Persons and Minds in the Inventory
You are reading this. Something is doing so. What kind of entity is it?
The question is not the one usually asked under "personal identity" — what makes the person now the same as the child then — though the two are connected. It is the prior, ontological question: which item in the inventory is the person, and does the inventory need a category for minds.
The section treats both briefly and deliberately. Personal identity has its home in the persistence discussion, while the present subject, minimal and narrative self, and no-self views are treated in What Is the Self?; what belongs here is the categorial question.
Candidates
An animal. Animalism (Olson, van Inwagen): you are a human organism, and your persistence conditions are biological. Its principal argument is the thinking animal problem: there is certainly a human animal sitting where you are, and that animal has a working brain, so it thinks. If you are not the animal, there are two thinkers here, and you cannot know which one you are. The cleanest way out is to identify them.
A psychological continuer. The Lockean tradition: you are constituted by continuity of memory, personality, and intention, and you would go with your psychology if it were transferred. This matches our practical concern — what we care about in survival seems psychological — at the cost of the thinking-animal problem and of a person who is not identical with any biological thing.
A brain, or a part of one. A compromise that keeps the physical basis while allowing the animal to survive without you.
A bundle. Hume: introspection finds perceptions, never a self that has them, so the self is a bundle of experiences. Inherits every difficulty of bundle theory plus the special one that the bundling relation must be memory or causal connectedness, which presupposes the self it constructs.
A soul. A simple immaterial substance. Answers the identity question decisively — you go where the soul goes — and pays for it with the interaction problem and with the difficulty that a simple substance has no explanation of why it is associated with this body.
A four-dimensional worm. You are an extended spacetime object with temporal parts, and "the person now" refers to a stage. Dissolves several puzzles and requires the whole perdurantist metaphysic.
Fission
The case that drives the literature. Split a brain and transplant the hemispheres into two bodies, each with your memories and character. Both are equally good candidates to be you. But they are two, and you are one, so by Leibniz's Law you cannot be both. Actual commissurotomy and the separate question of how many current subjects it produces are treated in Split Brains and Counting Subjects.
The options exhaust the possible shapes: you are one of them (arbitrary, since nothing distinguishes them); you are neither, so fission is death (odd, since double survival would be worse than single); you were always two coincident people (Lewis's multiple-occupancy view, requiring temporal parts); or identity is not what matters, and the important relation is psychological continuity, which can hold one-many.
Parfit's conclusion — that identity is not what matters in survival — is the most influential, and its ontological upshot is deflationary: personal identity is not a deep further fact over and above physical and psychological continuities. If that is right, the question "which candidate is the person?" may have no determinate answer, and the dispute above is less substantive than it looks.
Is the mental a category?
The second question. Grant that persons are animals; are mental properties an addition to the inventory?
Substance dualism makes minds a separate category of thing. Property dualism keeps one kind of substance and adds a category of properties not identical with, and not grounded in, physical ones. Physicalism denies both, holding that mental facts are grounded in physical facts. The views and their different explanatory costs are compared in Positions on Mind and Body.
The exclusion argument is the standing difficulty for property dualism and for non-reductive physicalism alike. If every physical effect has a sufficient physical cause, and mental properties are distinct from physical ones, then mental causes are either redundant or systematically overdetermining. Stated in the section's vocabulary: can a derivative entity or property do causal work that its ground does not already do? The full argument and its principal replies are developed in The Problem of Mental Causation.
That question was answered affirmatively for physics on the fundamentality page. Quasiparticles are uncontroversially derivative and indispensably explanatory; a phonon's grounding in lattice vibrations does not make phonon-explanations redundant. Whether the same move works for the mental is disputed — the physics case involves no distinct cause, only a coarse-grained description of the same one, which is precisely what non-reductive physicalism wants to say and property dualism cannot.
Why the ontology matters elsewhere
The categorial question is not idle. Moral responsibility attaches to agents, and what kind of thing an agent is constrains what agency can be: the libertarian appeal to agent causation requires that a substance be an irreducible cause, which is unavailable if persons are bundles or four-dimensional worms, and which the event ontology of Davidson has no room for. The connection is developed from the other side in the discussion of moral responsibility.
Where persons sit
This is the category question applied to ourselves, and it is the one case where the answer is not obviously independent of us — since whatever we conclude, we are the things concluding it.
Its distinctive feature is that the candidate answers are already positions taken elsewhere in the section. Animalism is a substance ontology; the bundle view is bundle theory; the worm view is perdurantism; Parfit's deflationism about the further fact has the same shape as deflationism about existence questions generally. The person is not a special case so much as a place where every general commitment shows its consequences at once.