The idea
The Ship of Theseus is one of philosophy's oldest puzzles about identity. The Athenians preserved Theseus's ship and, over the years, replaced every plank as it rotted. The question: after all the planks have been replaced, is it still the same ship?
This puzzle generalises. It applies to your body (your cells replace themselves over time), to nations, to companies, to anything that persists through change. The question is: what makes a thing the same thing over time?
The main positions
Continuity of structure
The ship remains the same because its structural pattern and function persist. Individual parts are just matter serving the pattern.
If someone collected all the original planks and reassembled the original ship, which one would be the real Ship of Theseus? Two ships, one pattern.
Continuity of matter
Identity follows the original material. The ship with all new planks is a different ship; the reassembled original would be the real one.
Our bodies replace most of their atoms every few years. On this view, you are not the same person you were as a child — which most people find implausible.
No fact of the matter
Identity is a convention we impose on the world for practical purposes, not an objective fact. The question has no deep answer — only practical ones.
This seems to dissolve rather than solve the puzzle. Legal and personal identity decisions require real answers, not philosophical retreat.
Key thinkers
- Plutarch
- Posed the puzzle in Life of Theseus (c. 75 CE). The problem has been discussed ever since.
- Thomas Hobbes
- Added a version where someone collects the old planks and reassembles the ship, sharpening the paradox.
- Derek Parfit
- Reasons and Persons (1984) applied identity puzzles to persons and argued that identity is not what matters — continuity of psychology is.