Personal identity and survival

What it is

You share almost no atoms with the child in your earliest photograph. Your beliefs have changed, your body has changed, most of your memories of that period are gone or reconstructed. In what sense is that the same person as you?

The candidate answers are few and each has a standing objection:

• Bodily continuity — you are the same organism. Simple, but it makes identity survive the total destruction of memory and personality, which many find implausible
• Psychological continuity — you are linked to that child by an overlapping chain of memories, intentions and character. Intuitive, and it breaks in the cases below
• A soul — an unchanging bearer of identity underneath the changes. Solves it by definition, at the cost of positing something nobody can point to
• Nothing at all — the question is malformed and there is no fact to find

This is not idle. Everything on this site that claims something survives death is making a claim about personal identity, usually without noticing that the concept is in trouble before death is even mentioned.

Where it came from

Locke put the modern question in play in 1689 with the memory criterion: a person is the same person as far back as their consciousness extends. He was explicit that this is distinct from being the same body or the same soul.

The objections arrived fast and have never been answered cleanly. Joseph Butler pointed out the circularity — you cannot define personal identity by memory, because a genuine memory is already one where the rememberer is the person who had the experience. Thomas Reid pressed the transitivity problem with his brave officer: an old general remembers being a young officer, who remembered being a boy flogged for robbing an orchard, but the general does not remember the boy. By Locke's criterion the general is the officer, the officer is the boy, and the general is not the boy — which identity cannot tolerate.

The modern treatment is Derek Parfit's Reasons and Persons (1984), and its method is thought experiment pushed until something breaks. Teletransportation: a machine scans and destroys you here, reconstitutes you exactly there. Did you travel or did you die and a copy continue? Then fission: your brain hemispheres are separated and each is transplanted, both survive with your memories and character. They cannot both be you — identity does not branch — yet nothing was lost that would not be lost in an ordinary survival.

Parfit's conclusion was radical and he meant it literally. Identity is not what matters. What matters is psychological continuity and connectedness, which come in degrees, can branch, and do not require a further fact about whether some entity persists. There is no deep further fact. He reported finding this liberating rather than distressing — the walls of the glass tunnel he had been living in, he wrote, disappeared.

How it is used

Every survival claim presupposes an answer, and the traditions give incompatible ones. Bodily resurrection preserves the organism. An immortal soul preserves a substance. Buddhist rebirth explicitly denies a persisting self and holds that a causal continuum carries on without anyone travelling along it — a position startlingly close to Parfit's, as Parfit himself noticed and acknowledged.

Reincarnation research, mediumship and near-death accounts all rely on the assumption that there is a determinate person whose survival is at issue. If Parfit is right, the question "did I survive?" may not have a determinate answer even in ordinary cases.

What we can and cannot say

We can say no criterion has survived the thought experiments. This is one of the better worked-over problems in philosophy and it has resisted solution for three centuries.

We can say the psychological continuity view is the most widely held and that Parfit's reductionism is influential without being consensus. Critics — Richard Swinburne among them — argue the thought experiments prove less than claimed, and that our inability to say what happens in fission reflects a limit on our imagination rather than an absence of fact.

We can say the convergence between Parfit and Buddhist anattā is real and was arrived at independently, by argument rather than by contemplation. That is interesting. It is not proof of anything, and Parfit did not treat it as such.

What we cannot say is that survival claims are straightforwardly coherent or straightforwardly incoherent. Anyone asserting that something of them will persist is asserting something about identity that philosophy has not been able to underwrite — which is not a refutation, but it does mean the hard part of the claim is usually the part left unexamined.

Further reading

• John Locke, An Essay Concerning Human Understanding, Book II ch. 27 — where it starts.
• Derek Parfit, Reasons and Persons (1984), Part III — demanding, and among the most genuinely unsettling philosophy written in the last century.
• Eric Olson, The Human Animal (1997) — the case for bodily continuity, well argued against the tide.