Same and Other

Plato numbers sameness and otherness among the five greatest kinds in the Sophist, setting them beside being, motion, and rest. The occasion for doing so is the problem of false speech. If each Form simply is what it is, and nothing further can be said of it, then to say of anything that it is not becomes impossible, and the sophist who trades in falsehood cannot be convicted of error. Plato's proposal is that otherness runs through the whole of reality, each Form being the same as itself and other than all the rest. What is called non-being, on this account, need not be absolute nothingness; it may be understood as otherness, the not-being-this of whatever is something else. The discussion of same and other thus begins in company with the problems treated under the ideas of Being and of One and Many.

The Timaeus assigns the same pair a cosmological office. In fashioning the World Soul, the Demiurge blends three ingredients, Being, Same, and Other, and from the mixture forms two revolutions. The circle of the Same governs the motion of the fixed stars; the circle of the Other governs the wandering of the planets. Cognition is held to follow the same division. When the soul's circle of the Same turns undisturbed, the result is rational knowledge; when the circle of the Other prevails, the result is opinion and sensation. On this view identity and difference are not relations that the mind imposes in comparing one thing with another, but principles built into the constitution of the world and of the soul that knows it. Whether the pair should be conceived cosmologically in this manner, or confined to the analysis of predication, remains in dispute among those who come after.

Elsewhere Plato does not let the doctrine stand unexamined. In the Parmenides, the young Socrates is asked how two individual men can be alike in being men without a separate idea of Man, and, if such an idea is required, whether a further idea is not then needed to account for the likeness between each man and the idea itself. The regress is stated in the dialogue and not resolved there. A difficulty from the opposite quarter appears in the doctrine of universal flux that Plato ascribes to Heraclitus, which permits nothing to remain the same for an instant and so, if admitted, would nullify all further discussion of sameness. How many things can share one nature is a question that belongs also to the idea of Universal and Particular, where the several positions taken about universals afford different answers to it.

What later writers take from Plato is less the list of greatest kinds than the proposal that non-being be construed as otherness. Aristotle accepts the logical point while declining the cosmological account, and holds that sameness must be distinguished into its several senses rather than treated as one world-governing kind. Plotinus, on the other hand, retains the kinds and places them within a hierarchy of procession, so that otherness measures the distance of each derived reality from its source.

Aristotle receives the Platonic kinds and applies to them his usual method of distinction. Where Plato had spoken of the Same and the Other as single Forms, Aristotle holds that "same" is said in several ways. Two things may be the same in number, as Cicero and Tully; the same in species, as two men; the same in genus, as a man and a horse, both being animals. Sameness in general he treats as a kind of unity, calling it a unity of the being either of more than one thing or of one thing when it is treated as more than one, so that to the one belong the same and the like and the equal, while to plurality belong the other and the unlike and the unequal. Each grade of sameness carries its own consequences in argument, and to pass from one grade to another without notice is to fall into fallacy.

Difference is divided with equal care. In Metaphysics X, otherness is separated both from difference and from contrariety. Whatever is not identical with something else is other than it, and need not be other in any definite respect; but what is different is different from a particular thing in a particular respect, so that, as Aristotle puts it, there must be something identical by which two things differ. Contraries are opposed within a single genus, admit of intermediates and of degrees, and enter into the account of change, whereas bare otherness does none of this work. The differentia, in turn, is the difference by which a genus is divided into its species, as rational divides animal. A man and an ass differ in this way, and are called similar because their specific difference is accompanied by generic sameness.

Two further theses bear on the question of how far sameness extends. Aristotle denies that there is any single all-embracing genus. There are rather several supreme genera, substance, quantity, quality and the rest, and the variety of species within them is finite; between the contrary species of one genus he allows no intermediates, so that the order of species resembles the order of the whole numbers rather than a continuous series. Yet things diverse in genus are not on that account incomparable, for they may be one by analogy, each standing to something else in the same relation, as the hand is a tool of tools and the mind the form of forms. "Being" likewise is said of everything in every category, though not in the same sense of a substance and of a quantity. What such predication implies about heterogeneous things is pursued further under the ideas of Relation and of Universal and Particular.

