, p. 1, a. 2, q. 4).

The will is the appetite or desire that follows upon the intellect. Aquinas argues that the will is an instance of a universal phenomenon in the created order. “A certain inclination,” he says,” follows upon every form” (Summa theologiae I, q. 80, a. 1). The inclination to hydrogen bonding follows upon the form of water, the inclination to put down roots follows upon the form of oak tree, and an inclination follows upon both sense and intellectual knowledge. The inclination from sense knowledge is called passion or emotion, and the inclination that follows upon intellectual knowledge is called will. The scope of a given inclination or appetitive power depends upon the scope of the form it follows. Natural appetites are invariably limited to one inclination. Passions are limited to one inclination, but that inclination can vary as our sense knowledge changes. Will, however, has the good in general as its object and thus is not limited to one inclination (Summa theologiae I, q. 83, a. 1).

Aquinas thinks this freedom of the will is compatible with necessity in certain circumstances. Although it is never compatible with an extrinsic coercion, it can be compatible with a necessity arising from the end or a natural and absolute necessity. Necessity of the end arises when a certain end cannot be attained (or at least not attained well) without one means. Thus, if I will to go to moon, I necessarily will a space ship since that is the only way to get there. The will for the moon necessarily leads to willing the spaceship. Natural and absolute necessity arises when the necessity arises from an intrinsic principle, either the matter or the form. For example, it follows by natural necessity that everything composed of contraries is corruptible, and it follows by natural necessity that a Euclidean triangle will have internal angles equal to 180 degrees. The will, St. Thomas argues, has a nature like everything else, and so by a natural and absolute necessity wills its final end (Summa theologiae I, q. 82, a. 1). Although it brings up many difficulties for the question of nature and grace, St. Thomas specifies that that end is the beatific vision since every other object is less than the universal good in general, and so does not fully move the will.{9} Therefore, a desire for God inspires every act of will that we have in this life, even if upon reflection we see that we willed something we should not have. Willing what we ought not is possible because our intellects cannot adequately judge a necessary connection between this present action and our ultimate end (Summa theologiae I, q. 82, a. 2).

He explains this position further by a distinction between the exercise of the will (willing or not-willing at all) and the determination of the will (willing a or non-a). No finite good fully determines the will, so our wills can be determined to them or to some other good. God alone fully determines the will, such that we are incapable of determining our will against him. This determination comes from the judgment of the intellect that a certain object is good (Summa theologiae I-II, q. 9, a. 1; Summa theologiae I-II, q. 10, a. 2). With regard to the exercise of the act, that is, with regard to having an act of will at all, St. Thomas says that the will moves itself to act insofar as God has established that it is naturally moved to its ultimate end (Summa theologiae I-II, q. 9, aa. 3, 5; On Evil, q. 6). Thus, if they have any act of will at all, the blessed in heaven are unable to will against God.

There were a handful of philosophers at this time who thought that the intellect does make the will act, namely Giles of Rome. This view was condemned explicitly in the Condemnations of 1270 and 1277. Thus, authors began to favor the will more than their predecessors. Scotus’s account of the will in some ways overlaps with Aquinas’s. He distinguishes a twofold freedom in the will. The will, which he identifies as a rational power, can do a or non-a, and it can also act or not act at all. This distinguishes the will from every natural power, which can only do one thing and always does it as much as it can (Questions on Aristotle’s Metaphysics IX, q. 15). Thus, the will is thoroughly contingent insofar as nothing makes it exercise an act of willing or nilling (i.e., willing against). The only way that the will can be said to be coerced is in the qualified sense that we can will things under certain circumstances that we would not otherwise will (Ordinatio IV, d. 29). He does not supply an example, but we can imagine that while a sailor would not normally will to throw the cargo overboard, he might do so if that were the only means of preventing the ship from sinking.

Scotus’s account of the will departs from Aquinas’s insofar as he makes use of St. Anselm’s distinction between an affection for justice (affectio iustitiae) and an affection for the advantageous (affectio commodi) (Anselm, On the Fall of the Devil, c. 14). Because of the affection for justice we have an innate liberty to be able to will some good not oriented to the self. Because of the affection for the advantageous, we always will with reference to ourselves. The affection for justice is nobler because to love something in itself is more an act of giving and thus a freer act. Scotus says that the affection for justice is perfected by the theological virtue of charity, and the affection for the advantageous is perfected by the theological virtue of hope (Ordinatio III, suppl., d. 46).

