The origins of this thought experiment are not completely clear, but according to Marc Cohen (2004), it was first expressed in writing by Plutarch in the Vita Thesei.
There exists a ship owned by Theseus, who was a brave warrior. Theseus’ ship was decided to be kept and maintained by the Greeks as a memorial of his life. However, over time the parts of the ship would decay and would require replacement. After a long time, every single part of the original ship of Theseus had been replaced by new parts.
The question we need to answer is: Is this is ship still the ship of Theseus?
If you answer yes, why? If no, when did it cease to be Theseus’ ship?
After you consider your answer to the first thought experiment, consider this next thought experiment, which comes from Richard Swinburne (2010):
Imagine I die due to a brain haemorrhage that is incurable today. My body is cryogenically frozen until a cure is discovered. During my time being frozen, an earthquake at the facility results in parts of my brain being broken apart, with some parts of my brain being lost forever. In the future, I am unfrozen, cured, and had all missing parts replaced and broken parts mended. When I wake up, I behave just as I did when I was previously alive.
The question Swinburne asks us is: have I come back to life again?
After considering your answer, think about whether these two thought experiments are comparable. Or are there too many relevant differences?