8.2 John Locke on Personal Identity

What this lecture covers

This lecture asks what makes a person at one time the same person as someone at an earlier time. It sits within a run of lectures on personal identity and builds on the discussion of identity for matter and living organisms before turning to Locke's specific account of persons.

After watching, you should be able to state Locke's criterion of identity for matter, bodies and organisms, explain why he separates the concept of a person from that of a human organism, and describe why he grounds personal identity in consciousness rather than an immaterial soul.

Key ideas

• Identity criteria vary by kind: Locke holds that what makes something the same over time depends on what kind of thing it is (particle, mass of matter, organism, or person).
• Particles: a particle stays the same as long as there is a continuous trajectory connecting it over time.
• Masses of matter: a lump of clay stays the same lump only if it keeps exactly the same particles, however they are arranged.
• Sorites-style problem: applying the strict "same particles" rule to matter runs into a Paradox of the Heap / Paradox of the Bald Man style problem once you ask whether losing a single particle changes identity.
• Organisms: a living thing's identity is constituted by a continuous organized life, not by keeping the same matter, since organisms constantly exchange matter through eating and excreting.
• Person versus human: Locke distinguishes the human organism (a biological continuity) from the person (a thinking, reflective being aware of itself over time).
• Forensic perspective: for Locke, personal identity matters practically because it underlies concern for one's future and questions of reward, punishment and an afterlife.
• Consciousness over soul: Locke rejects grounding personal identity in an immaterial soul, since we have no access to such substance and cannot even be sure it persists unchanged.

Before you watch

• Review the earlier lecture(s) in this personal identity sequence, since this one assumes familiarity with the general problem of identity over time.
• Bring some prior sense of the mind-body distinction, as Locke's move away from the soul depends on it.

Check your understanding

1. Why does Locke think the criterion for sameness of a lump of matter cannot be applied unchanged to living organisms?
2. How does the Paradox of the Bald Man illustrate a difficulty in Locke's account of identity for masses of matter?
3. What distinction does Locke draw between a "human" and a "person"?
4. Why does Locke consider appeal to an immaterial soul unsatisfactory as a basis for personal identity?
5. What point does the brain-swap thought experiment bring out about what we care about in personal identity?