The Ship of Theseus and the Question of Identity

Where does consciousness exist, and what is the reality of our soul if we question the basis of personal identity?

  • The Ship of Theseus was rebuilt over the centuries as wood rotted and broke, so at what point did it stop being the original, and when did it become something else?
    Photo By Fotolia/Netfalls
  • With "The Outer Limits of Reason," Noson S. Yanofsky discusses the limitations of computers, physics, logic, and our own sense of personal identity.
    Cover Courtesy The MIT Press

Within the span of seven years, every cell of your body will die and be replaced—you literally are not the same person you once were. If this is the case, where lies our identity and psyche? Should we be held accountable for the actions of another body, or another mind? These questions, and many more, are contemplated in The Outer Limits of Reason (The MIT Press, 2013). Noson S. Yanofsky considers what cannot be predicted, described, or known, and what will never be understood. In this excerpt from “Philosophical Conundrums,” Yanofsky references the Ship of Theseus before questioning the existence of personal identity.

To find more books that pique our interest,
visit the
Utne Reader Bookshelf.

In ancient Greece, there was a legendary king named Theseus who supposedly founded the city of Athens. Since he fought many naval battles, the people of Athens dedicated a memorial in his honor by preserving his ship in the port. This “ship of Theseus” stayed there for hundreds of years. As time went on, some of the wooden planks of Theseus’ ship started rotting away. To keep the ship nice and complete, the rotting planks were replaced with new planks made of the same material. Here is the key question: If you replace one of the planks, is it still the same ship of Theseus? This question about a mythical ship is the poster child for one of the most interesting problems in all of philosophy, namely the problem of identity. What is a physical object? How do things stay the same even after they change? At what point does an object become different? When we talk about a certain object and say that “it changed,” what exactly is “it”?

What happens if you change two of the ship’s planks? Would that make it somehow less of the original ship than after one plank is changed? What if the ship consists of a hundred planks and forty-nine of the planks are changed? How about fifty-one changed planks? What about changing ninety-nine of the hundred planks? Is the single plank at the bottom of the ship enough to maintain the original lofty status of the ship? And what if all of the planks are changed? If the change is gradual, does the ship still maintain its status as the ship of Theseus? How gradual must the change be?

We are not answering these questions simply because there are no objective correct answers. Some maintain that changing one plank changes the ship and makes it no longer the ship of Theseus. Others claim that as long as there is at least one plank from the original, it is still the original. There are also those who maintain that the changed ship is always the same as the original ship because it has the form of the original. None of these different positions are wrong. However, there is no reason to say that any of them are correct either.

Let us continue asking more questions about our beleaguered boat. What happens if we switch the old wooden planks for more modern plastic planks? Then, as we change more and more of the planks, the ship will be made of a different material than the original. What happens if the people who replace the planks make mistakes in putting in the new planks and the ship has a slightly different form? Another question: Does it matter who is making all these changes to the ship—that is, whether one group of workers does it or another? If the ship is to be preserved for hundreds of years, then surely many different people will have to be making the changes. What if we make so many changes to the boat that it can no longer float out to sea? Can we still call it the ship of mighty Theseus if it cannot perform the same function as the original?

9/18/2020 10:52:52 PM

The Ship of Theseus Paradox is fallacious. Although it is treated as a serious metaphysical question by mature, learned people. “If you replace a part of the ship of Theseus, such a plank in the hull, is it still the Ship of Theseus?” The question can’t be answered until the questioner first answers the question: “What defines the Ship of Theseus?” That should have been the question. To put it another way, when the ship-builder said to Theseus, “I’ve completed the construction of your ship and here’s my bill,” how did Theseus know that the right ship was built?” The asking of the question pre-supposes that there is some intelligent entity out there, somewhere in the universe that assigns identities to things. There is not. The “Identity” of something is assigned by humans. That human is someone who either “owns” the “thing” or is given authority to assign the identity. What happens is this: The authorized human selects characteristics of the thing that are used as the basis for assigning it an identity and giving it a name. Let me give you an example from the aerospace industry where I have some experience. Let’s say that the Acme Aerospace Company designs, builds and tests a rocket engine that works great. We will call it the LR-123. The Air Force wants to buy some for use in a missile. When each rocket engine is delivered, how does the Air Force know it is getting what it paid for? The system created to ensure that is called “Configuration Management.” The identity of the LR-123 is defined by a “drawing tree” and a list of applicable specifications. The drawing tree lists all drawings that define the components and their assembly. The drawings define the dimensions, tolerances, materials, and arrangement. As long as the engine is built in accordance with all the drawings and specifications, it is an LR-123 engine. Now let’s create a “paradox.” Let’s say we have assembled an LR-123 rocket engine in accordance with drawings. In the process of packaging it, a technician accidentally scratches a valve. So, we replace the valve with another one with the same part number. Question: Is it still the LR-123 rocket engine? Yes. The engine satisfies the criteria for its identity. Let’s complicate that. Before the Air Force will accept delivery of each LR-123 engine, it must undergo a test-firing. So, we test fire an engine. It meets acceptance criteria, but in the process of packaging for delivery, a valve is scratched. It is replaced with a valve with an identical part number. Is it still the same engine? No, the replacement valve was not acceptance tested. The basis for identification had changed. The engine has to be retested. Here is a trivial example. A man leaves his house every morning for work. He walks to a nearby intersection where he boards a bus labeled “Route 161.” The bus takes him through town to the building where he works. One morning at the bus stop he notices that when the bus arrives it has a new set of tires. Is it still the “Route 161 bus? Yes. As long as the illuminated panel in the front says, “Route 161” it is that bus. Getting back to the ship of Theseus. To answer the paradox question, Theseus would have to tell us what were the configuration requirements for his ship before he accepted delivery. Did the wood of the planks have to be of a particular variety? If yes, then any changes in planking later on would have to be that wood or it would not be the ship of Theseus. The same question would have to be asked of every other part of the ship. Another example of how identity if assigned by humans. You take a trip to Italy and visit the Colosseum in Rome. You discover when you see it that It has fallen apart over the centuries. Is it still the Colosseum?

5/8/2020 12:11:20 AM

As part of a physical world, we try to reason and address the ourselves with respect to a frame of reference, the human one. The physical world evolves. The evolutionary process is strongly related to the 'Scale of Operation'. The smaller we go, the smaller is the timeframe for evolution. The microbes have even a life span of microseconds. Where as at the other end of large scale structures, the Galaxies have time of change in Lightyears. So the the entire universe is a state of flux, only the reference points for evaluation changes. The time is a tool for convenience and provides measures for evaluation. The human shape is just a combination of mind and body. Though as per Buddha the flux is continuous providing a changing physical entity, the mind body system due to referencing has certain components which slowly change compared physical change. The memory, the experience, the thoughts do change in a reference frame other than physical. So in the realm of mind and body we still remain an entity diffrent than the rest.

3/4/2019 2:28:34 PM

This is more straightforward than it seems. The Ship of Theseus remains the Ship of Theseus regardless of changes in planks or rigging just as I am who I am despite having none of the cells I was born with and none of the character as that has been changed by education and experience. We are who we are because we are recognized by others to be the sum of the histories we leave in our wakes.

Facebook Instagram Twitter