Identity of Selves
It is plausibly urged that there can be no identity without identity conditions (“criteria”): for example, material objects are identical in virtue of being spatiotemporally coincident, or sets are identical if and only if they share their members. Likewise, we could say that distinctness requires conditions (“criteria”) of distinctness: no two things can be distinct without this distinctness consisting in something, such as difference of spatial location or diversity of set membership. Distinct things must be distinguished by something, in virtue of something, as a consequence of something; they can’t be just barely distinct, primitively so, inexplicably so. This principle meets with no ready counterexample: material objects are distinguished by their location, sets by their members, events by their causes and effects, numbers by their position in an arithmetical series, hairstyles by their shape, and so on. But what about selves—what distinguishes them from each other? What does the (alleged) fact of distinctness consist in here? We normally think we are distinct selves from other people (as we say), but what kind of fact is that: can it be seen and heard, can it be detected, can it be conceived? It is easy to appreciate that it can’t be spatial location, because selves don’t have (definite) spatial location (save derivatively on bodies); and if they did it need not coincide with the location of the body or brain (there could be several selves in one body or brain and a single self spread across several bodies). It is not even clear that selves could not all occupy a single location. Nor do selves have the identity and distinctness conditions of sets or numbers or hairstyles. They need their own sui generis identity and distinctness conditions. We can’t say they are distinguished by overall mental state (including character and personality), because distinct selves can have identical overall mental state and because mental state changes over time (and across possible worlds). Intuitively, the self (ego, subject, soul, “I”) is a transcendent entity not reducible to any other category of thing with its distinctive identity and distinctness conditions. It is a kind of vanishing point, a pure locus of awareness, an indefinable something, not even in the world. This entity is not distinguished from others of its kind by anything perceptible, or even thinkable. It is thus a prime candidate for the null identity condition: selves are distinct from each other just in virtue of being selves—primitively, inexplicably. They may indeed be the only entities in reality with this property—the bare-distinctness property. My self differs from your self just in virtue of being a distinct self; nothing further can be said. That would certainly be surprising and anomalous, but (it may be claimed) it just has to be accepted: when I look at another person I must say to myself, “That self is not identical to this self (me), but I have no idea what makes them non-identical”.
But there is an alternative to this unsatisfactory conclusion, namely that selves are not distinct. We don’t even know what it would be for selves to be distinct. We talk this way, but we don’t know what it means. Rather, what it is to be a self is to be the only self, as a matter of conceptual necessity: for there is no coherent concept of self non-identity. We know what bodily non-identity is, or brain non-identity, or overall mental state non-identity: but we don’t know what it is for selves to be non-identical. There is simply no fact that could constitute such distinctness. No fact that we can produce adds up to the alleged fact of self-distinctness. The only proper conclusion then is that there are no such facts, and hence no such thing as a plurality of selves. Compare God: suppose someone maintains that God could have a twin or a very similar God-like brother. Theological scruples aside the problem with this suggestion is that there is nothing for such a distinction between gods to consist in, since God does not exist in time and space (or is arranged in a certain position in a series of gods). Any being like God would have to be God, because the grounds of possible distinctness don’t exist where God exists. Nor has anyone ever supposed otherwise (the Greek gods existed here on earth): God isn’t a spatial being so his distinctness from other gods couldn’t consist in a difference of spatial location. It is the same with the self: spatial separation can’t be the ground of self-distinctness (this is most obvious when we consider dualism). The difference is that we can perceive the bodies of human selves but we can’t perceive God’s body (he doesn’t have one), so we easily slide into self-pluralism for human selves but not for the divine self. But human selves don’t admit of plurality either since they have no conditions of identity and distinctness. It is impossible for selves to be distinct—there can be no such fact. The single human (and animal) self has many different states of which particular creatures may be conscious, but these states have but one subject, which participates in the life of each creature. Believers