Universal and Particular

The problem of the universal, as the historians of philosophy beginning with Aristotle recount it, enters the tradition through Plato's theory of Forms. When Socrates asks what virtue is, he is not content with a list of particular virtues; he seeks the one thing common to them all. Plato's answer is that this common nature is an actually existing object, an Idea or Form, in which the many particular instances participate; it is neither a word covering many cases nor only a concept in the mind. The same demand for the one in the many appears under the ideas of Same and Other and of One and Many, and under Definition it appears as the Socratic insistence that a genuine definition state the formulable essence of a kind rather than enumerate its members.

The Forms are eternal, unchanging, and accessible only to reason. Particular beautiful things are beautiful, on this view, because they participate in Beauty Itself; yet they are always becoming and always mingled with what is not beauty, so that only the Form is beautiful without qualification. In the Republic the ascending line from imagination through belief and reasoning to pure intellect traces the path from the changing many to the unchanging one. In the Timaeus the maker of the world is said to fashion sensible particulars after eternal patterns. How participation is to be understood (whether as resemblance, as sharing a whole, or as sharing a part) remains, in the dialogues themselves, a difficulty rather than a finished doctrine.

That difficulty is pressed hard in the Parmenides. If the Form is wholly present in each of many particulars, it cannot remain one and indivisible; if each particular has only a part of it, the Form is no longer the simple essence it was taken to be. A further objection, later called the third-man regress, asks whether the likeness between particular men and the Form of Man does not require yet another Form to account for that likeness, and so on without end. Plato states these objections without, in the dialogue, resolving them to everyone's satisfaction. Aristotle will treat the separation of Forms from particulars as the decisive error; later writers will ask whether any such separate entities are needed at all for definition, classification, or science.

What later ages call extreme realism (the view that universals exist separately and are more real than particulars) takes its classic statement from Plato. Aristotle will deny that separate Forms explain anything and will locate the universal in particular things and in the abstractive act of the intellect. Aquinas will try to preserve the insight by placing the exemplars in the divine mind rather than among self-subsistent Ideas. The nominalists will ask whether the machinery of Forms is needed once names and concepts are carefully distinguished from the individuals they signify.

Aristotle's criticism of the theory of separately existing Forms is, on his own account, the point at which he is most sharply opposed to Plato. To say that the Forms are patterns and that other things share in them is, he argues, to use empty words and poetical metaphors. Positing eternal duplicates of sensible things multiplies entities without explaining why the many are of one nature. If participation means resemblance, a further term is needed to account for the likeness between particular and Form, and the regress that appears in Plato's own Parmenides returns. Related objections, under the ideas of Form and of Being, concern whether anything universal can be a substance, and whether science, which is of the universal, can have for its object only what exists in individuals.

Aristotle's alternative is that only individual substances exist, whether sensible or intelligible, perishable or eternal, and that no universal can exist separately in and of itself. He does not thereby deny the reality of the universal. Without the universal, he holds, scientific knowledge as distinct from mere sense-perception is impossible. The form that constitutes human nature is individual in Socrates and in Callias; it becomes actually universal when the mind, by abstraction, separates that form from the individual matter of these men and receives it as the concept "man." The universal thus exists potentially in particular things and actually in the abstract concepts of the intellect. Later writers call this position moderate realism, in contrast both to the extreme realism of separate Ideas and to the view that universals have no extra-mental being at all.

The difficulty that remains is how science can be of the universal if only individuals really exist. Aristotle's answer is that the universal term "man," if truly predicated of an indefinite number of individuals, must signify something common to them; yet that common nature is not actually universal as it exists in each, since whatever exists in the individual is itself individual. The mind's abstractive power makes the potential universal actual as an object of thought. Questions about the object of definition and about the common names of everyday speech, treated more fully under Definition and under Sign and Symbol, turn on the same distinction between what is common in things and what is universal only as conceived.

Aristotle's moderate realism becomes the standard position of the later Scholastic tradition. Aquinas will develop it by adding that the forms of things exist also as exemplars in the divine mind. The difficulty Aristotle leaves, how one form can be wholly present in indefinitely many particulars without being divided among them, is seized upon by William of Ockham and others who argue that only individuals are real and that the universal is only in the soul.

Aquinas presents his account of universals in the course of stating what he takes to be the issue between Plato and Aristotle, and of amending both in light of Christian teaching. Plato, he says, supposed that the forms of natural things subsist apart from matter and are therefore actually intelligible, so that corporeal matter is formed by participating in them. Aristotle denied that the forms of natural things exist apart from matter, and since forms in matter are not actually intelligible, the natures we understand must be made actually intelligible by the intellect's abstractive act. Aquinas adds a third consideration drawn from Augustine: the exemplars of all creatures exist in the divine mind, according to which things are formed and the soul knows them. The result is a threefold distinction: forms are in the human mind by abstraction from sensible particulars; they are in individual things; and prior to their existence in things they are in God as divine ideas.

