An interactive thought experiment on identity, change, and what makes you you
Theseus's Ship — drag the slider to replace planks over time
Original wood
New wood
Locke argued that personal identity consists in the continuity of consciousness — memory linking past and present selves into one person. But what happens when memory fails, or when every physical part is replaced?
— After John Locke, An Essay Concerning Human Understanding (1689), Book II, Ch. 27
Question 1: The Classic Puzzle
At 100% replacement, is this still Theseus's ship?
All three answers have serious philosophical defenders! Option 3 is where most contemporary philosophers land — this is a case of conceptual underdetermination. Our concept of "same ship" wasn't built to handle this case. Locke would lean toward continuity; Hume would say there's no deep fact of the matter beyond our conventions.
Question 2: The Twist — The Rebuilt Ship
Suppose someone collected every original plank and reassembled them into a ship. Now there are TWO ships. Which one is really Theseus's?
This is the "branching problem" — a classic in personal identity theory. Derek Parfit used similar puzzles to argue that identity is not what matters. What matters is psychological connectedness, not some metaphysical fact about identity. (See Parfit, Reasons and Persons, 1984, Part III.)
Question 3: Apply It to Yourself
Your body replaces most of its cells over several years. Meanwhile, your beliefs, memories, and personality change throughout life. Given this, what makes you the same person you were at age 5?
These map to real theories! Option 1 = Locke's psychological theory. Option 2 = biological/animalist view (Olson, 1997). Option 3 = narrative identity (Ricoeur, Oneself as Another, 1992 — also covered in Module 4!). Option 4 = Hume's bundle theory and Parfit's reductionism. None is obviously correct — that's what makes this such a rich philosophical problem.
✍ Reflect & Connect
Think of a significant way you've changed over your life. Does the Ship of Theseus puzzle help you think about whether you're still the "same person"? Which theory of identity resonates most with your experience, and why?