Nominalism is a metaphysical theory about what kinds of things exist. Its answer is that, strictly speaking, there are no kinds of things at all—only individuals that resemble one another in various ways. On the nominalist view, what we call a “kind” or “species” is not something real and shared among individuals but simply a common name (in Latin, nomen) assigned to a group of individuals on the basis of their resemblances. Nominalism rose to prominence in the late medieval period with thinkers like William of Ockham and Jean Buridan, and it denies the existence of the universals and common natures affirmed by the older realist tradition. Though it has receded as an explicit philosophical position, an implicit nominalism remains pervasive in the late modern world, shaping how most people today think about knowledge, science, and what it means to understand things as they are. It also leads to problematic positions in moral science as well as in theological reflection.
To study slime molds, we would first need to know what kind of thing a slime mold is. Are slime molds plants, animals, or fungi? We would need at least some sense of the whole subject matter that contains slime molds. Once we know that slime molds are microorganisms (protists, to be precise) and not fungi, plants, or animals, we know that our questions about slime molds belong to microbiology.
For a question like “What is nominalism?” we similarly need some sense of the whole subject matter in question. Nominalism is a theory about what exists—a broad theory with implications for almost everything. Just as we can ask what discipline treats numbers (mathematics) or what discipline treats stars (astronomy), we can ask what discipline treats something as broad as existence. The answer is the discipline that studies everything in the most general possible way, that studies what existence and being are and how things exist: metaphysics, the science of being.
Any metaphysics will have to discuss both individual things and kinds of things. An individual thing is something that we can point to and that exists in a place at a time. Usually, we can refer to individual things by saying “this thing here.” Examples are this cat, this pen in that bag, this elm tree behind your house, and so on. A kind of thing, by contrast, is something common to many individual things, something that has many instances. Cat is a kind of thing common to many individual mammals (namely, all the cats); tree is a kind of thing common to many individual living things (namely, all the trees).
So, on the nominalist account, what kinds of things exist? The nominalist answer is this: there are no kinds of things. There are no things common to many individuals. If we take cat as an example, there is nothing like cat as a kind of thing; there are only individual animals that resemble one another in the way we call “cats.”
But what about the fact that cats seem clearly to be one kind of thing, as opposed to dogs, which are another? The nominalist admits that there do seem to be kinds of things in this way, but he denies that kinds of things really exist as something shared or common to individuals. Nominalists say that, when we speak of kinds of things, we really just mean groups of individuals that somehow resemble each other. These resemblances are not due to something that the individual things have in common; in particular, the resemblances among cats are not due to the fact that they all belong to the cat species. There is no “cat-sameness” among them.
These resemblances can be used to demarcate kinds of things, and we can then give those demarcated groups a common name, such as “cat.” In the nominalist view, that is all a “kind of thing” is: a name for things that resemble each other. (The Latin word for “name” is nomen, which is the source of the term “nominalism.”) Cats are justifiably called “cats” only because they maximally resemble each other, and that is why we refer to them with a common name—in this case, “cat.”
How can we come to know anything if there is nothing common or shared among different things? The nominalist might say that what our mind does is note resemblances in the things we experience; we have many experiences, and our mind forms a concept of how the things we experience resemble each other and how they do not. When we think of cats, our mind employs its concept of cats, but that concept is just something the mind has formed from resemblances it has seen among certain things we have learned to call by the name “cats.”
Nominalists such as the medieval friar William of Ockham said that this way of forming a concept is enough for us to know natural things in our experience in an ordinary human way. Other nominalists, such as Jean Buridan, developed precise theories about how we can truly form universal concepts on the basis of resemblances alone, as well as accounts of how we can speak of general features of things and come to know them without having to say that there are kinds or common natures in the things themselves. Nominalists will also say that this does not mean we can know the natures of things themselves; we know the natures of things only insofar as we know things as individuals, not as common natures or species. They will agree that we do not know the natures of things in themselves as something different individuals have in common, because that would imply that things of a certain kind share a common nature or essence—one that can ground our judgments about them—and that is precisely what nominalism denies. According to the nominalist, there are no such natures. All we can ever do is comprehend individuals based on resemblances to other individuals. But that, nominalists say, is just what human knowledge is. Nominalists will insist that this is real, even certain, knowledge.
