The Paradox of the ship of Theseus

(Ook beschikbaar in het Nederlands.)

Thought experiment

The Greek historian Plutarch talks in Theseus, 23:1 about the ship of Theseus. Theseus is a sea hero from Greek mythology. He sailed on a ship that was well maintained for many years. All rotten planks were replaced one by one with new planks. Greek philosophers in Athens then asked whether the ship was still the same as the original or whether it is a different version. The philosopher Thomas Hobbes extended this line of thought by using the replaced planks to build a new ship identical to the original. Which copy is now Theseus' ship? This question is explained by many as the question of the identity of ourselves. Our body is constantly changing. What then is our identity and that of the ship? The answer to this cannot be given in classical philosophy, because the criteria to uniquely identify the ship are missing.


Reasoned from the Alforto framework, the answer to the question of which ship is the “real” ship is simple. It begins with the realization that identity is reserved for animals and humans, life forms that move and care for their offspring. Identity is that which is unique or peculiar to someone. Identity is more than a snapshot, a photo. It's about all stages of life, it's more like a movie. Matter and plants do not know the concept of identity. We give a ship a name to uniquely recognize it, but the ship itself has no identity. It cannot take action on its own.


Identity distinguishes one from the other. That's useful if you're a penguin chick, for example, and look the same as thousands of other chicks. Yet you are unique and your mother recognizes you by details such as the sound you make. Your identity makes you unique to your mother and father so that they invest in your future and fulfill their life purpose. The purpose of your identity is therefore clear. You want yourself and your children to survive.


The difference between life and matter is more than a matter of definition. It is a fallacy to apply a concept without agreeing on criteria for its demarcation. Without any criteria, we mix principles from the knowledge domain Behavior with those from the knowledge domain Physical building blocks without us being aware of it. That leads to a lot of pastime, but not to meaningful questions and answers.

Purpose changes

Back to Theseus' ship. The ship itself changes over time, but the goal does not. The goal is maintained by replacing the planks. If we don't do this, the ship will sink. The addition of Hobbes is therefore problematic. Recreating a ship from rejected planks leads to a ship that does not float. We can easily exhibit it in a museum, but that changes the purpose. We can't sail with it, so it's not equal.

Common purpose

Animals and people do have an identity. The body is of course constantly changing, but keeps the same goal from itself and the parents, which is to live. Each life stage builds on previous life stages. People learn every day and therefore constantly change, but the identity remains the same.


By introducing a goal and criteria to define concepts, we create clarity in old issues.

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