Problem of universals  

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"I shall omit to speak about genera and species, as to whether they subsist (in the nature of things) or in mere conceptions only; whether also if subsistent, they are bodies or incorporeal, and whether they are separate from, or in, sensibles, and subsist about these, for such a treatise is most profound, and requires another more extensive investigation". --Porphyry on the problem of universals in the Isagoge, translation by Boethius, English translation quoted in A History of Western Philosophy (McInerny and Caponigri)

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In metaphysics, the problem of universals refers to the question of whether properties exist, and if so, what they are. Properties are qualities or relations that two or more entities have in common. The various kinds of properties, such as qualities and relations are referred to as universals. For instance, one can imagine three cup holders on a table that have in common the quality of being circular or exemplifying circularity, or two daughters that have in common being the daughter of Frank. There are many such properties, such as being human, red, male or female, liquid, big or small, taller than, father of, etc.

While philosophers agree that human beings talk and think about properties, they disagree on whether these universals exist in reality or merely in thought and speech.



The main positions on the issue are generally considered to be: realism, nominalism, and idealism (sometimes simply called "anti-realism" with regard to universals).


The realist school claims that universals are real — they exist and are distinct from the particulars that instantiate them. There are various forms of realism. Two major forms are Platonic realism (universalia ante res) and Aristotelian realism (universalia in rebus). Platonic realism is the view that universals are real entities and they exist independent of particulars. Aristotelian realism, on the other hand, is the view that universals are real entities, but their existence is dependent on the particulars that exemplify them.

Realists tend to argue that universals must be posited as distinct entities in order to account for various phenomena. For example, a common realist argument, arguably found in Plato, is that universals are required for certain general words to have meaning and for the sentences in which they occur to be true or false. Take the sentence "Neil Young is a musician". The realist may claim that this sentence is only meaningful and expresses a truth because there is an individual, Neil Young, who possesses a certain quality, musicianship. Thus it is assumed that the property is a universal which is distinct from the particular individual who has the property.


Nominalists assert that only individuals or particulars exist and deny that universals are real (i.e. that they exist as entities or beings). The term "nominalism" comes from the Latin nomen ("name"), since the nominalist philosopher agrees that we predicate the same property of multiple entities but argues that the entities only share a name, not a real quality, in common. There are various forms of nominalism (which is sometimes also referred to as "terminism"), three major forms are resemblance nominalism, conceptualism, and trope nominalism. Nominalism has been endorsed or defended by many, including William of Ockham, Peter Abelard, D. C. Williams (1953), David Lewis (1983), and arguably H. H. Price (1953) and W. V. O. Quine (1961).

Nominalists often argue for their view by claiming that nominalism can account for all the relevant phenomena, and therefore—by Occam's razor or some sort of principle of simplicity—nominalism is preferable, since it posits fewer entities. Whether nominalism can truly account for all of the relevant phenomena is debated.


Idealists, such as Kant and Hegel, posit that universals are not real, but are ideas in the mind of rational beings. Idealists do not reject universals as arbitrary names; rather, they treat universals as fundamental categories of pure reason (or as secondary concepts derived from those fundamental categories). Universals, in idealism, are intrinsically tied to the rationality of the subject making the judgment.

For instance, when someone judges that two cup holders are both circular they are not noticing a mind-independent thing ("circularity") that is in both objects, nor are they simply applying a name ("circular") to both. Rather, they partially constitute the very concept of cup holder by supplying it with the concept of circularity, which already exists as an idea in their rational mind.

Thus, for idealists, the problem of universals is only tangentially a metaphysical problem; it is more of a problem of psychology and epistemology.

Ancient thought


Plato believed there to be a sharp distinction between the world of perceivable objects and the world of universals or forms: one can only have mere opinions about the former, but one can have knowledge about the latter. For Plato it was not possible to have knowledge of anything that could change or was particular, since knowledge had to be forever unfailing and general. For that reason, the world of the forms is the real world, like sunlight, the sensible world is only imperfectly or partially real, like shadows. This Platonic realism, however, in denying that the eternal Forms are mental artifacts, differs sharply with modern forms of idealism.

One of the first nominalist critiques of Plato's realism was that of Diogenes of Sinope, who said "I've seen Plato's cups and table, but not his cupness and tableness."


Plato's student Aristotle disagreed with his tutor. Aristotle transformed Plato's forms into "formal causes", the blueprints or essences of individual things. Whereas Plato idealized geometry, Aristotle emphasized nature and related disciplines and therefore much of his thinking concerns living beings and their properties. The nature of universals in Aristotle's philosophy therefore hinges on his view of natural kinds.

