It is a peculiarity of the question 'what makes me the same person across time?' that most who entertain it for the first time take the answer to be obvious, and most who entertain it for the second find the answer harder to formulate. The candidates that suggest themselves at first — the continuing body, the persistent memory, an underlying soul — each turn out, under modest pressure, to leak in places. The body is in continual material exchange with its surroundings; memory is patchy, reconstructive, and prone to import what it claims merely to retrieve; the soul, if invoked, is invoked precisely as that which cannot be specified, and so cannot answer the question to which it was offered as a reply.
The Lockean refinement located identity in the continuity of consciousness — broadly, in chains of memory that link present awareness to past awareness. The thought has obvious appeal: it accommodates change in body and personality while preserving a recognisable thread. Yet, as Reid and others objected, the chain is troubled by its own gaps. A general who, late in life, remembered his cadet self but had no recollection of an earlier officer he had once been is, on the strict Lockean account, identical with the cadet, identical with the officer, but the cadet is not identical with the officer — an arithmetical embarrassment for a relation that ought to be transitive.
Parfit's more recent move was to recommend giving up the demand that identity be all-or-nothing and to settle for psychological continuity in degrees. What matters in survival, on this view, is not whether the future being is strictly identical with the present one — a question that may admit no determinate answer in branching or duplicating cases — but how richly the future being is connected to the present one by memory, intention, character, and the like. The recommendation has the disconcerting consequence that some of the questions about which we care most — whether the person who wakes from the surgery will be me — may have no fact of the matter to answer them, only descriptions to give.
This is a place where philosophy and ordinary thought genuinely diverge. The ordinary thought wants a determinate self that either survives or does not; the analytic argument keeps producing reasons to doubt that the determinate self was ever there. The honest position is not to flatten the discrepancy in either direction. The persistent intuition deserves to be heard, for it bears on the practical structure of choice, planning, and concern; but the arguments that pressure it also deserve to be heard, for they have repeatedly survived the most patient attempts to defeat them. The most that can be said is that the question is older than philosophy and likely to outlast any of its current answers.
The primary purpose of the passage is to: