John Locke, answered from the texts and cited to the page.
Identity must be relativized to the kind of thing whose identity is in question. The identity of a man (a living organism of the human species) is constituted by the continuity of life in the organized body.1 The identity of a person (a thinking intelligent being capable of considering itself as itself, the same thinking thing in different times and places) is constituted by sameness of consciousness — the same self-awareness extending backward through memory and forward through anticipation.23
Person is a forensic term: it concerns accountability, reward, and punishment, and its conditions of identity are those that ground the practices of holding accountable. The prince-and-cobbler thought experiment makes the structural claim plain: if the consciousness of the prince inhabits the body of the cobbler, the person is the prince (accountable for the prince's actions) and the man is the cobbler (the human organism that walks the streets).4 The man / person distinction is what most opponents have missed.5
This also shews wherein the Identity of the same Man consists; viz. in nothing but a participation of the same continued Life, 35 5. ldentity of A11imal1. 6. Ide11tity of Man. (14) [ut) the) 4-5 / the same 2-3 (15) and... Plant,) add. 4-5 (16) they exist] 4er-5 (likewire Coste) 1 they exist, 4 1 it exists, one Body, 2-3 (29) in an Animal) add.An Essay Concerning Human Understanding, p. 355
Had I the same consciousness, 16. Conscioumm maires the rame Perron. (5), the... Resurrection] 4-5 1 at the Resurrection the same Person 2-3 (6) which] add. 4-5 (17-18) he... besides) 4-5 1 it would to every one be the same Cobler beside 2-3 (24) [zndJSpirit] 2er-5 1 Spirits 2 (29) -ever] 11. Re gis ter (31) Actions,] 4-5 1 Actions 2-3 (1. btfou, 35) makesJ 2-31 maire 4-5 Chap.An Essay Concerning Human Understanding, p. 364
In this persona/ Identity is founded ail the Right and Justice of Reward and Punishment; Happiness and Misery, being that, for 17. Self depends on Conscioumm. 18-20. Object of Rt111ard and Pu11ishment. (1) [z11dJ that) add. 3-5 (12) self-consciousness] Coste adds a marginal /inguistic note.An Essay Concerning Human Understanding, pp. 364–365
So that this consciousness not reaching to any of the Actions of either of those Men, he is no more one self with either of them, than if the Soul or immaterial Spirit, that now informs him, had been 30 created, and began to exist, when it began to inform his present Body, though it were never so true, that the same Spirit that informed Nestor's or Thersites's Body, were numerically the same that now informs his.An Essay Concerning Human Understanding, pp. 362–363
The Prince, 'tis plain, who vouches this Story, and our Author who relates it from him, both of them call this Talker a Parrot; and I ask any one else who thinks such a Story fit to be told, whether if this Parrot, and all of its kind, had always talked as we have a Princes word for it, this one did, Chap.An Essay Concerning Human Understanding, p. 358
One of the founding chapters of modern philosophy of mind. Butler's response (1736) charges that consciousness presupposes the identity it is supposed to constitute and therefore cannot constitute it. Reid's brave-officer case (1785) charges that memory-based identity violates transitivity. Parfit's Reasons and Persons (1984) is the contemporary inheritance: psychological continuity and connectedness as the descendant criterion. Stillingfleet's seventeenth-century version of the substance objection (the resurrection of the same person requires sameness of substance, which the consciousness criterion does not deliver) ran through the Three Replies of 1697-1699.