These three modes are not three rival theories of the same object but three ways of considering form. God knows the nature of man as an eternal archetype, though Aquinas insists that in God himself there is no distinction between universal and particular in the mode of created knowledge. Each human being is man by virtue of the form existing in him under conditions of particularity. The human intellect grasps man as a universal by abstracting that form from its individual conditions of matter, time, and place. In the order of generation the potential universal in things precedes the actual universal in the mind; the intention of universality, the relation of one and the same to many, is due to intellectual abstraction and is subsequent in our knowledge. Questions about divine knowledge and about the status of ideas in the mind of God are taken up more fully under the ideas of God, Idea, and Form.

The process of abstraction is central. The intellect illuminates the phantasm, the sensory image retained in memory, by stripping away individual material features and grasping what is essential and common. The result is the intelligible species, which is neither this man nor a free-floating humanity, but the form of humanity as received under conditions of universality and immateriality. Aquinas holds that Plato erred in concluding, from the fact that the form is in the intellect under those conditions, that the things themselves must subsist under the same conditions. The form of the thing known need not be in the knower in the same manner as in the thing known.

Aquinas's threefold account is the full Scholastic development of moderate realism. When Ockham argues that nothing common really exists outside the soul in an individual substance, and that universals are only terms predicable of many, the synthesis is contested from within the same tradition. Hobbes, Locke, Berkeley, and Hume inherit lines of thought that lean toward nominalism or conceptualism; other later writers retain, in altered form, a place for real common natures or for a priori universal concepts.

Hobbes takes the nominalist position in a thorough form. Of names, some are proper and singular to one thing only, and some are common to many things. A universal name such as "man" or "stone" is imposed on many things for their similitude in some quality or other accident. The things named are every one of them individual and singular; there is nothing in the world universal but names. Universality, on this view, is a property of words alone, which shows itself in the meaning of general or common names. The question how common names get their significance, treated also under Sign and Symbol and under Definition, is for Hobbes answered entirely within the theory of language and of the marks men use for memory and communication.

This doctrine has a polemical bearing on the Scholastic dispute over whether universals exist before things, in things, or after things. Abstract entities such as "human nature" or "the essence of man," when treated as discoveries about the world rather than as products of naming, are, for Hobbes, verbal creations. The controversy that occupied the schools is, on his account, largely a dispute about words. He does not deny resemblance among individuals; he denies that resemblance requires a universal entity over and above the individuals and the name by which they are jointly called. Classification and definition remain possible, but they rest on the conventions of speech and on the similitudes men notice, not on separately existing common natures.

The consequences for science are considerable. If universals are only names, then definitions are conventions, and the knowledge produced by demonstration is knowledge of the implications of our own definitions rather than of the nature of things independent of language. Reasoning becomes reckoning with names. Whether such a view can account for the necessity claimed by mathematics and natural philosophy is a question later writers press. Leibniz and Kant, among others, will argue that the universal concepts employed in science cannot be merely nominal if science is to yield more than arbitrary connections among signs.

Hobbes sets much of the agenda for the modern empiricist treatment of universals. Locke will refine the account by distinguishing nominal from real essence and by placing abstract general ideas between the name and the particular. Berkeley will deny abstract general ideas while retaining general names. Hume will reduce the work of the universal to custom and the association of similar particulars. Against this line of thought, Kant's doctrine of the categories will attempt a new grounding for universal and necessary concepts.

Locke occupies a middle position often called conceptualism. He agrees with the nominalist that general and universal belong not to the real existence of things but are inventions and creatures of the understanding. He differs from a pure nominalism of the Hobbesian sort in holding that general terms are signs of general ideas, and that ideas become general by a process of abstraction. The mind takes a particular idea received from particular objects and separates from it the circumstances of time, place, and other concomitant ideas that determine it to this or that particular existence. By that separation the idea is made capable of representing more individuals than one, each of which has a conformity to the abstract idea and is said to be of that sort. The same issues appear under Experience and under Sign and Symbol, where the origin of general meanings in particular perception is again in question.