By multiplying the senses of sameness and difference, Aristotle converts a pair of Forms into an apparatus for classification, definition, and demonstration, and the practice of defining by genus and differentia rests upon it. What he leaves unsettled is why the several senses should go under one name, and whether their unity is merely verbal. Aquinas takes up that question in asking how a term can be predicated of God and of creatures alike, and converts Aristotle's remark that things one by analogy are not all one in genus into a general doctrine of analogical predication.

Plotinus takes over the five greatest kinds and sets them within a graded cosmos. He holds it necessary, in addition to Being, Motion, and Rest, to posit Identity and Difference, so that there are five genera in all. The One itself stands beyond all distinction, and beyond sameness as well, since to call it the same as itself would already introduce duality into what is simple. Otherness enters with procession: the One overflows its perfection, and whatever comes from it is necessarily other than its source. Intellect is the first such otherness, the level at which being and thought are distinguished as a subject that thinks and an object thought. Whether anything can be predicated of a principle so conceived is a question Plotinus does not evade, and he grants that the names given to the One are given by way of indication rather than description.

Within Intellect the Forms subsist as a multiplicity that remains one. Each is identical with itself and distinct from all the rest, and this internal differentiation is what keeps Intellect from being an undivided blank. Soul, proceeding further, introduces greater otherness still: succession in time, extension in place, the dispersal of one life among many bodies. Matter lies at the far limit, where determination and selfhood are nearly absent. On this scheme the likeness of two individual men is explained by a third and separate reality in which both share, and of such an archetype Plotinus says that it is present in multiplicity as one seal is present in many impressions. Whether a separate archetype accounts for likeness, or falls to the regress that Parmenides raises against it in Plato's dialogue, is treated under the idea of Universal and Particular.

Otherness, for Plotinus, is nowhere a clean severance. Every derived reality continues to depend upon its source and preserves its identity by epistrophe, the turning back toward the higher principle from which it came. A soul that forgets its origin and takes itself to be its body has to that extent lost its proper sameness, and the philosophical ascent is described as the recovery of that identity. Difference that does not return is dissolution. The doctrine thus gives the pair of same and other a moral bearing as well as a metaphysical one, since the ordering of a life is measured by the degree to which it holds to its source rather than scattering into multiplicity.

Later writers divide over how much of this structure can be kept. Augustine retains the pattern of procession and return while locating it in a personal God whose unity is not reached by the withdrawal of every predicate. Aquinas, working in the same tradition, accounts for the likeness between infinite and finite being by a doctrine of analogy rather than by a separate archetype, holding that creatures resemble God as what is by participation resembles what is essentially. The difficulty Plotinus poses, how anything can proceed from a source without being simply other than it, continues to shape the treatment of Being and of One and Many.

Aquinas addresses a question that neither Aristotle nor Plotinus had occasion to raise, namely how three persons may be really distinct from one another and yet absolutely one in substance. A metaphysics of identity framed for creatures tends here to one of two failures: either the persons collapse into one, as the Sabellians held, or they are divided into three gods. Aquinas proposes instead a doctrine of subsistent relations. Father, Son, and Holy Spirit are distinguished by relations of origin alone, which are paternity, filiation, and spiration. These relations are not accidents inhering in a subject, as relations among creatures are; they are the divine essence itself, and they stand in real opposition to one another. Real distinction is accordingly grounded in relational opposition rather than in any division of substance.

The point on which the argument turns is that in God relation and essence do not differ in reality but only in our manner of conceiving them. The essence is neither divided nor multiplied, and there is one act of being, one intellect, one will. The persons are not parts of God, nor modes under which God appears, but the essence subsisting in opposed relations. Real distinction, in the sense that no person is another, is thus held together with numerical identity of substance, in the sense that each person is the one God. No Aristotelian category accommodates this without strain, and Aquinas acknowledges the strain; the logic of relation is carried beyond what Aristotle had asked of it.

