Universal and Particular

Plato's theory of Forms is the first systematic answer to the problem of universals, and it remains the most radical. When Socrates asks "what is virtue?" he seeks a single thing (virtue itself) that is shared by all virtuous actions. Plato concludes that this universal must be real: not merely a concept in the mind, not merely a word that covers many things, but an actually existing object that the particular virtuous actions approximate by "participating" in it.

The Forms are eternal, unchanging, and accessible only to reason, not to sense. Particular beautiful things are beautiful because they participate in Beauty Itself. But they are always becoming, always mingling beauty with its opposite; they are not beauty without qualification. Only the Form of Beauty is beautiful without qualification. The ascending line of the Republic (from imagination through belief through reason to pure intellect) traces the philosopher's path from particulars to universals.

The separation of universals from particulars is the contested move. Aristotle will argue that it creates an unnecessary ontological doubling: if there is already a human being, why posit Human Itself? And the "third man" regress threatens: if particular men and the Form of Man are similar, there must be a third man that they share, and so on to infinity. Plato engages this difficulty in the Parmenides but does not resolve it to everyone's satisfaction.

Plato establishes the extreme realist position (universals exist separately and are more real than particulars) that sets the terms for all subsequent debate. Aristotle will argue that separate Forms solve nothing and generate a regress; Aquinas will try to save the insight by locating the Forms in the divine mind rather than a separate realm; and the nominalists will eventually ask whether any of this machinery is needed at all.

Aristotle's critique of Plato's theory of Forms is the most influential in the tradition. The Forms, separately existing in some transcendent realm, fail to explain what they were meant to explain. If particulars are intelligible because they participate in Forms, and if participation means resemblance, then we need a third thing to explain how the particular and the Form are similar, and so on to infinity. The theory multiplies entities without explaining anything.

Aristotle's alternative: universals are real, but they exist only in particular things. The form of man is not a separate object existing apart from Socrates and Callias; it is immanent in each of them, abstracted by the intellect when it considers many individuals and recognizes their common nature. The universal is "one over many" but is so only as an object of thought, not as a separately existing thing.

This is "moderate realism." The universal is neither a Platonic Form (separate and independently existing) nor a mere name (nothing in reality corresponding to it). It is a real feature of things, present in the things themselves and grasped by the intellect in the act of abstraction. Science is about universals because it seeks to state what is necessarily and universally true; but universals only exist in the particulars that instantiate them.

Aristotle's moderate realism becomes the standard Scholastic position. But the difficulty he leaves unresolved — how a single form can be wholly present in each of indefinitely many particulars without being divided among them — is precisely what William of Ockham will seize on in the fourteenth century, arguing that no such form exists and that only individual things are real.

Aquinas synthesizes the medieval debate about universals by distinguishing three modes of existence. Before things (ante rem): universals exist in the divine mind as exemplars of creation, this is the Platonic element. In things (in re): universals exist as the real forms of particular things, this is Aristotle's moderate realism. After things (post rem): universals exist in the human intellect as abstracted concepts, this is the contribution of Avicenna and the Peripatetic tradition.

These three modes are not competing theories but aspects of a single reality viewed from different perspectives. God knows the form of man as an eternal archetype. Each human being is man by virtue of instantiating that form. The human intellect grasps man as a universal by abstracting the form from its individual instantiations. Each level is real; none is the only reality.

The process of abstraction is central to Aquinas's account. The intellect "illuminates" the phantasm (the sensory image stored in memory) by stripping away its individual, material features (this particular height, weight, color) and grasping what is essential and universal. The result is the intelligible species, which is neither Socrates nor humanity in the abstract but the form of humanity that Socrates instantiates.

Aquinas's tripartite account is the definitive Scholastic synthesis. When William of Ockham attacks it in the fourteenth century (arguing that only individuals exist and universals are merely names), the Scholastic synthesis fractures. Hobbes, Locke, Hume, and Berkeley inherit the nominalist tradition; the realist tradition survives, in different forms, in Leibniz and Kant.

Hobbes is the most thoroughgoing nominalist in the tradition. "Of names," he writes, "some are proper, and singular to one thing only... and some are common to many things." A universal name like "man" or "stone" is a name given to many things in virtue of their resemblance to one another. But the resemblance is in the mind of the name-giver, not in the things. "There is nothing in the world universal but names, for the things named are every one of them individual and singular."

This nominalism has a polemical target: the Scholastic tradition that posited abstract entities corresponding to universal terms. For Hobbes, abstract entities like "human nature" or "the essence of man" are verbal creations, products of language, not discoveries about the world. The entire dispute over whether universals exist "before things," "in things," or "after things" is a dispute about words.

Hobbes's nominalism is also a critique of the Aristotelian-Scholastic sciences. If universals are only names, then definitions are only conventions and the knowledge produced by demonstrative science is knowledge only of the implications of our own definitions, not of the nature of things. This consequence (that science is a system of verbal conventions) will be resisted by Leibniz and Kant, who argue that the universal concepts employed in science cannot be merely nominal.

Hobbes's nominalism sets the parameters for the empiricist treatment of universals. Locke will refine it (distinguishing nominal from real essence); Berkeley will attack abstract general ideas; Hume will reduce universals to collections of similar particulars held together by custom. Against this nominalist tradition, Kant's categories will represent a new attempt to ground universal and necessary concepts.

Locke occupies a middle position between Aristotle's moderate realism and Hobbes's pure nominalism. General terms do not correspond to mere names without any mental correlate. The mind forms abstract general ideas by taking a particular idea (this particular triangle, this particular man) and removing its individual features, leaving only what is common to all members of the class. The abstract general idea of man includes figure, motion, and reason but excludes this particular height and complexion.

