Personal identity

What makes someone at one time the same person as someone at another - and whether that is what actually matters.

Theme: Mind, self and consciousness
Tradition: Western
Term fixed: 1694

In plain terms

The child in your earliest photograph shares almost nothing physical with you. The atoms are gone, the beliefs are gone, most of the memories are gone. Yet that is you, and saying so is not a figure of speech - it carries debts, promises, criminal liability and inheritance.

So something makes the two the same person. Locke's answer was memory: you are whoever you can remember being. The obvious problem is that memory fades, so an old officer who remembers the young soldier, who remembers the boy, may not remember the boy at all - and identity is supposed to be transitive.

Repairs are available. But the deeper worry is different: perhaps the question has no answer in the hard cases because it was never a question about a fact, only about how we have decided to treat people.

As a philosopher would put it

Locke grounds identity in continuity of consciousness, deliberately detaching person from both body and soul; Reid's objection is the transitivity problem, and later psychological-continuity theories answer it with overlapping chains of connection rather than direct memory.

The rival is the biological view: a person is an organism, and identity is the continuity of a life. It handles the awkward cases - foetuses, the deeply demented - that psychological views strain on, at the cost of implying that a successful brain transplant would move a body rather than a person.

Parfit's argument is that the question is less important than it looks. In fission cases identity cannot hold with both successors, yet nothing has been lost that anyone should mind about; what matters is psychological continuity and connectedness, which come in degrees and can hold one-many. If that is right, our concern for our own future is not concern for the identity of a thing but for relations that admit of more and less.

Where you meet it

An advance directive lets a competent person set out what treatment they refuse if they later lose capacity, and it binds. In England, under the Mental Capacity Act 2005, a valid advance decision refusing life-sustaining treatment must be followed.

The philosophical difficulty was set out by Ronald Dworkin using the case he called Margo: a woman with advanced Alzheimer's who is, by every account, contented - she enjoys her days and has no distress. Years earlier, competent and appalled by the prospect, she signed a directive refusing antibiotics for a treatable infection.

The earlier person's settled values conflict with the later person's present interests, and a clinician has to act. Dworkin argued that critical interests formed across a life outrank experiential ones; Rebecca Dresser argued that this hands power over a happy person to someone who no longer exists in the relevant sense. Statute has chosen a side. Neither the philosophy nor the medical ethics has settled.

What is actually disputed

Whether personal identity is a further fact.

On one view there is a determinate answer in every case, even one we could not discover. On Parfit's view identity is not a deep further fact beyond physical and psychological continuities, and once those are described there is nothing left to know; where identity is indeterminate, the question is empty rather than hard.

The practical stakes are unusual for a metaphysical dispute. Advance directives, criminal responsibility for offences committed decades earlier, prudential concern for one's own old age and the ethics of severe dementia all turn on it, and none of them can wait. That is why the biological and psychological camps persist: each handles a set of real cases the other handles badly, and no institution can adopt neither.

Commonly confused with

identity in the social sense Who someone takes themselves to be can change completely without any question arising about whether they are the same person.
Self 1694 The self is the question of whether there is a subject at all. This is the question of what makes a subject at one time the same as one at another.
legal personhood A legal person can be a company. The law's criteria are practical decisions, and they are what the philosophy is trying to assess.

Defined against

Anātman If there is no persisting subject, the question of what makes it the same subject does not arise in the form Locke posed it

Philosophers

John Locke Continuity of consciousness rather than substance
Thomas Reid The transitivity objection, in the officer example
David Hume No self to be identical with - only a bundle and a habit

Works

An Essay Concerning Human Understanding The chapter that created the topic
An Inquiry into the Human Mind Reid's objections
A Treatise of Human Nature The bundle account
Reasons and Persons Fission, and the claim that identity is not what matters

Schools

British Empiricism Where the psychological account is developed
Scottish Common Sense School Where it is attacked
Early Theravada Buddhism Where continuity without identity is the orthodox position
Classical Utilitarianism Where Parfit's conclusions bear directly on how to weigh future people

Related concepts

Identity 1714 · Self 1694 · Anātman c. 450 BC · Responsibility c. 340 BC · Change c. 500 BC

Locke added the chapter in the 1694 second edition, separating person from man and from substance; every subsequent account is a response to it.