The Ship of Theseus | A paradox about meaning of identity

The Ship of Theseus, also known as Theseus’s paradox, is one of the most brilliant ancient thought experiments dealing with the concept of identity. In this article, I will explain the story of the Ship of Theseus and will explore some of the common debates and arguments about this subject.

The story of the Ship of Theseus

Before delving into details, let’s read the original version of the ship’s story as appeared in Plutarch’s book (+/+):

“The ship wherein Theseus and the youth of Athens returned had thirty oars, and was preserved by the Athenians down even to the time of Demetrius Phalereus, for they took away the old planks as they decayed, putting in new and stronger timber in their place, insomuch that 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.”

The Ship of Theseus

The Pluratch’s story is the first known appearance of the Ship of Theseus’ Paradox or Theseus’ Boat as it is sometimes called. Let’s sum up the story so far:

The simple form of Theseus’ paradox (Variation A)

We’ve had a ship and, over time, have changed its parts one by one so that now, we still have the ship. But the question is whether it’s the same ship or a new ship entirely just similar to the old one.

Or let’s put it in another word, as Brian Garret did (+): Can a ship survive the total replacement of its parts?

The story of the Ship of Theseus illustrates various possibilities and paradoxes of identity over time and has attracted the attention of many great philosophers for centuries. Heraclitus, Plato, Hobbes, and Locke are among many other thinkers who have discussed this story in one way or the other over the course of the last two millennia.

The second form of the Thesus paradox

Thomas Hobbes, the great philosopher of the 17th century, posed a new paradox based on this old story. We can call it the second form or the more complex variation of the paradox:

The more complicated form of Theseus’ paradox (Variation B)

Let’s suppose that Athenians piled up the old pranks somewhere, and later on, someone built a ship with them. Now we have two ships docked right next to each other. a new ship that carries the crew on the voyage and a ship with all old original parts. Which one is the Theseus ship?

The answer to the Ship of Theseus paradox

With a brief search on the web, you will different versions of the paradox and various debates over it. Here are a few articles I’d recommend checking:

Before delving into the details of this thought experiment, let’s explore the range of possible interpretations.

It may be easier if we quantify the case. Let’s use the term voyaging ship to denote the ship that started the voyage and has the crew on it. The second ship built with old parts can be called the assembled ship.

Suppose that the voyaging ship has 1000 pranks, and on the voyage, they are changed one by one. It seems that after changing the first prank, nothing serious happens. The voyaging ship is still the same ship with just one tiny change. As we may lose one tooth and implant a new one, and no one would believe that we have changed our identity. The problem becomes serious when all old parts are assembled again, and we have two ships side by side, with similar form and functionality.

There are two choices:

  • The identity is not changed: The voyaging ship is still the voyaging ship. Although there have been changes, but the ship as a whole is something more than its parts, and that’s the real identity of the ship.
  • The identity is changed: The Voyaging ship at the end of the trip is not the same as the ship that started the journey. Now we have a completely new ship.

If we suppose that the identity is not changed. What shall we call the assembled ship? Is it a whole new entity with no relation to the voyaging ship?

On the other hand, if we suppose that the ship’s identity is changed, we face with a serious challenge; time of change. Most of us believe that changing one or two pranks does not change the identity of the ship. So if we believe that the identity changes after changing all1000 pranks, then what can we say about the ship after 999 prank changes? If this is a ship with a new identity, then what about 998 pranks? What about 500 pranks? And what about one prank? So again, we face the challenge of tooth implants!

Theseus’ Paradox in the age of technology

Unlike many old stories and paradoxes that are irrelevant today, the Ship of Theseus Paradox is even more relevant to our contemporary challenges and concerns. Nowadays, the question of identity has just gotten more complicated: How does identity relate to change, augmentation, and enhancement? What does Theseus’ story have to tell about the challenges of post-humanism and trans-humanism?

The artistic manifestation of Theseus’ Paradox

If the Ship of Theseus is too far from your daily experiences and you feel you do not have any intuition about it, there’s a more approachable case. This case is brought up by Shane J. Ralston in KISS and the philosophy.

Questions & Answers

Was there a real ship called the Ship of Theseus?

We don’t know the answer. As mentioned above, what we know about the ship comes from Plutarch’s book. You can find the original text in the archive of Tufts University or MIT’s classics archive.

Which term is correct: Theseus’ Paradox or Ship of Theseus?

In most books and articles, the following terms are used interchangeably: Theseus’ Paradox, Ship of Theseus, Theseus’ Boat, Paradox of Theseus, philosophical boat, Theseus Ship paradox, etc.

But in case that you are sensitive to language delicacies, it’s better to use «Theseus’ Paradox» for the general paradox of identity continuity and consider «The Ship of Theseus» as one of the physical manifestations of the case. As you have seen in the KISS case above, this paradox can have various manifestations in different realms.

It’s not hard to understand why such a thought experiment attracted the attention of great thinkers and philosophers

It may seem irrelevant to the topic of complexity. However, I believe that it has a very simple yet similar idea of illusions like soul and identity that emerged in some of the complex systems (e.g. Humans).


The answer to this thought challenge implicitly answers many other real-world problems. The concept of human identity is just one of them.

Personal identity has been considered a valid construct for thousands of years, although there has never been any convincing definition of the construct.

One of the small yet significant results of understanding the concept of complexity would be finding answers to such tough thought challenges.

The concept of identity is just an illusion. An illusion that has led to many profound misunderstandings and misbehaves and misattributions, and even misdefinitions of the whole world!

In the best case, if you want to be still loyal to this old, ill-defined concept, would be more logical to believe the intransitivity of the identity. It means that the identity changes and evolves and erodes over time, and at any time, it would not be the same as before.

We have the Theseus ship at time t, and Theseus ship at time t+ε, and they have no relationship with each other. At every time step, you can decide once more than what you do mean by the word Theseus and what you’d like to call the Ship.

Aristotle was happy with his explanation of the answer. He divided the changes into two distinct categories: Accidental and Essential.

But who is in the position to distinguish between these two different types of changes? Aristotle the observer! So we are talking about perception and contrary to the well-known statement, here perception has nothing to do with the reality!