Outside theology, Aquinas treats the general notions of same and other in a manner that bears on the same difficulties. The relation signified by the term "the same," he holds, is a logical relation only when taken in regard to absolutely the same thing, since a thing's order to itself is observed by reason rather than found among things; the case is otherwise when things are called the same generically or specifically. Difference, in his account, presupposes composition, for we seek difference where we also find resemblance, and simple things are diverse through themselves and do not differ from one another by any components. Where things fall under no common genus and are yet alike in some way, their likeness is analogical. Being is common to all things only according to some sort of analogy, and the likeness of creatures to God is of this kind, God being essential being and other things beings by participation. The threefold distinction of univocal, equivocal, and analogical names is treated further under the idea of Sign and Symbol.

What Aquinas contributes to the discussion is the claim that identity and distinction need not attach to substances alone, and that relational opposition can ground a real difference where no division of substance is admitted. His doctrine of analogy converts Aristotle's remark that things one by analogy are not all one in genus into the broader proposition that things not one in genus, yet alike in some way, are one by analogy. Leibniz approaches the individuation of substances from the opposite direction, asking not how distinction can survive identity of essence but whether numerical difference is possible at all without difference of properties.

Locke begins the question of identity with the conditions under which it can be raised at all. To ask whether anything is the same is always to refer it to something that existed at a determinate time and place, since one thing cannot have two beginnings of existence, nor two things one beginning. An atom, being at a given instant what it is and nothing else, remains the same so long as its existence continues, and a mass of atoms is the same mass so long as no atom is added or taken away. With living things the rule fails, for an oak grown from a plant to a great tree is still the same oak, and a colt grown up to a horse is all the while the same horse, though in neither case is the mass of matter the same. Identity in organisms, Locke concludes, lies in the participation of one continued life by particles constantly succeeding one another in the same organized body.

In the case of man a further problem arises, that of personal identity. Locke separates the identity of the man, which follows the rule for organisms, from the identity of the person, which he places in the continuity of consciousness. Whatever has the consciousness of present and past actions is the same person to whom those actions belong. If the soul of a prince, carrying the prince's memories, were to inform the body of a cobbler, the resulting being would be the same person as the prince though the same man as the cobbler. To illustrate what continues an animal the same, Locke turns to the comparison of a watch, whose identity lies in an organization of parts to an end rather than in the matter organized, and asks that the machine be imagined as one continued body whose parts are repaired and replaced under one common life.

Locke's interest in the question is in large part practical. On personal identity, he says, is founded all the right and justice of reward and punishment. Persons are held answerable for past actions because they are conscious of having performed them, and to punish Socrates waking for what Socrates sleeping did, when the waking man was never conscious of it, would be no more right than to punish one twin for what his brother did. The difficulty is that memory is fallible and that consciousness is interrupted by sleep and by forgetting. Locke answers that consciousness rather than perfect recall is the criterion, and that cases beyond human discernment will be settled at the last judgment. Whether the answer suffices has been much disputed, but the form of the question, what makes the same person rather than the same substance, has largely governed later treatments.

Locke's separation of the person from the substance made personal identity a subject in its own right. Leibniz answers in the New Essays that consciousness is too narrow a mark, since a substance may persist through states of which it retains no awareness. Hume declines the appeal to divine justice and presses the argument further, asking whether introspection discloses any continuing self at all. William James, later still, accepts identity by continuity of consciousness but takes the continuity itself to require explanation, and finds it in the resemblance and the continuity of the parts of the stream of thought. What the persistence of the person implies for theories of an imperishable substance is treated under the idea of Soul.

Leibniz answers both Aristotle and Locke by way of a single principle, the identity of indiscernibles. If two things share every property, they are not two but one. There are no two leaves in a garden, and no two drops of water, perfectly alike in every respect. Numerical distinction without qualitative distinction he takes to be impossible, and impossible on other than empirical grounds. The principle follows for him from the principle of sufficient reason, since God would have no ground for placing one of two indistinguishable substances here and the other there. Understood as the self-sameness of what is one in number and in existence, identity is a notion most parties to the discussion concede; what is disputed is how much may be inferred from it concerning the individuation of things.

