The Ship of Theseus Thought Experiment

The Ship of Theseus, also known as Theseus’ Paradox, is a fascinating thought experiment that has intrigued scholars for centuries. It raises thought-provoking questions about the concept of identity over time. Imagine a scenario where each part of a ship is gradually replaced, one at a time. The fundamental inquiry emerges: Is the vessel that remains after all the replacements the same ship as the one that existed before? Delve into this ancient puzzle and explore the enduring debates it continues to spark.

To begin with, it may be of interest to explore the myth surrounding the Ship of Theseus.

Theseus was a young prince of Athens in Ancient Greece. He was raised away from the kingdom by his mother, Aethra. Upon coming of age, he was told of his true identity as heir to the Athenian throne, and so he set out to claim his birth-right. Reaching Athens, he wanted to find ways of proving his worthiness of succeeding to the throne. To his dismay, he found that the King of Athens, Aegeus, was paying a terrible tribute to the King of Crete, King Minos because he had lost a war to Minos previously.

The tribute was seven girls and seven boys, who were given up to King Minos, to be put in a dangerous Labyrinth, impossible to navigate, and roamed by a ferocious monster, the Minotaur. The Minotaur was a half-man, half-bull, a mythical creature that would devour the boys and girls. Theseus volunteered as tribute to be among the seven boys who were given up to King Minos each year. Theseus had big plans; he wanted to kill the Minotaur, save the children, and stop the tribute.

Here comes the first instance of the ship. King Aegeus was very sad about his son, Theseus, setting sail to potential death, so Theseus promised his father that if he should return, the ship would show white sails. If he perished, the sails would show their normal color, black.

Theseus and the other girls and boys set sail to Crete on their ship, which would be known as the Ship of Theseus. They disembarked at Crete and held an audience with the royal family. Here is where Theseus met Ariadne, the princess of Crete, and the two fell madly in love.

In a secret meeting before entering the maze, Ariadne slipped a ball of thread and a sword to Theseus. He used these gifts to escape, using the sword to kill the Minotaur, and the string to guide himself back out of the maze. Theseus, the other tributes, and Ariadne snuck back onto the ship and set sail to Athens before King Minos could figure out what they had done.

Along the way, the ship of Theseus stopped at the island of Naxos. Here, the story varies in many versions, but Ariadne was left behind, and Theseus left for Athens without her. Ariadne later married the god Dionysus. In distress or ignorance, Theseus then forgot to change the color of the sail, so it remained black. Upon seeing the black sails, King Aegeus was deeply distraught and threw himself from a cliff into the Aegean waters below.

Theseus disembarked from the ship and heard the news of his father’s death. He was very upset but took on the mantle to be the next King of Athens. Then, according to Plutarch, the Ship of Theseus was stored in a museum in Athens, to be a reminder of Theseus’ miraculous feats, and the tragedy of King Aegeus.

Many philosophers, including Heraclitus and Plato, deliberated on the paradox. Plutarch, a biographer, philosopher, and social historian from the 1st century A.D. mentions the paradox of Theseus’ Ship, in his work, the Life of Theseus:

“The ship wherein Theseus and the youth of Athens returned from Crete 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 places, 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.”
(Plutarch, 1st — 2nd century CE)

The paradox is that if the Athenians replaced each plank of the ship with a new piece of wood every time it began to rot, there would eventually come a time when all planks were replaced, and no plank would be from the original ship. Does this mean that the Athenians still have the same ship as Theseus?

Plutarch uses a ship analogy, but the concept applies to any object. If, over time, each component of a thing is replaced, is the object still the same? If not, when did it cease to be itself?

The Ship of Theseus thought experiment has held a strong place in identity metaphysics and calls into question the boundaries and flexibility of identity. Many think that the experiment has no answers, but others have attempted to find a resolution. By considering the ways in which the experiment has been applied, we can gain a better understanding of the Ship of Theseus.

The Living and the Inanimate

The experiment applies not just to inanimate objects like the ‘ship’, but to living beings, too. Consider having two photos side by side of the same person, one picture shows the person in old age and the other picture shows the person in their youth. The experiment asks, how is the person in the two pictures the same, and how are they different?

The body continually regenerates cells, and science tells us that after seven years, the entire body no longer has any of its original cells. Therefore, the human body, just like the Ship of Theseus, has come to be different to its original form, because the old parts have been replaced with new ones to create an entirely new object.