If there are no natures of things, then how can we speak about something as good or bad for us as humans? How can we think of one thing as right and another thing as wrong? Many nominalists will say that good and bad, right and wrong, are not related to our nature or something about us that makes us human; they will say right and wrong are entirely given by the will of God. Some even take this to an extreme conclusion: William of Ockham said that, if God had commanded murder, then murder would be right. This seems a bizarre claim, but consider this: if we say that God commands us to act according to our nature, then God’s commands must be in accord with our nature, and that seems to make nature somehow superior to God and to His will for us. The nominalist insists that God’s pure and undetermined will is the source of everything, even of creation itself; and, therefore, good and bad, right and wrong are completely determined by that same divine will. And in the realm of moral theology, where the Church teaches that God gives us grace so that we can follow Him, the nominalists will say that what God gives us is simply His own acceptance of us. God does not give us anything real that can change how we act; rather, God accepts us and simply takes us as righteous, even though we are not. This kind of claim will be familiar to many Protestants, since it is how early reformers like Luther understood grace.
There are many ways to object to nominalism and many reasons to reject it. Here are four, simply stated.
First, there really do seem to be different kinds of things in the world, not just individual things that sometimes resemble each other and sometimes do not. This is a fundamental disagreement nominalists have with many others, at the level of first principles. The claims of nominalists to explain this all away are said to be failures, and ultimately the ordinary human conviction that there are different kinds of things in the world is taken to be stronger than any nominalist claims.
Second, nominalism cannot explain how things have certain possibilities and potentialities. It is clear, for example, that the heart is not just an individual thing that happens to pump blood in many animals; rather, the heart is something that pumps blood because of what it is, because of its valves, structure, ventricles, and use of muscle contraction—all intimately connected with the motion of blood in the body. There seems to be nothing within just individual things taken as individuals that can account for all the potentialities of things like this.
Third, the knowledge that is possible for us does seem to be far more than just a knowledge of resemblances. For example, think of proofs in geometry—that a triangle inscribed in a semicircle is always a right triangle, say. We can truly come to know these proofs and why they are proofs: that is, what the causes are that make things to be this way. It is true, however, that our knowledge does not perfectly extend to knowing every detail of most natural things, and the natures of many things are hard for us to discover.
Fourth, nominalists say that we form our concepts by abstracting from the resemblances we see in things. But what precisely constitutes a resemblance? First, how do we know that in respect of which one thing resembles another? Without positing something like a nature, it is hard to see how the nominalists can account for what the resemblance is a resemblance of. Second, how do we differentiate degrees of resemblance? This is especially relevant since two things can resemble one another in many ways, and it is hard to see how the nominalist can differentiate between those ways in order to select some for use in abstracting to the concept.
Nominalism matters because it is everywhere in the late modern world. An implicit nominalism lies behind how most people in our time think. Most people do not think that we can truly come to understand things in themselves. Most people think that the mind works mainly by gathering a set of experiences for how things might resemble each other and collating them. This implicit nominalism is deepened in many modern disciplines because the natural sciences often speak in nominalistic ways—for example, that no theory can ever be fully proved, or that empirical science is the highest form of knowledge.
Nominalism is highly problematic as a foundation for understanding existence and existing things since it rejects the universals and natures that are genuinely in things and make things to be what they are. Because of that, nominalism does not allow us to reach the truth about how things in the world really are, but only the truth about how things appear based on their resemblances to other things. Knowing how things seem to be is not enough for knowing them as they are in themselves.
Timothy Kearns is Professor of Western Civilization and Writing at the Legion of Christ College of Humanities in Cheshire, Connecticut.
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