Scotus argues that, given this twofold affection within the will, our “natural will” is an inclination of the will, that is, a tendency by which it tends passively to receive what perfects it (Ordinatio III, d. 17). We naturally tend toward happiness, and not just happiness in general but the particular object that will really perfect the will (Ordinatio IV, suppl., d. 49, qq. 9–10, a. 1). However, the will does not necessarily will any good because such coercion would be contrary to the nature of the will. By its very nature, the will must always have that twofold liberty. In the face of an object that is thoroughly good with no aspect of evil whatsoever, our will could not hate or detest it (and thus, we cannot hate our own happiness), but the will fundamentally maintains its ability not to exercise any act at all (Ordinatio IV, suppl., d. 49, qq. 9–10, a. 2).

V. Epistemology

Philosophers in this period generally followed Aristotle’s account of knowledge. Knowledge begins in the external senses (sight, hearing, smell, touch, and taste). Since the thing sensed is not literally taken into the senses, authors argued that a certain form was received in the sense power, which they called a “sensible species.” The word species as it is used here refers not to a universal class of living things. Instead, it refers to the action of specifying the action of the sense power such that it comes to know this object instead of some other one. This sensible species is a likeness of the thing sensed by which the sensible thing acts on the knower (Deely, Intentionality and Semiotics, 23–25). After the sensation of the external senses, the common sense receives all the various objects and produces a single sense experience. Therefore, we do not know just white and round and sweet, but the sweet, white, round thing. The imagination, cogitative power, and memory then produce a phantasm from the objects of the common sense. Then, as discussed in the section on intellect above, the agent intellect abstracts what authors call the “intelligible species” from the phantasm, which is then received into the possible intellect. At this point, several divergences emerge among various authors. First, there is a debate over the existence of intelligible species, which also brings up what authors call an “interior word.” Second, there is a question of knowledge of individuals. Third, there is a question of certainty of knowledge.

Intelligible Species and Interior Word

This general account of knowledge is challenged by Peter John Olivi, who argues against the reality of intelligible species. Olivi rejects intelligible species entirely because he thinks the standard Aristotelian account of knowledge fails to account for the attention of the intellect. As a result, he posits a theory of direct attention by which our senses and intellect can become virtually present to some knowable thing “by the fact that the gaze of its power is so efficaciously directed to the thing as if it were really attaining it” (In II Sent., q. 58, ad 4). Thus, the cognitive power is the efficient cause of its own knowledge. Neither a species nor the thing known are efficient causes of knowledge, although the thing known is operative as the object and functioning as a final cause or, as he puts it, a terminative cause (In II Sent., q. 58, ad 14). Olivi thinks this external direction of the cognitive powers can occur by some sort of action at a distance (Jansen, Der Erkenntnislehre Olivis (Berlin, 1921), 118). Since the intellect virtually goes out to obtain knowledge by turning its attention to it, intelligible species are entirely to be rejected (See Pasnau, Theories of Cognition in the Later Middle Ages, 168–81).

Scotus comes to the defense of intelligible species by arguing that each intelligible species has two characteristics (passiones). By the first characteristic, the species exists as a quality in the knower and is thus an accident and a real attribute of the knower. The second characteristic occurs by the object as it shines forth again in the species (Reportatio Parisiensis I-A, d. 3, q. 4, n. 119). The second characteristic is clearly the more important for Scotus since by it the real attributes of the species hide themselves such that the object shines forth. Thus, even though the intelligible species exists subjectively and really in the knower, it is not that which is known. The thing known exists objectively through the second characteristic of the intelligible species and is that which we know. (See Scotus,Questions on Aristotle’s Metaphysics VII, q. 18, n. 51, and King, “Duns Scotus on Mental Content”).

In addition to intelligible species, many authors argue for the existence of an internal or mental word (verbum). The intelligible species is a form in the intellect, and the mental word is the expressed concept (or, sometimes, “understood intention”) of the object itself. As some later Thomists, (especially one 21st-century Thomist) argue, the mental word is a sign-vehicle which substitutes for and points toward the object known (Deely, What Distinguishes Human Understanding). As Aquinas argues, there are three things in the intellect: the intellectual power itself, the intelligible species of the thing understood, and the very act of understanding (intellection). But when we use vocal words like “stone,” we surely do not signify our intellectual power. We also do not understand our species because “stone” is not an intelligible species. An intelligible species is that by which (id quo) we understand, but we are not understanding by means of “stone.” Finally, we do not signify the very act of understanding because our act of understanding is not a stone. Thus, the spoken word “stone” must signify an interior word which we form when understanding. These interior words are “expressed, that is, formed in the soul” and they are compared to the intellect “not as that by which (quo) the intellect understands, but as that in which (in quo) it understands” (Commentary on the Gospel of John I, lect. 1, n. 25; Summa Contra Gentiles IV, c. 11; De veritate, q. 4, a. 1).