This process of abstraction is, for Locke, a genuine activity of the understanding, not the mere assignment of names. Yet the abstract general idea is not a Platonic Form existing outside the mind, nor is it the real essence of the kind as that essence exists in things. Locke does not deny that things have real essences; he denies that our universal notions give us knowledge of those real essences. Abstract ideas, he writes, give us no knowledge of existence at all. Universal propositions of whose truth we can have certain knowledge concern not existence but the agreement or disagreement of our abstract ideas. In this respect he leans toward moderate realism less than Aquinas and more than Ockham, while remaining within an empiricist account of how general ideas are formed.

The account generates a difficulty that Locke himself notes. The general idea of triangle must be neither equilateral, isosceles, nor scalene, but all and none of these at once; in effect it is something imperfect that cannot exist. Locke means, it seems, that there can be no counterpart in reality to our general ideas. Berkeley will take the same "imperfection" as proof that such abstract ideas cannot exist even in the mind. The further question, how the many individuals represented by one abstract idea have in them a conformity to that idea, returns the old riddle of common nature in a psychological form: if only particulars exist, what in them justifies the application of one abstract idea to many?

Locke's theory of abstract general ideas becomes the immediate target of Berkeley's critique and the starting point of Hume's revision. The claim that general terms require something in the mind to back them, even if not separately existing universals, is widely retained among later empiricists, who differ mainly on whether that something is an abstract idea, a representative particular, or a habit of association.

Berkeley attacks Locke's doctrine of abstract general ideas as a source of confusion in philosophy. He denies that he can abstract from one another, or conceive separately, those qualities which it is impossible should exist so separated, or that he can frame a general notion by abstracting from particulars in the manner Locke describes. The abstract idea of triangle that is neither equilateral nor isosceles nor scalene, yet all three at once, is for him a psychological impossibility. One may name such a thing; one cannot form the corresponding idea. Abstract general ideas, so understood, are not genuine mental entities but verbal fictions that philosophers have mistaken for ideas and then been puzzled not to find in their minds. The critique belongs as much to the theory of mind and of language as to the traditional problem of universals.

Berkeley's alternative is that a word becomes general by being made the sign not of an abstract general idea but of several particular ideas, any one of which it indifferently suggests to the mind. An idea which, considered in itself, is particular becomes general by being made to represent or stand for all other particular ideas of the same sort. When a geometer proves something about triangles in general, he proves it of a particular triangle taken as representative of its class. Universality lies in the use of the idea and of the name, not in an abstract content stripped of all determination. A man may consider a figure merely as triangular without attending to the particular qualities of the angles or the relations of the sides; so far he may abstract, but that will never prove that he can frame an abstract general inconsistent idea of a triangle.

Whether this nominalism escapes the older riddle is itself disputed. What is there in one set of particular ideas, as opposed to another, that makes it possible for a general name to signify any one of them indifferently? If each particular idea were absolutely unique and had nothing in common with any other, the universal would seem to have no truth even at the level of names. Berkeley's appeal to similarity among ideas reintroduces a general relation, and the question how similarity is given without a universal concept is left for later writers. Under Same and Other the same difficulty appears as the problem of how two things can be alike without something common; under Induction it appears as the problem of projecting from observed cases to unobserved ones of the same kind.

Berkeley's critique is influential both because it is directed against Locke's version of abstraction and because it leads naturally to the question Hume will press further: if there are only particular ideas and names, what is the ultimate basis for the unity of a class and for the reliable application of a general term?

Hume agrees with Berkeley that there are no abstract general ideas: every idea is a particular. He goes beyond Berkeley in explaining how general terms work without treating even a representative particular idea as a stable bearer of abstract content. The key is custom. Through repeated experience of similar things, the mind forms a habit of associating a general name with any particular that falls in the relevant class. All general ideas, he holds, are nothing but particular ones annexed to a certain term, which gives them a more extensive signification and makes them recall upon occasion other individuals which are similar to them. It is the resemblance alone that gives rise to the general idea. The account belongs as much to the psychology of association as to the logic of universals, and it connects with the treatment of habit, experience, and induction elsewhere in the tradition.

When we hear the word "triangle," the mind revives some particular triangular idea, but the habit of association with other similar ideas is also activated. If the word were used in a way that excluded equilateral triangles, the resemblance of those triangles stored in memory would, on Hume's view, immediately mark the misuse. The "universal" is not an abstract idea but a habitual readiness to apply the term to any sufficiently similar particular. Generality is thus a skill sustained by association rather than the deployment of a pre-formed abstract content. Whether this psychologistic grounding can satisfy the logician who seeks formal properties of concepts, or the scientist who claims necessary connections among kinds, is a question Hume's successors raise.

