The Ship of Theseus is a thought experiment about identity and change. Theseus was a Greek hero. His ship was preserved in Athens. Over time, the wooden planks rotted and were replaced. Eventually, every plank was new. Was it still the Ship of Theseus? If not, when did it stop being the ship? If the old planks were reassembled, which ship is the real one?

The puzzle goes back to Plutarch. It raises questions about identity. What makes something the same over time? Is it the material? Is it the form? Is it the history? A person changes over time. Cells are replaced. Memories fade. Are you the same person you were ten years ago? The Ship of Theseus suggests that identity is not simple.

Ship of Theseus questions

• Is identity about material continuity?
• Is identity about form and structure?
• Is identity about history and continuity?
• Can identity survive complete replacement?
• What if the old parts are reassembled?

The thought experiment has no single answer. It depends on your theory of identity. If identity is material, the ship stops being the Ship of Theseus when the last original plank is replaced. If identity is formal, the ship remains the same as long as the structure is the same. If identity is historical, the ship remains the same as long as the history is continuous. The puzzle applies to persons, organizations, and nations. A company changes its employees and products. Is it still the same company? A nation changes its borders and constitution. Is it still the same nation? The Ship of Theseus is a puzzle about persistence. It asks: what makes something the same across time? The answer is not obvious. The puzzle remains.