What is the relationship between identity and unity? The two notions are often run together, but they are not the same. Identity concerns sameness, while unity concerns togetherness. Identity asks whether this is the same as that. Unity asks whether these features, moments, or parts belong to one whole. The difference is not trivial. One is concerned with identity when claiming that this chicken is the one that produces the most eggs. One is concerned with unity when pointing out that the chicken’s feathers form part of the unity of the chicken, while the nest in which she lays her eggs does not. The nest may stand in important relations to the chicken, but it does not belong to the chicken as constitutive of what the chicken is. An individual, then, is not merely something identifiable; it is a unity that can be distinguished from other unities by the properties it instantiates.
This distinction matters because a great deal of metaphysical confusion arises when identity is treated as though it could do the work of unity, or when unity is treated as though it were merely a disguised form of identity. Neither reduction succeeds. To say that something is identical with itself is not yet to say what makes it one. And to say that various features belong to one whole is not yet to say how that whole may be identified as the same across differing conditions of appearance or differing acts of reference. The two notions are thus internally related but not reducible to one another: unity concerns the ontological togetherness of a thing, while identity concerns the sameness of that one thing across differing acts of manifestation, description, or reference.
In logic, identity is treated as an equivalence relation. An equivalence relation holds over a domain just in case reflexivity, symmetry, and transitivity obtain. Thus if identity is symbolized by “=”, then for every element a in a domain, a = a; if a = b, then b = a; and if a = b and b = c, then a = c. At this level, identity is formal. It concerns the basic structure of sameness within a domain of discourse. Such formal treatment is indispensable, but it tells us very little by itself. It tells us how identity behaves, but not yet what identity amounts to in the world.
For that reason it is useful to distinguish between trivial self-identity and informative identity. That a = a is formally necessary and utterly unremarkable. It is not the kind of statement by which one learns anything substantive about the world. But a = b is often quite different. Frege’s famous example remains instructive. “The Morning Star is the Evening Star” is informative in a way that “The Morning Star is the Morning Star” is not. The former can extend knowledge. The latter cannot. Both are identity statements, yet only one seems to disclose something.
Why? Clearly not because “Morning Star” and “Evening Star” are the same expression. They are not. Nor is the point merely that they are two arbitrary labels later discovered to designate the same object. Frege’s great insight was that identity statements of this sort are informative because the same object may be given under different modes of presentation. The Morning Star and the Evening Star are not two different entities that happen to collapse into one. They are one and the same object, Venus, presented under different conditions of appearance and recognized under different descriptive routes. Identity here therefore concerns the sameness of what is referred to across a difference in how it is given.
This means that informative identity already presupposes more than logic alone can furnish. It presupposes phenomenological difference. We do not generate informative identity statements merely because we possess two names. We generate them because the object is encountered under different phenomenal or epistemic conditions. “Morning Star” and “Evening Star” are not simply linguistically different. They emerge from different appearances, different orientations, different conditions of observation. To learn that the Morning Star is the Evening Star is not merely to learn a fact about language. It is to learn that what appeared under distinct conditions is nonetheless one and the same being.
At this point Panayot Butchvarov’s distinction between objects and entities becomes helpful. Objects are what are given within experience, within the manifold of appearing. Entities are what ultimately are. One need not accept every feature of that distinction to grasp its usefulness here. The object Morning Star and the object Evening Star are differently given. Yet the entity referred to in each case is one. Identity judgments of the informative sort thus move from difference in givenness toward sameness in being. That is why they are significant. They do not merely register synonymy. They disclose ontological sameness across phenomenological difference.
But identity is still not unity. Even if one grants that a single entity may be given under multiple modes of presentation, one has not yet said what it is for that entity to be one. The problem of unity is distinct. Unity concerns the internal togetherness of a whole. Which features belong to the whole as constitutive of it, and which do not? Which moments are internal to the being of the thing, and which are merely externally related? This is not yet a question of whether one referring expression picks out the same item as another. It is a question of the ontological constitution of the thing itself.
The distinction can be put simply. Identity answers the question of sameness across reference or appearance. Unity answers the question of belonging within a whole. The chicken may be identified as the same chicken across different descriptions, times, and relations. But the unity of the chicken concerns something else entirely: that its feathers, bones, organs, and life-processes belong together as one living being, while the nest, the barn, and the farmer do not, however closely related they may be. The chicken and the nest may enter into a wide range of real relations, but they do not thereby form one individual substance.