St. Thomas argues that we form these interior words with both the first act of the mind (knowing of “indivisible” essences) and the second act of the mind (judging). Henry of Ghent argues that “in every act of understanding, however small it be, it is necessary to form a word [verbum],” although he specifies that internal words are formed only in the second act of the mind, not the first (Quodlibet II, q. 6; Goehring, “Henry of Ghent on the Verbum Mentis”; Pini, “Henry of Ghent’s Doctrine of Verbum in its Theological Context”). The centrality of the interior word seems to go unnoticed by many.{10} Later medieval philosophers and theologians distinguish between an impressed intelligible species and an expressed intelligible species to refer to the intelligible species and the interior word, respectively.

Knowledge of Individuals

In the standard Aristotelian account of knowledge, when the agent intellect abstracts the essence from the phantasm, it does so precisely by leaving aside all the individualizing features of the phantasm (See, e.g., Aquinas, Summa theologiae I, q. 85, a. 1). In a similar vein, Jean de la Rochelle argues that “since it [the intellect] is an immaterial power, its object will be immaterial, and this is the intelligible” (Summa de anima, c. 113). This account has the advantage of explaining how the intellect knows universals, but also seems to make it impossible for us to know individuals intellectually. (i.e., We can know individuals by means of our senses, but not by intellect.)

Aquinas argues that while the intellect directly knows universals only, it still has an indirect access to individuals. As Aristotle says in De anima III, c. 7, we never think without a phantasm, which means that our intellectual considerations are accompanied by a phantasm in the internal sense powers. Therefore, our intellect returns or reflects back upon the phantasm. Because of this return to the phantasm, we do not merely have intellectual knowledge of man and sensitive knowledge of Socrates, but we can also have the intellectual knowledge necessary to form the proposition "Socrates is a man” (Summa theologiae I, q. 86, a. 1; q. 85, a. 7).

Scotus takes issue with this account for two reasons. First, he denies that the senses know individuals, and second, he argues that we can and do have direct intellectual knowledge of individuals through his distinction of intuitive and abstractive cognition. As for the first position, he argues that St. Thomas’s position is based on the principle that matter is the principle of individuation, which he claims was part of the Condemnations of 1277 (Questions on Aristotle’s De anima, q. 22, n. 12). In particular, it is included in the condemned proposition that there cannot be many individuals of the same species because of a defect of matter.{11} Moreover, he proposes a thought experiment. Suppose there are two identical statues. If we saw one of them in a certain place one day, and then came back the next day and saw an identical statue in the same place, we would not be able to determine whether we were seeing the same statue or its identical twin. But if our senses grasped individuals qua individual, then we would be able to know each of the identical statues distinctly. When we saw the white of the statue, we would not be seeing “white,” but rather this white as opposed to that white on the identical twin. Thus, we would not make the error (See Questions on Aristotle’s Metaphysics, q. 15, n. 20; q. 13, n. 158). Therefore, our senses do not know the individual differences of things in this life (Questions on Aristotle’s Metaphysics, q. 13, n. 158).

As for the second point, Scotus distinguishes between intuitive and abstractive cognition. In intuitive cognition, the object is known as present in existence; in abstractive cognition, the object is known without any reference to its existence or non-existence (Ordinatio I, d. 1, p. 1, q. 2, n. 35; Ordinatio II, d. 3, p. 2, q. 2, nn. 321). Although it might be easy to associate intuitive cognition with sense knowledge and abstractive knowledge with intellectual knowledge, Scotus insists that intuitive and abstractive cognition are found in both sensation and intellection. At the level of sense, the external and particular senses have intuitive cognition, and the imagination has abstractive cognition (Ordinatio II, d. 3, p. 2, q. 2, n. 323). At the level of intellect, we usually know by abstractive cognition, but he insists that we have intellectual intuitive cognition as well.