This process of abstraction is a genuine activity of the understanding, not just the assignment of names. But the result (the abstract idea) is not a Platonic Form existing outside the mind; it is a mental construction. Abstract general ideas are instruments for sorting and communicating, not discoveries of independently existing universals.

Locke's account generates a famous objection. Can the mind actually form an abstract idea of triangle, one that is neither equilateral, isosceles, nor scalene, yet all three at once? He claims it can. The abstract triangle is not any particular kind of triangle but an idea that has the features common to all. Berkeley will attack this as psychologically impossible: one cannot form an idea of a triangle that is no particular triangle at all.

Locke's account of abstract general ideas is the target of Berkeley's attack and Hume's revision. But Locke's fundamental insight (that general terms require something in the mind to back them up, even if not separately existing universals) is accepted by virtually all subsequent empiricists.

Berkeley attacks Locke's theory of abstract general ideas as the source of the greatest errors in philosophy. The abstract idea of triangle (neither equilateral, nor isosceles, nor scalene, yet all three) is a psychological impossibility. One cannot actually form such an idea; one can only name it. Abstract general ideas are not genuine mental entities but verbal fictions, which philosophers have treated as ideas and then been puzzled when they could not find them in their minds.

His alternative: the general idea of triangle is really just a particular triangular idea, some specific triangle that happens to be chosen as representative. When we prove something about triangles in general, we prove it about a particular triangle that is taken as standing in for all triangles of the same kind. The universality is in the use, not in the idea. General terms denote particular ideas that function as representatives of their class.

This account is simpler than Locke's and avoids the absurdity of impossible ideas. But it faces its own difficulty: what makes a particular idea representative of others? Berkeley's answer is that it represents all other ideas similar to it in the relevant respects. But this reintroduces the question of similarity, which is itself a general concept, a difficulty Berkeley does not fully dissolve.

Berkeley's critique of abstract ideas is influential partly because it is directed against Locke's version of abstraction and partly because it leads naturally to the question Hume will push further: what is the ultimate basis for the unity of a class? If there are only particular ideas and names, what justifies applying the same name to many particulars?

Hume agrees with Berkeley that there are no abstract general ideas: every idea is a particular. But he goes beyond Berkeley in explaining how general terms work without invoking even a "representative" particular idea as the stable bearer of meaning. The key is custom: through repeated experience of similar things, the mind forms a habit of associating the general name with any particular that falls in the relevant class.

When we hear the word "triangle," the mind revives a particular triangular idea, but the habit of association with all other similar ideas is simultaneously activated. If someone were to use "triangle" in a way that excluded equilateral triangles, the resemblance to equilateral triangles stored in memory would immediately trigger recognition of the misuse. The "universal" is not an abstract idea but a habitual readiness to apply the term to any sufficiently similar particular.

Hume's account is psychologistic in a way that later logicians will resist: it grounds the generality of terms in a mental habit rather than in any feature of things or in the formal properties of concepts. But it captures something important: the use of general terms is a skill acquired through practice and sustained by association, not the deployment of a pre-formed abstract content.

Hume's account of generality is the most completely nominalist in the tradition that still preserves some role for resemblance. Kant will argue that resemblance itself is not given in experience but is constituted by the understanding, so that the categories are needed even for the most basic act of grouping particulars under a common concept.

Kant argues that Hume's account of generality fails at the critical point. Hume grounds the use of general terms in habits of association formed by resemblance. But resemblance itself is a relation, and to recognize two things as resembling each other is already to subsume them under a common concept. The most basic act of grouping particulars together already presupposes the use of universal concepts.

The pure concepts of the understanding (the categories) are universal and a priori: they apply necessarily to all experience, not because they are derived from experience but because they are the conditions under which experience is possible. Substance, causality, community, reality, negation: these are the most fundamental categories by which the mind organizes the manifold of intuition into experience of objects.

The schema of each category explains how a pure concept applies to sensible particulars. The schema of substance is permanence in time: a substance is something that persists through change. Without this schema, no particular could be recognized as an instance of the category of substance. The categories are thus the transcendental universals that make objective experience possible: neither Platonic Forms nor mere names nor abstract ideas, but the a priori forms of the understanding.

Kant's account of categories as transcendental universals represents the most sophisticated response to the empiricist tradition. But his solution raises a new difficulty: if the categories are conditions the mind imposes on experience, they tell us nothing about things as they are in themselves. Hegel will argue that this restriction is unstable — that a logic of pure concepts, properly developed, is also a logic of reality itself.

Mill closes the debate on universals with a characteristically empiricist synthesis. Against Plato, he denies that universals are separately existing entities. Against Hobbes, he denies that all general classifications are equally arbitrary. Against Kant, he denies that any universal concepts are a priori. Universals are real uniformities in nature discovered by induction.

The key distinction is between real kinds and arbitrary collections. "Gold" names a real kind: things that share gold's observable properties also share many other properties, and investigation continually reveals more of them. "Things thought of on a Tuesday" does not name a real kind: knowing that something was thought of on Tuesday tells you nothing else about it. Real kinds carve nature at its joints; arbitrary collections do not.

Induction discovers real kinds by finding which collections of properties naturally hang together. The uniformity of nature (that things of the same kind behave similarly) is not an a priori truth but itself an inductive generalization, supported by the whole course of human experience. Universal propositions are thus not guaranteed by any prior necessity but are claims about actual regularities in nature, always open to revision.

Mill's position is the classical empiricist answer to the problem of universals: universals are real in the sense that nature has genuine structural regularities, but they are not independently existing entities: they exist only as the patterns that particular things jointly instantiate. This is the view that most working scientists implicitly adopt, and it remains the dominant position in naturalistic philosophy.