The principle bears against two positions at once, the scholastic doctrine that matter individuates form and the atomist picture of qualitatively identical particles differing only in place. Each monad, each simple substance, contains a complete individual concept by which it is marked off from every other, and its situation among the rest follows from its own internal states rather than standing as a brute external fact. Otherness is accordingly grounded always in intrinsic difference. To this Leibniz joins his account of identical propositions, in which the predicate is contained in the subject and which he takes to be the first principles of all reasoning, so that identity in the logical sense underlies demonstration as identity in the real sense underlies individuation.

Against Locke in particular, Leibniz argues in the New Essays that consciousness is too narrow a criterion of personal identity. A man may lack all awareness of past states and remain the same substance with the same complete concept, for what he is does not depend upon what he can recall. Locke, on this view, has taken a mark by which identity is recognized for the thing in which identity consists. Leibniz allows that consciousness has its importance for moral accountability, which is Locke's chief concern, but denies that the moral question settles the metaphysical one.

The identity of indiscernibles altered what an account of individuation was expected to supply. Numerical difference could no longer be left as a bare fact requiring no explanation; either an internal ground had to be produced for it, or the demand itself had to be refused. Kant refuses it, arguing that two drops of water may agree in every concept and still be two, since they occupy different positions in space, and that position belongs to the form of intuition rather than to the concept of a thing. Hegel accepts the principle while altering its ground, taking determinacy itself, rather than a divine reason for choosing, to require that a thing differ internally from others.

Hume carries Locke's separation of identity from substance to a further conclusion. Looking inward, he reports, we never come upon a self standing behind the perceptions; we find only the perceptions themselves, of heat and cold, light and shade, pleasure and pain, succeeding one another without interval. The mind is not a theater in which such scenes are performed for a spectator, since no spectator is met with apart from the scenes. Men, he says, are nothing but a bundle or collection of different perceptions, which succeed each other with an inconceivable rapidity and are in a perpetual flux and movement. The claim reaches beyond the denial of personal identity, for it affirms an utter diversity among perceptions, as if there were no manner of relation between them, each being for Hume a distinct existence. Those who hold that anything endures through change, as Aristotle holds of substances, stand opposed to him on this point.

The question then becomes why identity is nevertheless ascribed. Hume's answer is that the imagination supplies it, and that similarity is taken for sameness. Because successive perceptions resemble one another, and because memory traces a chain of causally connected experiences, the mind passes easily along the series and mistakes the ease of that passage for the observation of something continuing. The same account is given of the identity we ascribe to plants, to animal bodies, and to artifacts whose parts are gradually replaced. In each case the ascription is a fiction of the imagination, natural and hardly avoidable in practice, yet not to be defended by argument. Since we have no impression of a self, and since by Hume's rule every genuine idea derives from an impression, there is on his principles no idea of a self to be had.

Hume did not find the result comfortable. In the Appendix to the Treatise he confesses that the subject of personal identity leaves him in a labyrinth from which he cannot extricate himself. He can find no principle uniting successive perceptions into one self, and he can give no satisfactory account of the compulsion under which the mind supposes one. He states the difficulty and leaves it standing. Whether a doctrine of universal flux can be maintained without nullifying all further discussion of sameness is an older question, raised against Heraclitus and pressed further by Cratylus, who criticized Heraclitus for saying that one cannot step twice into the same river on the ground that one could not do it even once. Among things that lack identity, no comparison can be made.

Hume's argument obliged later writers to consider that identity might be supplied by the mind rather than found among things. Kant frames his account of the unity of apperception in direct response, granting that no self is met with in intuition while denying that the unity of consciousness can be dispensed with. William James returns to the same ground, agreeing that the sense of personal identity is a perception of sameness like any other, grounded in resemblance or in continuity before the mind, while declining Hume's conclusion that distinct perceptions bear no manner of relation to one another.

Kant agrees with Hume that no empirical intuition of a substantial self is to be had. Inner sense yields a succession of representations and never a bare "I" standing behind them. He denies, however, that Hume's conclusion follows. The unity of the self is not something discovered in experience but a condition of experience. The proposition "I think" must be capable of accompanying all my representations, since without this synthetic unity of apperception the manifold given in intuition could never be combined into one consciousness, and there would be no experience at all but only scattered impressions belonging to no one. Unity of consciousness, he writes, would be impossible if the mind could not become conscious of the identity of the function by which it unites the manifold; and the consciousness of the identity of one's self is at the same time a consciousness of the necessary unity of the synthesis of all appearances according to concepts.

