Personal Identity

What it asks

You share almost no matter with the child in your earliest photograph, remember little of that child's life, and hold few of its beliefs. You are nevertheless the same person. What does that consist in?

The question matters because a great deal follows from the answer. Punishment assumes the person punished is the one who acted. Promises assume the person bound is the one who gave the word. Prudence assumes that the person who will suffer tomorrow's hangover is you.

The recurring problems

Memory circularity. Locke made continuity of memory the criterion. Butler objected at once that remembering an experience as yours already assumes it was yours, so the account presupposes what it explains.

The brave officer. Reid's case: an old general remembers being a young officer, who remembered being a flogged schoolboy, but the general remembers nothing of the schoolboy. By the memory criterion he both is and is not that child.

Fission. Split a brain and transplant each half successfully. Two people, each psychologically continuous with the original. They cannot both be you, they are symmetrical, and it is absurd that a survivable operation on one half becomes fatal because the other half also survived.

Whether identity is what matters. Parfit's answer to fission was to accept it and conclude that identity is not the important relation - what matters is psychological continuity, which can hold to a degree and can hold with more than one person.

How it developed

Locke created the modern problem in 1694, in a chapter added to the second edition of the Essay. By separating the person from both the soul and the body and locating identity in consciousness, he made it possible for the question to be asked independently of theology, and it has been asked that way since.

Butler and Reid produced the standard objections within a generation, and both are still the first things taught.

Hume drew the sceptical conclusion: introspect as hard as you like and you find perceptions, never a self having them. The self is a bundle, held together by relations rather than by a thing.

The modern phase begins with the thought experiments - teletransportation, brain transplants, gradual replacement - and culminates in Parfit's Reasons and Persons in 1984, which argued that our concern for our own future survival is not supported by anything in the metaphysics, and that seeing this clearly is liberating rather than distressing.

The positions within it

Psychological continuity theories descend from Locke. Animalism holds that we are organisms, so identity is biological continuity and the psychology is beside the point. The simple view holds that personal identity is basic and cannot be analysed further. Bundle theories deny there is a self to be identical with. All are in the Schools section.

The Buddhist tradition reached the bundle position two thousand years earlier and worked out its consequences much further - see the entry on abhidharma.

Where it stands now

Animalism has grown at the expense of psychological accounts, largely on the strength of one question: if you are a set of psychological relations, what is the human animal sitting in your chair, and why is it not also thinking?

The practical end of the field has grown faster. Dementia, persistent vegetative states, advance directives and the moral status of the person a patient has become are all versions of this question with something at stake, and they have made it a working problem in medical ethics rather than a puzzle case.