The account still relies on resemblance, and resemblance is itself a relation among many. Kant will argue that to recognize two things as resembling each other is already to subsume them under a common concept, so that the most basic act of grouping particulars already presupposes universal forms of the understanding. James will later remark that nominalists are somehow forced to admit a quasi-universal, something thought as if it were universal though it is not, and that their talk of an indefinite number of particular ideas vacillates between the subjective and objective points of view. The old riddle thus returns: if only particulars exist, what in them or in the mind justifies the application of one name to many?

Hume's account of generality is a nominalism that still assigns a real role to resemblance. Kant will reply that resemblance is constituted by the understanding rather than simply given in experience, so that the categories are required even for the basic act of grouping particulars under a common concept. Mill will later seek real kinds in nature without restoring either Platonic Forms or a priori categories.

Kant argues that the empiricist account of generality fails at a critical point. If general terms rest only on habits of association formed by resemblance, the question remains how resemblance itself is recognized. To take two things as resembling each other is already, on Kant's view, to bring them under a common concept. The most basic act of grouping particulars therefore presupposes universal forms of thought; it cannot be the origin of those forms. 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 conditions under which experience of objects is possible. Substance, causality, community, reality, and negation are among the fundamental ways in which the mind organizes the manifold of intuition. Related issues are treated under Mind, Judgment, and Experience.

The schema of each category explains how a pure concept applies to sensible particulars. The schema of substance, for example, is permanence in time: a substance is something that persists through change. Without such schemata, no particular could be recognized as an instance of a category. The categories are thus neither Platonic Forms existing independently of mind and world, nor mere names, nor abstract ideas formed by stripping particulars of their differences. They are the a priori forms of the understanding by which the manifold is thought as objective. Universality and necessity, which empiricism had grounded in custom or denied, are restored as features of the conceptual structure of experience rather than as discoveries of separate essences independent of mind.

This solution, if accepted, limits what can be claimed about things as they are in themselves. The categories determine objects of possible experience; they do not yield knowledge of a reality wholly independent of the conditions of human cognition. Whether that restriction is stable, or whether a logic of pure concepts properly developed is also a logic of reality itself, is a question Hegel will press. Whether any universal concepts are a priori at all is a question Mill will deny from an empiricist standpoint. The problem of the universal bears on science, induction, and the status of necessary judgment; Kant's account relocates that problem inside the structure of the knowing mind.

Kant's doctrine of the categories is a principal modern alternative both to Platonic realism and to the several forms of empiricist nominalism and conceptualism. Hegel will develop a logic of the concrete universal in which individuality is the unity of universal and particular. Mill will return to the claim that general and universal are attributes of names and that real kinds, if they exist, are uniformities discovered by induction rather than a priori forms of the understanding.

Mill's treatment of universals is an empiricist synthesis that tries to avoid the extremes of the earlier debate. Against Plato, he denies that universals are separately existing entities. Against a pure Hobbesian nominalism, he denies that all general classifications are equally arbitrary. Against Kant, he denies that any universal concepts are a priori. General and universal, he holds, are attributes of names, not of things: there is nothing general or universal but names. Yet some of the classifications that names mark answer to real uniformities in nature, discovered by induction rather than imposed by the mind or guaranteed by eternal Forms. The connection of this view with Induction and with Science is direct: the logic of general propositions is the logic of how we learn from experience which groupings of things hang together.

The distinction between real kinds and arbitrary collections is central. "Gold" names a real kind: things that share gold's observable properties also share many other properties, and further investigation continually reveals more of them. A collection such as "things thought of on a Tuesday" does not name a real kind; knowing that something was thought of on Tuesday tells one nothing further about it. Things said to be of the same kind, Mill writes, are things that resemble each other in so many and such important features as to suggest and justify the belief that they will be found to resemble each other still further in other qualities. Real kinds, on this account, carve nature at joints that inquiry discloses; arbitrary collections do not. The question how two individuals can share a common nature without a separate universal returns here as a question about the structure of natural regularities rather than about Forms or abstract ideas.

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 for Mill an a priori truth but itself an inductive generalization, supported by the course of human experience and always open to revision. Universal propositions are claims about actual regularities in nature, not expressions of necessary relations among a priori concepts, and not reports of participation in eternal Ideas. Whether this view can account for the necessity claimed by mathematics, or for the categories Kant held to be conditions of experience, remains contested. Whether it adequately answers the older demand for a common nature in things, as distinct from a name and a pattern of resemblance, is likewise disputed.

Mill's position is a classical empiricist answer to the problem of universals: universals are real only as structural regularities that particular things jointly instantiate, not as independent entities. Later naturalistic philosophy often works with something like this view, while other traditions continue to press realist or transcendental alternatives. The conversation that began with Socrates' demand for the one in the many thus remains open under several guises: definition, classification, induction, and the status of scientific law.