Scotus offers two arguments for intellectual intuitive cognition. Intuitive cognition is more perfect than abstractive cognition precisely because the existence in reality of the intelligible object is known (Ordinatio I, d. 2, p. 2, qq. 1–4, n. 394). But a higher power should not be lacking a perfection had by a lower power. Therefore, intellect, and not just the senses, should have intuitive cognition (Quodlibet, q. 6, nn. 18–19). Again, intellectual intuitive cognition is precisely the sort of cognition that everyone claims the blessed in heaven have of God’s essence. Their knowledge is intellectual and includes the direct knowledge of God’s existence, thus making it intuitive (Quodlibet, q. 6, n. 20).{12}

VI. Ethics

Aristotle argues in the Nicomachean Ethics that all our actions are oriented toward our perfect flourishing in happiness, which he called eudaimonia. All our actions are weighed against that happiness. Those actions which contribute to the attainment of happiness are good actions, and those which inhibit the attainment of happiness are bad actions. Thus, there are two primary questions to be asked in ethics: (1) in what does happiness consist? and (2) how is that ultimate good attained? Philosophers unanimously declare God as the answer to the first question. The second question is answered by the joining of a theory of natural law, by which we know what is good and to be done and what is bad and to be avoided, and a theory of virtue, whereby the law becomes internalized such that we begin to act more and more in accord with the natural law and with greater ease. For the sake of space, only Aquinas’s and Scotus’s theories will be examined briefly here.

Eudaimonism

Eudaimonism comes from the Greek word eudaimonia, which means happiness or human flourishing. An ethical theory of eudaimonism argues that our actions seek some good or other as the end or goal of the action. A little reflection reveals that those goals are for the sake of other (and usually greater) goods. And even those other goods are for the sake of other, greater goods. I seek anesthesia for the sake of surgery, and I seek surgery for the sake of health. But this series of goods for the sake of other goods cannot go on forever because such a series of goods is wholly motivated by the ultimate or best good in the series. If I don’t desire health, then not only do I not seek surgery, but I also do not seek anesthesia. So, there must be a first or ultimate good that motivates all the other goods that we pursue.{13}

Aquinas argues that there can be only one ultimate human good. If the ultimate good is to be ultimate, then it must be perfectly fulfilling. If there were many ultimate goods, then none of them would be perfectly fulfilling, and there would be no ultimate goods. Moreover, natures only tend toward one thing, so human nature and our will only tends toward one ultimate good.{14} This argument brings up the difficulty of nature and grace mentioned above in the discussion of the will and necessity in the section on Human Nature. Given the limited scope of this article, only two things should be mentioned about that issue here. First, this issue is raised by Christian authors as an expansion on Aristotle’s account of the will precisely because Aristotle did not yet conceive of a good like the Beatific Vision. Second, given that the Beatific Vision is, strictly speaking, beyond what our human nature is capable of and is therefore supernatural, there is a question of a natural end of man versus a supernatural end of man. Authors and interpreters dispute whether these are two distinct ends, two ends subordinated to one another, or just one supernatural end.

Given that we have one ultimate good, the next question is what that ultimate good is. People give diverse answers to this question: money, honor, fame, power, virtue, pleasure, contemplation, and so on (Aquinas, Summa theologiae I-II, q. 1, a. 7). Aquinas argues that no finite good can be our ultimate good because no finite good is unqualifiedly good. As noted above in the discussion of the will, our will has the good in general or universal good as its object. Since any finite good is less than the complete and universal good, our happiness cannot consist in a finite good. Only God is the ultimate, universal good, which means that our happiness consists in knowing and loving God (Aquinas, Summa theologiae I-II, q. 2, a. 8).

The discussion of eudaimonism makes it clear that our ethical life is about attainment of our ultimate end. And having determined what the ultimate end is, the next question is, what means do we employ to get there? Put another way, what actions lead to the ultimate end and which do not? The actions that lead to the ultimate end are morally good and the ones that do not are morally bad, but how can we determine which is which? Philosophers appeal to both a theory of natural law and a theory of virtue for answers to these questions. Both Aquinas and Scotus deploy both theories.

VII. Conclusion

Medieval philosophy from ca. 1225–1308 was marked by a flowering and advancing of inquiry. The rise of the university, an influx of texts, and the exceptional thinkers of the time all made this period one of the richest in speculation in all of history. For all the many disagreements between them, they were all, broadly speaking, followers of Aristotle with many Platonic influences, and they all emphasized the importance of metaphysics, the harmony of faith and reason, the unity and integrity of the human person, our capacity for truth, and the importance of the moral life. Their rigorous thought will continue to be an exceptional source of speculation.