Consider for example a particular oak tree. This is a member of a species and it has much in common with other oak trees, past, present and future. Its universal, its oakness, is a part of it. A biologist can study oak trees and learn about oakness and more generally the intelligible order within the sensible world. Accordingly, Aristotle was more confident than Plato about coming to know the sensible world; he was a prototypical empiricist and a founder of induction. Aristotle was a new, moderate sort of realist about universals.

Medieval thought


The problem was introduced to the medieval world by Boethius, by his translation of Porphyry's Isagoge. It begins:

"I shall omit to speak about genera and species, as to whether they subsist (in the nature of things) or in mere conceptions only; whether also if subsistent, they are bodies or incorporeal, and whether they are separate from, or in, sensibles, and subsist about these, for such a treatise is most profound, and requires another more extensive investigation".

Duns Scotus

Duns Scotus argued strongly against both nominalism and conceptualism, arguing instead for Scotist realism, a medieval response to the conceptualism of Abelard.


William of Ockham argued strongly that universals are a product of abstract human thought. According to Ockham, universals are just words/names that only exist in the mind and have no real place in the external world.

Medieval realism

Realism was argued for by both Thomas Aquinas and John Duns Scotus. Aquinas argued that both the essence of a thing and its existence were clearly distinct, in this regard he is close to the teaching of Aristotle. Scotist realism argues that in a thing there is no real distinction between the essence and the existence, instead there is only a Formal distinction. Both these opinions were denied by Scotus' pupil William of Ockham.

Medieval nominalism

Nominalism was first formulated as a philosophical theory in the Middle Ages. The French philosopher and theologian Roscellinus (c. 1050-c. 1125) was an early, prominent proponent of this view. It can be found in the work of Peter Abelard and reached its flowering in William of Ockham, who was the most influential and thorough nominalist. Abelard's and Ockham's version of nominalism is sometimes called conceptualism, which presents itself as a middle way between nominalism and realism, asserting that there is something in common among like individuals, but that it is a concept in the mind, rather than a real entity existing independently of the mind. Ockham argued that only individuals existed and that universals were only mental ways of referring to sets of individuals. "I maintain", he wrote, "that a universal is not something real that exists in a subject... but that it has a being only as a thought-object in the mind [objectivum in anima]". As a general rule, Ockham argued against assuming any entities that were not necessary for explanations. Accordingly, he wrote, there is no reason to believe that there is an entity called "humanity" that resides inside, say, Socrates, and nothing further is explained by making this claim. This is in accord with the analytical method which has since come to be called Ockham's razor, the principle that the explanation of any phenomenon should make as few assumptions as possible.

Critics argue that conceptualist approaches only answer the psychological question of universals. If the same concept is correctly and non-arbitrarily applied to two individuals, there must be some resemblance or shared property between the two individuals that justifies their falling under the same concept and that is just the metaphysical problem that universals were brought in to address, the starting-point of the whole problem (MacLeod & Rubenstein, 2006, §3d). If resemblances between individuals are asserted, conceptualism becomes moderate realism; if they are denied, it collapses into nominalism.

Modern and contemporary views


George Berkeley, best known for his empiricism, was also an advocate of an extreme nominalism. Indeed, he disbelieved even in the possibility of a general thought as a psychological fact. It is impossible to imagine a man, the argument goes, unless one has in mind a very specific picture of one who is either tall or short, European, African or Asian, blue-eyed or brown-eyed, et cetera. When one thinks of a triangle, likewise, it is always obtuse, right-angled or acute. There is no mental image of a triangle in general. Not only then do general terms fail to correspond to extra-mental realities, they don't correspond to thoughts either.

Berkeleyan nominalism contributed to the same thinker's critique of the possibility of matter. In the climate of English thought in the period following Isaac Newton's major contributions to physics, there was much discussion of a distinction between primary qualities and secondary qualities. The primary qualities were supposed to be true of material objects in themselves (size, position, momentum) whereas the secondary qualities were supposed to be more subjective (color and sound). But on Berkeley's view, just as it is meaningless to speak of triangularity in general aside from specific figures, so it is meaningless to speak of mass in motion without knowing the color. If the color is in the eye of the beholder, so is the mass.

