Philosophy › Reason, experience & Enlightenment › British empiricism
What makes you the same person over time?
classic statement Locke, 1694; puzzle as old as the Ship of Theseus· Big question· Reality, mind & God
Mostly agreedGood evidence; some details uncertain.
The puzzle of what makes you at 70 the same person as the child you were at 7, despite changes in body and mind.
See it on the Philosophy map →The idea
Main answers. Body: you are the same living organism. Soul: an unchanging soul carries identity. Psychological continuity: Locke (1694) said you are whoever's past you can remember from the inside. No fixed self: Hume and the Buddha saw only a changing bundle of experiences. Test cases: the Ship of Theseus (replace every plank), amnesia, brain transplants, teleporters. Thomas Reid's 1785 objection to Locke: an old general remembers being a young officer, who remembered being a flogged boy, but the general does not.
Why it matters
It bears on responsibility (can you be punished for what you have forgotten?), on dementia care, and on what it would mean to survive death or be uploaded.
Think of it like
Like a building gut-renovated over decades: same address and name, but how much must survive for it to be the same building?
Where it comes from
Locke added the chapter 'Of Identity and Diversity' to his Essay in 1694; Plutarch records the Ship of Theseus, and Reid, Butler and Parfit carried the debate on.
Still debated
There is no consensus; Parfit argued identity may not be what matters, and teleporter and brain-splitting cases still divide philosophers.
Connections (2)
▸John Locke gave the memory-based answer to What makes you the same person over time?Well documented
The connection
Locke argued that a person is a thinking being that can consider itself the same across time, and that personal identity reaches as far back as consciousness, in effect memory, reaches. His case: if a prince's consciousness entered a cobbler's body, the person would be the prince.
When and how
The chapter 'Of Identity and Diversity' (Essay, Book 2, Chapter 27), added to the second edition in 1694 at William Molyneux's urging.
How we know
The chapter is the standard starting point; Joseph Butler (1736) and Thomas Reid (1785) published influential objections to it.
Debates and open questions
Whether Locke meant memory alone or a broader continuity of consciousness, and how his view handles forgetting, remains debated.
▸What makes you the same person over time? was radically reframed by Derek Parfit, Reasons and PersonsWell documented
The connection
Parfit argued that personal identity is not what matters. Using cases like a teleporter that destroys you and builds an exact copy on Mars, or a brain split between two bodies, he concluded that what we should care about is psychological connection, which comes in degrees. He found this freeing: less fear of death, more concern for others.
When and how
Reasons and Persons, Part 3, published in 1984 while Parfit was a fellow of All Souls College, Oxford.
How we know
Reasons and Persons is widely ranked among the most important 20th-century works of philosophy, and its cases are standard in courses on the self.
Debates and open questions
Critics argue identity does matter, for responsibility and survival, and question whether Parfit's view supports impartial ethics as he claimed.