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Has the Ship of Theseus Paradox Changed?

  • Writer: Aidan J
    Aidan J
  • Jul 3, 2018
  • 6 min read

Updated: Jul 3, 2018

If you already know what the Ship of Theseus paradox is, then hopefully you will understand the title.


Trireme, a type of Greek warship that Theseus sailed on.

The Ship of Theseus paradox is an inquiry of a Greek biographer named Plutarch. His most famous work, Parallel Lives, compared prominent citizens and mythological heroes between Greek and Roman society. Since the Roman empire existed much later than Greek city-states, and he compared the lives between those two societies, it should come as no surprise that Plutarch was interested in how things changed overtime. In fact, he used the ship of the founder of Athens, Theseus.


In honor of Theseus, the people of Athens preserved the ship for at least a century. Ships rot, however, and so the citizens had to replace many of the ship parts. Eventually, the ship was completely replaced, leading Plutarch to note:

“This ship became a standing example among the philosophers, for the logical question of things that grow; one side holding that the ship remained the same, and the other contending that it was not the same.”

Thus, the debate over the identity of the ship began. Yet, people were able to solve this paradox, but it just was not convincing enough. For instance, Aristotelian logic (or Aristotle himself) would use his four causes to solve this problem.


  1. The first cause to evaluate is the material cause. The material cause can be simplified to the question, “what?” It is the substance of the material. My desk’s material cause is made of wood. Without wood, this desk would not be my desk, as it would be fundamentally different.

  2. The second cause is the formal cause. This question is “how?” The formal cause of my desk is the blueprint in its assembly. It has a crescent shape, with a shelf underneath, and a support on the outer edge of the crescent and the sides.

  3. The third cause is the efficient cause. This question is “who?” Who made this object? Was it God, was it a carpenter? I don’t know who made my desk, but I do know that one of the efficient causes of this desk was Amazon, who sent it to me.

  4. The fourth cause is the final cause. This question is “why?” I have this desk, so that I can write with a smooth, large surface underneath, and have my computer resting, with perhaps some textbooks on the shelf below. It is made for working.


So, now we must relate it to the Theseus’s ship. The material cause is different, because the wood used is different. The formal cause is the same, because it’s in the same design. The efficient cause is mostly the same. You could say that it was repaired than a different person than who made it, but they were both carpenters still, so it’s not much of a difference. There is still the first efficient cause with the first person who made it, so it does not replace the cause like the material cause does. The formal cause is a little tricky because the intent has not changed since they started preserving it, but it has since Theseus’s use. I am going to say that the formal cause remains the same.


Even though the material is different, Aristotle would say that the formal cause determines a continuous identity in time. The computer that has had all its parts replaced is still the person’s computer, and so it remains that thing. Only the description of the computer has changed, as now it can record and process 4K footage. If I had a metal tree and a natural tree that looked, however, I would not say they are the same, because they never had the same identity.


Thomas Hobbes took this problem a step further. Suppose that the repairmen kept all the replaced parts. After replacing all parts of the ship, they build a “new” ship with the same design and all the same materials. Which ship would be the exact same ship?


Now, the material and formal cause are the same as the original ship, but the efficient cause (or the creator) has completely changed. Furthermore, both ships cannot be identical to the original, as that would make them identical to each other. But there are two ships! Otherwise, we would have the Banach-Tarski paradox on our hands, as that deals more with number conservation. (If you're curious about what this is, you can go to the VSauce video linked below. It's too complex to talk about here.)





Hobbes answered this problem, yet also extended it to a more figurative realm. He claimed a substitution for the part makes it a different version of the boat, meaning that the renovated ship is not the identical boat. If it’s designed the same, made of the same stuff, and made for the same reason, then the product is numerically the same; however, he claims the opposite for people. The body constantly changes, as it sheds skin and deteriorates, yet the man is the same from birth to death due to its constant process of change.


Ever since, people treat the paradox in terms of subjects instead of objects. Instead of knowing the identity of a ship, the focus is now the identity of the person. If we analyze ourselves with Aristotle’s causes, our material cause is the cell (excluding maybe the soul), our formal cause is a bipedal, intelligent mammal (excluding any religious biases), our efficient cause is evolution (excluding the possibility of creationism), and our final cause is still debated (excluding religious biases). We are not sure about any of our causes, we just know that we exist. Thus, this becomes a complex problem to handle.


There’s a variation to this problem by Derek Parfit about a Russian nobleman. This nobleman is a socialist who will inherit land, and thus wants to give away his inheritance; however, he predicts that his opinions will change, and he will no longer follow through. So, he enters a legal contract with his wife, giving her sole authority, and entrusts his decision to her. He also says that she must never listen to his future self, and that she should no longer regard that future self as her husband.


I, too, love my husband only because he’s a socialist.


There’s now a large problem with identity, because if it exists from outside this moment in time, she’ll always disappoint the younger or older husband. If, however, identity exists only in the now, then she will always keep the land because the past husband no longer exists.


Yet, it also begs the questions, does the husband even change? The man is not just his opinion. If that were the case, then my mom would not have recognized me when I decided to wear a jacket to school on a cold day. Instead, she just says, "Thank you for finally listening," or "I told you so."


The husband will still think in the same way that he does. He will probably still cheer for a sports team. He will still snidely tweet about why the opposing political thought is wrong, or whatever the Russian 19th century equivalent is. He doesn't really change, but his opinions do.


The wife can also change though, just as he can, just as anyone can. There is no one certain future that we can count on happening. Not only is it unfair for the nobleman to ask that of his wife, but it's also unfair to assume that of ourselves. The husband is right to plan for the future, but giving away responsibility because he thinks he might change? That's toxic and irresponsible.


Now, this new Russian nobleman problem is bizarre. Not only does it raise questions about morality and identity of a human being, it has much different subject matter, or material, than the Ship of Theseus paradox. It touches on the same issue of identity; that's sort of its design, or the formal cause... wait, so is it the Ship of Theseus paradox? Or is it different? The Ship of Theseus paradox applied to the Ship of Theseus paradox... ouch, that hurts my head.


Here are some resources I used to write this post.





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