Berkeley's great contribution (picked up on later by Kant) was to suggest the preposterousness of referencing absolute knowledge, given that all knowledge is gained through contingent sensory experience. In fact, the very notion of finding coherence and permanence within sensory experience was so preposterous to him, that he had to postulate the notion of a God who holds all reality in HIS mind, in order to explain why the world doesn't just vanish when we stop perceiving it. He was forced, by his extreme empiricism, to posit the existence of God in order to explain our experience of coherence, even though on an empirical understanding of raw sense data, such a conclusion did not follow. In this, he demonstrates the importance and brilliance of Kant's "Copernican revolution" in epistemology that was to follow. For without Kant, Berkeley was not able to give an account of the coherence of our experience that squared with his empiricism. David Hume tried to give such an account when he proposed that concepts are merely the faded memories of sensory experiences had over and over again, like writing on a page which eventually sinks through to the underlying pages. But this account seemed to threaten the very possibility of science as an objective endeavor and made Kant, himself a scientist, very uneasy. It forced Kant to come up with his theory of noumenal objects as unverifiable but understandable extensions of our immediate sensory experience constructed according to the inherent schemae of our understanding. Thus, in place of God's role as guarantor of the coherence of the world, Kant posits a faculty of reason structured by the forms of our intuition (our sense of time and space) and the categories of our understanding (like the notion of cause and effect).


Idealism is a broad category that includes several diverse themes, from Kant's radical doubt about what can truly be perceived externally to Hegel's Absolute Ideal as the verification of the sum of potential manifestations of matter and concepts. This position argues that the nature of reality is based only in our minds or ideas, and represents one of several divergent interpretations of Kant’s legacy. On Hegel’s view, the external world is inseparable from the mind, consciousness or perceptions. Universals are real and exist independently of that on which they might be predicated.

But to conflate Kant's and Hegel's versions of idealism is to seriously miss the point of Kant’s radical doubt, which was stimulated in turn by David Hume's. Kant claimed it was Hume’s skepticism about the nature of inductive reasoning and the conclusions of rationalist metaphysicians (Descartes, Spinoza, Leibniz) that "roused him from his dogmatic (i.e. rationalist) slumbers" and spurred him on to one of the most far reaching re-evaluations of human reason since Aristotle. Following Aristotle’s lead, Kant considered that knowledge can only be had through experience of particulars. Given that premise, the notion of absolute knowledge (as described by Plato and the rationalists) is seen as mere illusion, and this is what he set out to demonstrate in the first part of his magnum opus "The Critique of Pure Reason" (1781). He claims to demonstrate that because knowledge can only be had through contingent (imperfect) experience, the notion of absolute, uncontingent knowledge must not actually be obtainable, but must function merely as a “regulative principle” or heuristic device for problem solving. Thus we can conceive of a “noumenal” world (noumenal meaning "object of thought") which exists only as a heuristic for our cognitive capacities and not as something directly accessible to experience. The noumenal world for Kant is the way “things in themselves” might appear to a being of uncontingent reason (i.e. “God”).

The “phenomenal” world, on the other hand is the world of experience, in which we live and in which objects are given to reason in experience. Our understanding of the phenomenal world is inevitably “colored” by the imperfections, or restrictions, of the knowing apparatus, and this is what he set out to describe in the first part of the 1st Critique. Following Aristotle’s lead, he describes categories of the understanding, such as the notion of cause and effect, which inevitably mediate our experience of the world and give us the objects of our experience. The objects “in themselves” as they might appear in their “universal” or “absolute” nature are forever hidden from us, and thus Kant effectively rules out the type of access to the world of the forms that had been formulated by Plato. The notion of the noumenal can only function as a heuristic of reason, not as an actual something to be experienced by contingent beings. Thus Kant effects his “Copernican” revolution of knowledge by changing our perspective on knowledge from a question of “what can truly be known” (i.e. how can we actually come to know universals), to a question of “how does the knowing mind operate.” As with Copernicus, the data remains the same but the model used to encounter the data shifts tremendously.

After Kant, the problem of universals becomes a problem of human psychology and questions about conceptual models we use to understand universals, rather than the same old metaphysical arguments about what universals “really” are. The second part of the 1st Critique is Kant’s examination of the rationalist claims to absolute knowledge, taking on the most famous of these, the ontological proof of God’s existence, and showing that he can, through pure, non-experiential logic, both prove the affirmative and the negative of a proposition about a “noumenal object” (i.e. an object like “God” which can never be an object of direct experience for a contingent being). Given that both A and not-A are seen to be “true,” Kant concludes that it’s not that “God doesn’t exist” but that there is something wrong with how we are asking questions about God and how we have been using our rational faculties to talk about universals ever since Plato got us started on this track! He goes on, in subsequent Critiques and other works, to demonstrate his model for the proper use of concepts like “God” “the Good,” and “the beautiful,” effecting the most radical re-evaluation of these ideas since Plato, and changing forever the course of western philosophy. It is perhaps no small exaggeration to claim that most western philosophers since Kant, even if they disagree with him, have had to find some way to respond to his revolutionary ideas.