Against Leibniz, Kant holds the identity of indiscernibles to rest upon a confusion. Leibniz treats place as following from the internal states of substances, whereas Kant argues that two drops of water may agree in every concept and still be two, because they stand in different positions in space. Spatial and temporal location are forms of intuition rather than predicates reducible to concepts, so that otherness may be grounded in the structure of sensibility alone. The principle holds of concepts, then, but not of objects given in intuition. On the further question whether all things belong at last to one genus, Kant affirms a principle of homogeneity, according to which the diverse genera are divisions of one supreme and general genus, together with correlative principles of specification and of continuity, by which every genus requires species and between any two species intermediate species always remain possible. Aristotle's doctrine of several supreme genera, and of a discontinuous order of species, stands opposed on both counts.

In the Paralogisms, Kant examines the inferences of rational psychology. From the "I think" the rationalists had concluded that the self is a substance, that it is simple, that it is numerically identical through time, and that it is distinct from objects in space. Each inference he treats as a paralogism, a fallacy in which a logical function is taken for a metaphysical fact. The "I think" is the form of all thinking, and from a form so understood nothing follows concerning the nature, the simplicity, or the persistence of any underlying thing. What is represented through it is a transcendental subject of thoughts, known only through the thoughts that are its predicates.

Kant's position lies between Hume's denial of the self and the rationalist claim to know it as a substance. The transcendental "I think" preserves the unity that experience requires without converting that unity into an object of knowledge. The distinction thus drawn between formal and substantial identity enters most later treatments of the self, and Hegel takes it up by asking whether an identity that merely excludes difference can be determinate at all. What the persistence of the self implies for the doctrine of an imperishable substance belongs rather to the idea of Soul.

Hegel declines to treat identity and difference as two concepts, each intelligible apart from the other. In the Science of Logic he argues that the ordinary law of identity, "A is A," taken as a statement about a thing considered by itself, is empty and tautological. Identity in the concrete sense includes difference within itself. To say what a thing is requires saying what it is not: light is intelligible against darkness, the finite in relation to the infinite. An identity that excludes all difference he calls abstract, and without content. On this view the relation between a thing and everything else is not something added after the thing has been determined, but enters into the determination itself.

The formula he offers is that identity is the identity of identity and non-identity. A determinate thing maintains itself, on this account, by holding together its positive character and its negative relation to what it is not. A plant is a plant in being neither stone nor animal nor concept, and these negations are not accidents befalling it from outside but belong to what the plant is. The Doctrine of Essence develops the sequence of identity, difference, opposition, and contradiction, and undertakes to show how each passes into the one that follows. Mere difference becomes determinate opposition when the terms are set against one another within a common ground; opposition becomes contradiction when the identity of each term is found to depend upon the very term it excludes.

Hegel also takes up Leibniz's identity of indiscernibles, accepting the principle while altering its ground. The reason no two things are exactly alike is not, he holds, that God would lack a sufficient reason for creating duplicates, but that determinacy itself requires internal differentiation. To be something determinate is already to differ from other things, and that difference enters into the constitution of the thing. Identity without internal articulation would be indeterminacy, which is to say nothing at all. The same consideration governs his objection to the abstract self-identity that Kant's formal "I think" appeared to him to leave standing, since a subject that is no more than the form of thinking has as yet no content by which it might be distinguished from anything.

After Hegel the law of identity is not easily restored as a simple first principle, and the question becomes how far sameness and otherness penetrate one another. His logic of essence is the most sustained attempt in the tradition to treat identity and difference as one self-developing structure. Those who hold, with Aristotle and Aquinas, that a thing's identity is prior to its relations, and those who follow Hegel in taking relation to enter into identity itself, continue to divide over questions treated under the ideas of Relation, of Opposition, and of One and Many.