Essay Concerning Human Understanding, by John Locke
In a radical philosophical innovation introduced in the second edition of his Essay Concerning Human Understanding (1694, book 2, chap. 27), Locke separated substance and personal identity, the “man” and the person.
The identity of the man, he wrote, consists in “a participation of the same continued life, in succession vitally united to the same organized body” (§6). The person, in contrast, is “a thinking being, that has reason and reflection, and can consider itself as itself, the same thinking thing, in different times and places” (§9). Thus, if the soul of a prince, containing the consciousness of the prince’s past life, is transferred into a cobbler’s soulless body, then the being who resembles the cobbler would in fact be the prince (§15). In Locke’s view, personal identity requires the capacity to recognize one’s actions and accept responsibility for them. In turn, this capacity implies a continuity of memory and consciousness, which the philosopher identified to “the sameness of a rational being.”
It follows that “as far as this consciousness can be extended backwards to any past action or thought, so far reaches the identity of that person” (§9). In other words, personal identity depends exclusively on the “same consciousness that makes a man be himself to himself,” regardless of the substances to which it might be “annexed” (§10). We just mentioned the cobbler and the prince, an example of Locke’s strategy of psychologizing personal identity with the help of thought experiments. Another such experiment concerns the little finger: If my consciousness is located in my little finger, and this finger is cut off my hand, then, Locke claimed, “it is evident the little finger would be the person, the same person; and self then would have nothing to do with the rest of the body” (§17). In short, bodies become things we have, not things we are; in turn, personal identity becomes purely psychological and distinct from bodily identity.