John Stuart Mill discussed the problem of universals in the course of a book that eviscerated the philosophy of Sir William Hamilton. Mill wrote, "The formation of a concept does not consist in separating the attributes which are said to compose it from all other attributes of the same object and enabling us to conceive those attributes, disjoined from any others. We neither conceive them, nor think them, nor cognize them in any way, as a thing apart, but solely as forming, in combination with numerous other attributes, the idea of an individual object".

However, he then proceeds to state that Berkeley's position is factually wrong by stating the following:

But, though meaning them only as part of a larger agglomeration, we have the power of fixing our attention on them, to the neglect of the other attributes with which we think them combined. While the concentration of attention lasts, if it is sufficiently intense, we may be temporarily unconscious of any of the other attributes and may really, for a brief interval, have nothing present to our mind but the attributes constituent of the concept.

In other words, we may be "temporarily unconscious" of whether an image is white, black or yellow and concentrate our attention on the fact that it is a man and on just those attributes necessary to identify it as a man (but not as any particular one). It may then have the significance of a universal of manhood.


The 19th-century American logician Charles Sanders Peirce, known as the father of pragmatism, developed his own views on the problem of universals in the course of a review of an edition of the writings of George Berkeley. Peirce begins with the observation that "Berkeley's metaphysical theories have at first sight an air of paradox and levity very unbecoming to a bishop". He includes among these paradoxical doctrines Berkeley's denial of "the possibility of forming the simplest general conception". He wrote that if there is some mental fact that works in practice the way that a universal would, that fact is a universal. "If I have learned a formula in gibberish which in any way jogs my memory so as to enable me in each single case to act as though I had a general idea, what possible utility is there in distinguishing between such a gibberish... and an idea?" Peirce also held as a matter of ontology that what he called "thirdness", the more general facts about the world, are extra-mental realities.


William James learned pragmatism, this way of understanding an idea by its practical effects, from his friend Peirce, but he gave it new significance. (Which was not to Peirce's taste - he came to complain that James had "kidnapped" the term and eventually to call himself a "pragmaticist" instead). Although James certainly agreed with Peirce and against Berkeley that general ideas exist as a psychological fact, he was a nominalist in his ontology:

From every point of view, the overwhelming and portentous character ascribed to universal conceptions is surprising. Why, from Plato and Aristotle, philosophers should have vied with each other in scorn of the knowledge of the particular and in adoration of that of the general, is hard to understand, seeing that the more adorable knowledge ought to be that of the more adorable things and that the things of worth are all concretes and singulars. The only value of universal characters is that they help us, by reasoning, to know new truths about individual things.|William James|The Principles of Psychology

There are at least three ways in which a realist might try to answer James' challenge of explaining the reason why universal conceptions are more lofty than those of particulars - there is the moral/political answer, the mathematical/scientific answer and the anti-paradoxical answer. Each has contemporary or near contemporary advocates.

The moral or political response is given by the conservative philosopher Richard M. Weaver in Ideas Have Consequences, where he describes how the acceptance of "the fateful doctrine of nominalism" was "the crucial event in the history of Western culture; from this flowed those acts which issue now in modern decadence".

Roger Penrose contends that the foundations of mathematics can't be understood absent the Platonic view that "mathematical truth is absolute, external and eternal, and not based on man-made criteria ... mathematical objects have a timeless existence of their own..."

Nino Cocchiarella (1975), professor emeritus of philosophy at Indiana University, has maintained that conceptual realism is the best response to certain logical paradoxes to which nominalism leads. It is noted that in a sense Cocchiarella has adopted Platonism for anti-Platonic reasons. Plato, as seen in the dialogue Parmenides, was willing to accept a certain amount of paradox with his forms. Cocchiarella adopts the forms to avoid paradox.


The Australian philosopher David Malet Armstrong has been one of the leading realists in the twentieth century, and has used a concept of universals to build a naturalistic and scientifically realist ontology upon. In both Universals and Scientific Realism and Universals: An Opinionated Introduction, Armstrong describes the relative merits of a number of nominalist theories which appeal either to "natural classes" (a view he ascribes to Anthony Quinton), concepts, resemblance relations or predicates, and also discusses non-realist "trope" accounts (which he describes in the Universals and Scientific Realism volumes as "particularism"). He gives a number of reasons to reject all of these, but also dismisses a number of realist accounts.

See also

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