in metempsychosis think that a single self can exist in different animal bodies over time, so that each animal shares a single self; the same thing could be held about the selves (sic) that exist simultaneously in human and animal bodies—there is just one despite an appearance of multiplicity. The various animal forms mask the identity of the reincarnated subject for believers in metempsychosis; according to self-monism, the diversity of bodies masks the underlying identity of conscious subject. And this means the necessary identity of conscious subjects, since selves constitutionally have no identity and distinctness conditions—they must therefore be all one. Appearances must be illusory; or else there are no such actual appearances, just a metaphysical prejudice. If you ask the man or woman in the street whether he or she is identical self-wise with other people, you are not likely to get a firm reply. True, people distinguish themselves from each other according to material-object and individual-organism criteria, but do they consciously think that their innermost self is ontologically distinct from other such selves? Maybe they could quickly be brought round to the self-monism doctrine (apparently it is widespread in the East). After all, the principle that difference requires differentiation has the look of self-evidence; and no one thinks it’s easy to say what a self is, or where one begins and ends. At any rate, it would be too strong to say that a belief in a plurality of selves arises simply from the operation of the senses like other illusions: it really doesn’t look to me as if I am not the same self as you (contrast the lines in the Muller-Lyer illusion). Perhaps we can be said to have discovered by philosophical argument that all selves are one and the same, but this may just be a piece of knowledge added to a previous agnosticism or simple lack of interest, not a revision of what the senses tell us about the self. Admittedly, according to self-monism it is true that we marry ourselves, love and hate ourselves, compete with ourselves, help ourselves out, or harm ourselves; but we need not regard ourselves as otherwise identical, because the same self can have a different body, personality, and lifespan. Your spouse may indeed share your self but not your body and your body’s history—these are distinct from yours. The self is a pretty rarified and obscure thing, so it won’t matter much practically whether other people share yours or not—though the felt gulf between oneself and others (human and animal) may well strike us as less wide and sharp under the new dispensation. We make errors of identity all the time (as Frege reminded us): this one is just more metaphysical than most, and therefore less practically important. Depending on temperament, it may gladden the heart or wound one’s pride (the prince is the same self as the pauper, the judge and criminal likewise). I myself welcome a deeper kinship with animal selves, while finding my identity with other human selves mildly disagreeable, but that’s just me. What is most startling perhaps is that this state of affairs could not be otherwise: it is built into the nature of selves that there can only be one of them, simply because there is nothing (no fact) for the distinctness of selves to consist in. I really don’t know what it would be to be someone other than me.
 I put it this way to remind the reader of the Kripke-Wittgenstein discussion of meaning. Kripke asks what fact could constitute meaning and comes up with nothing; similarly we can ask what fact constitutes the distinctness of selves and we come up with nothing. Therefore, it may seem, meaning doesn’t exist and selves don’t either; but we can save meaning and the self by adopting a radical revision in how we think of them, as will become apparent. We avoid a “skeptical paradox” by rethinking our habitual conception of the things in question. In both cases, we give up the picture of the isolated particular.
 This would be like adopting an irreducibility view of meaning in the face of the Kripke-Wittgenstein challenge: it is just a brute fact that one self is numerically distinct from another, as it is a brute fact that “+” means addition. That kind of response may have some plausibility for meaning, but for the self is runs hard up against the principle that there can be no distinctness without distinctness conditions (which holds for even the simplest kinds of entity such as elementary particles). Not for nothing has the self been deemed peerlessly problematic. We don’t even know how to count them! It’s a lot simpler to think there is just the one.
 The closest analogy I can find is universals: what makes one universal distinct from another? Not spatial location obviously, and not position in a series, or membership, or shape: but we can say that universals differ when they admit of different instantiations—or else they would indeed collapse into each other. The self seems unique in its lack of differentiating conditions. Solipsism turns out to be true, but not in the way it was originally intended. (Another option, of course, is that selves don’t exist at all.)