Personal identity

7. The biological approach

Despite the predominance of psychological continuity theories there have always been some philosophers who have defended the view that it is biological rather than psychological continuity that actually constitutes personal identity. Earlier versions of this approach tended to argue that personal identity consists in sameness of body. For a variety of reasons, including the difficulty of providing a precise definition of what a body is and of what makes for sameness of body, more recent instances tend to place identity in biological rather than bodily continuity. This means that instead of saying that identity depends upon the continuity of a physical body, these views hold that it consists in the continuity of a single organism. In its new, updated form the biological approach to personal identity, also called ‘animalism’, has presented a significant challenge to the dominance of psychological accounts.

A particularly well worked out defence of this view is found in the work of Eric Olson (1997). Olson’s argument for animalism takes place against the background of an assumed essentialism. According to this assumption, each concrete particular belongs most fundamentally to one and only one kind. This kind defines the individual’s essential properties in the sense that the individual cannot cease to belong to that kind without ceasing to be. A puppy, for instance, may cease to be a puppy simply by maturing into an adult dog; it may cease to be white-haired by growing a new, darker coat; but it cannot cease to be a dog without ceasing to exist. Olson calls the terms that name essential kinds substance concepts. Substance concepts (like dog) are contrasted with phase sortals, concepts that apply to a particular substance during some or all of its existence, but which it could exist without instantiating (concepts like puppy or white-haired creature.)

The difference between the psychological and biological approaches turns on whether we take person as our substance concept or as a phase sortal. Psychological theorists, who see our persistence conditions as determined by our personhood, take the former position, animalists the latter. The distinction between these two views can be easily seen by considering someone who falls into a permanent vegetative state. On the Lockean conception of what it means to be a person (which Olson takes on), when someone falls into a vegetative state they cease to be a person. If person is our substance concept, then we cannot continue as nonpersons; someone who falls into a vegetative state ceases to exist. If human is our substance concept, however, then someone who falls into a vegetative state continues to exist, but is no longer a person, just as a puppy who grows into an adult dog ceases to be a puppy without ceasing to exist.

Because each concrete particular can have one and only one substance concept, if person and human animal are both substance concepts, and we are essentially persons, then we cannot be essentially human animals. This raises awkward questions, Olson says, about the relation between persons and humans. If I am essentially a person, for instance, then I could not have been a foetus, since no foetus is a person as psychological theorists define the term. But if that is the case, then what happens when a foetus develops into a human person? Does it go out of existence to be replaced by a new entity? (He calls this the ‘foetus problem’.) If not, are there then two distinct but completely coincident entities, the person and the animal, that coexist? If so, how can it be that the person is thinking but the animal is not, given that the two coincide exactly? (He calls this the ‘thinking animal problem’.) And suppose this person falls into a vegetative state, does the person then cease to exist, leaving behind an animal that looks just like them but is really a distinct entity? Is this animal the same animal as the foetus that became the person? (He calls this the ‘vegetable problem’.) All of these difficult questions disappear, animalists say, if we simply hold that person is not a substance term but a phase sortal; then we can easily describe the above trajectory as one where a human animal starts out as a foetus, is a person for much of its life, and later ceases to be a person.

Olson’s arguments for animalism thus rest on the claim that human animal is a much more plausible candidate to be our substance concept than is person. He claims that the typical statement of the question of personal identity - ‘What makes a person at time t ₁ and a person at later time t ₂ the same person?’ - confuses matters by implying that in order for a person to survive they must survive as a person. But this is true only if person is our substance concept. If not, then a person need not continue to be a person to continue to exist any more than a puppy must continue to be a puppy to continue to exist. Olson thus suggests that we replace the question of what makes a person at one time identical to a person at a later time with the more neutral question of what makes a person at one time identical to anything at a later time.

Olson is also anxious, however, to explain (or explain away) the appeal of the psychological approach, since this view has been so widely accepted. This appeal, he argues, comes from a conflation of metaphysics and ethics. As we have seen, the arguments for psychological views depend upon the strong intuition that practical judgements track psychological rather than biological continuity. He is willing to concede these intuitions, but points out that a further step is needed to turn them into an account of personal identity, namely the assumption that these practical judgements must also be connected with identity. Psychological theorists give no independent argument for this assumption and it is, Olson says, controversial. Perhaps in ordinary circumstances we are only rightly held responsible for our own actions or can only appropriately feel egoistic concern for our own futures, but in the strange circumstances where psychological and biological continuity diverge this may no longer be true. If we do not presuppose a connection between metaphysical and practical facts about identity, the fact that our practical judgements track psychological continuity when it diverges from biological continuity might just as well be taken to show that these judgements can come apart from identity as that identity can come apart from biological continuity, and the intuitions behind the psychological approach can be accommodated by animalism.