Heraclitus, quoted by Plato in the Cratylus, argued that “all things move and nothing remains still”. This argument maintains that nothing retains its identity, or that identity is a fluid concept, and never one thing for very long. Therefore, neither ship is the original Ship of Theseus.

Regarding the above example, some theorists argue that objects like the ship, are different to a human being because a human has memories, whereas an inanimate object, does not. This comes from John Locke’s theory that it is our memory that links us through time to our past selves.

Therefore, is identity tied to memory, body, neither, or a combination of the two?

Thomas Hobbes steered the Ship of Theseus discussion in a new direction by asking what would happen if after the original material (the rotten planks of the ship) had been discarded, they were collected and reassembled to build a second ship? Would this new, second ship, be the original ship of Theseus, or would the other ship that had been repeatedly fixed still be the Ship of Theseus? Or neither, or both?

This brings us to the theory of transitivity. The theory states that if A = B, and B = C, this means that A must = C. Putting this into practice:  Theseus’ original ship, just harbored, is A. The ship with all the new parts is B. The re-constructed ship is C.  By the law of transitivity, this would mean that all ships are the same and have one identity. But this is nonsensical as there are two distinct ships – the fixed and the re-constructed. There appears to be no concrete answer as to which is the true ship of Theseus.

Thomas Hobbes’ question responds to Plato’s discussion in the Parmenides. He has a similar theory to the transitivity law “one cannot be either ‘other’ or ‘the same’ to itself or another.” This follows on to the idea that the two ‘ships’ can neither be the same, or other, to themselves. As Plato points out, “But we saw that the same was of a nature distinct from that of the one.” This forms a complex argument about the troubling experience of dual identity.

This topic of discussion begun by Thomas Hobbes has continued centuries later, in the contemporary world. Duality of identity is a problem addressed in the modern television series WandaVision which is explored below.

You may have heard of the Ship of Theseus thought experiment in the popular television series WandaVision, part of the Marvel cinematic universe. Clearly, Western thought is still supremely puzzled and intrigued by the paradox.

In the TV series, the character named Vision, is a synthezoid: he has a corporeal body with a mind that is created out of artificial intelligence. Like the ‘ship’ in Theseus’ Paradox, Vision loses his original body, but his memories live on in a replica body. The old components of Vision’s old body are reassembled to create a White Vision. Therefore, this White Vision has the original matter, but not the memories. Whereas the Vision has a new body but retains the memories.

In WandaVision, the Ship of Theseus is summarized thus, “The Ship of Theseus is an artifact in a museum. Over time, its planks of wood rot and are replaced with new planks. When no original plank remains is it still the Ship of Theseus?” 

This draws from Plutarch’s version of the thought experiment, calling into question the identity of the ship. Clearly, there have been no decisive solutions to the paradox from antiquity to the modern era. The ambiguity of the ‘answer’ to the Ship of Theseus thought experiment allows modern audiences to continue to interact and respond to ancient philosophy.

Ship of Theseus: Thomas Hobbes & WandaVision

The television series also includes Thomas Hobbes theory that questions the duality of identity. Vision asks, “Secondly, if those removed planks are restored and reassembled, free of the rot, is that the Ship of Theseus?” This relates to Thomas Hobbes’ idea about reassembling another ship from the discarded parts. The White Vision replies with the paradoxical application of the theory of transitivity: “Neither is the true ship. Both are the true ship.”

Therefore, the two Visions, the one with the memories and a different body, and the other who does not have the memories but has the original body, are both summarised to be one and the same being. But this is impossible because there are two Visions, and they identify differently. Using Plato’s framing, the “nature” of Vision is “distinct from” that of the other one, the White Vision.

The Vision attempts to propose a solution, “Perhaps the rot is the memories. The wear and tear of the voyages. The wood touched by Theseus himself.” This now argues that perhaps neither is the original ship of Theseus, because the original exists only in the memory of Theseus and the people who encountered the very first ship. John Locke’s theory of memory being the creator of identity pieces together the conundrum in WandaVision. The Vision is able to transfer his memories (or ‘data’) to the White Vision, yet the two Visions still identify as separate beings.

WandaVision’s allusion to memory is less of a scientific approach and instead romanticizes the art of thinking. The word philosophy itself means the “love of wisdom,” from philos “love” and sophos “wisdom;” it exercises the thoughts of those who entertain it. The Ship of Theseus thought experiment has certainly exercised many minds from antiquity to now.