This means that unity cannot be reduced to aggregation. A heap has plurality, but not genuine unity. A list has members, but not an internal principle of togetherness. A thing possesses unity when its features belong together as moments, aspects, or parts of one being. This is why unity is always a deeper metaphysical notion than mere collection. If identity concerns sameness, unity concerns the ontological “one” in virtue of which a thing is not merely many. The two notions are therefore linked but distinct. One may identify a heap, but that does not make it a unified individual. One may recognize a unity, but that does not yet settle every question of its identity across changing conditions of manifestation.
To put the point differently, identity without unity is thin. Unity without identity is mute. Identity without unity yields only the formal possibility that something is the same as itself or the same as that which is differently named. It does not yet tell us what kind of whole the thing is. Unity without identity may give us a togetherness of parts or moments, but without criteria of sameness it cannot explain how that one persists, is recognized, or is referred to across differing conditions. An ontology of the individual therefore requires both.
This brings us to individuation. What is an individual? It is not merely an instance of a universal, though it may instantiate universals. Nor is it merely a bundle of properties, though it has properties. Nor, I would argue, is it merely a formally self-identical item standing beneath predicates. An individual is a unity capable of identity across multiple acts of reference, description, and manifestation. That is to say, it is a concrete one whose togetherness is not reducible to its conceptual description, but which can nonetheless be identified as the same through differing modes of givenness.
This point is crucial. If one begins only with identity, one is tempted to think of the individual as that which remains the same under redescriptions. But that picture risks making the individual too thin. It becomes little more than a point of reference for varying predicates. If one begins only with unity, one is tempted to think of the individual as a whole without asking how that whole is encountered, intended, and recognized across different situations. But that too is inadequate. The individual must be both one and identifiable, both unified and selfsame across differing manifestations.
The problem becomes even more pressing when one asks what grounds this unity. It will not do merely to say that certain parts belong together. That is true, but insufficient. One wants to know what kind of belonging is at issue. Some relations are external. The nest is externally related to the chicken. Other relations are internal. The organs of the chicken belong to the chicken in a way the nest does not. Unity therefore concerns more than spatial proximity or causal interaction. It concerns ontological constitution. The features that belong to the unity of a thing are not simply attached to it from without; they are bound up with what the thing is.
This is one reason why I have become increasingly dissatisfied with any account that preserves individuality only as a bare point beneath qualities. Such views often understand identity well enough, in the sense that they secure numerical distinctness. But they do less well with unity. They can tell us that this is this one and not that one. They are less able to tell us what makes this one a concrete whole rather than a mere peg beneath predicates. Identity is secured, but unity remains underdescribed.
The more adequate path, it seems to me, is to say that an individual is a non-substitutable locus of unity capable of manifestation under differing conditions. That formulation tries to preserve both sides. The individual is non-substitutable: it is this one and not another. But it is also a locus of unity: its features belong together in a way that makes it a whole rather than a mere aggregate. And it is capable of manifestation under differing conditions: it may be referred to, described, and encountered through multiple modes of presentation without ceasing to be the same one.
Here one can see why identity statements of the Fregean kind matter. They remind us that sameness does not eliminate difference in givenness. The same thing may appear differently. But one can also now see why unity is deeper than identity alone. Unless there is already some ontological togetherness to the thing, there would be nothing there to be identified across those differences. Identity presupposes unity, even though unity is not reducible to identity. One identifies as the same only that which is already somehow one.
That point, I think, has broader implications. It bears on metaphysics, because it reminds us that sameness and wholeness are distinct categories. It bears on phenomenology, because it shows that identity judgments are rooted in differing conditions of givenness. It bears on ontology, because it presses us to ask what sort of being a whole must have in order to sustain identity across manifestation. And it bears on theology, because any serious account of personhood, hypostasis, incarnation, or sacramental presence will have to negotiate precisely these distinctions: sameness without collapse, unity without aggregation, manifestation without reduction.
The central claim may now be stated plainly. Identity concerns the sameness of what is referred to across difference in manifestation or description. Unity concerns the belonging-together of what constitutes one concrete whole. The individual requires both. It must be a unity in itself, and it must be capable of identity across acts of reference and conditions of appearance. Any account that ignores either side will remain incomplete.
Thus the ontology of the individual cannot begin with formal identity alone, nor with mere aggregation, nor with an unexamined appeal to “the same thing.” It must ask how a being can be one, how it can be given under differing conditions, and how it can remain itself throughout. Only then do we begin to approach the deeper metaphysical question: not merely whether something is the same, but what kind of one it must be in order to be the same at all.
That is where the real work begins.