by Bruce E. R. Thompson.
According to the legends of ancient Greece, the city of Athens was once in thrall to the Minoan empire, ruled by King Minos of Crete. Every nine years the Athenians were required to pay a tribute to King Minos consisting of seven maidens and seven lads who were to be used as sacrificial offerings to a terrible monster, the Minotaur, who lived in a labyrinth (which archaeologists speculate may just have been the basement level of the royal palace). Theseus was a young prince, the son of King Aegeus of Athens. Having an adventurous spirit, and having already proven himself adept at slaying rogues and evil-doers, Theseus insisted on being one of the tributes sent to Crete. There Theseus was successful in slaying the Minotaur, rescuing the other tributes, and then sailing back to Athens with them.
There is a great deal more to the story than that. However, a part of the story that is often overlooked is what happened to the ship afterward. Every year the pious Athenians sent a delegation to Delos to consult with the Delphic oracle concerning the will of the gods. To memorialize the victory of Theseus, and possibly to ensure a favorable message from the oracle, the delegation traveled by sea, using the very same ship that Theseus had used to sail to Crete and back. This practice was observed for generation after generation. We have no way of knowing how long this custom lasted, but it can hardly have been less than 1000 years. Theseus (assuming he was a historical figure at all—which seems unlikely) would have lived well before the Trojan War, roughly 1200 B.C.E. Yet the custom of sailing to Delos in the ship of Theseus was still being observed as late as 240 B.C.E. We know this is true because the historian Plutarch mentions the ship being in use “even to the time of Demetrius Phalereus.” Demetrius Phalereus was an orator who was trained at Aristotle’s Lyceum by Aristotle’s successor, Theophrastus.
In 300 B.C.E., some sixty years earlier, Socrates had been sentenced to death. Before the sentence was handed down, however, the ship bearing the delegation to Delos had set sail. Under Athenian law, no executions could be performed while the ship was at sea, since the delegation might conceivably return with news that the gods looked with disfavor on the execution. Hence, the execution of Socrates was delayed by about a month while the ship of Theseus made the two-week journey to Delos and back again. Socrates was only executed after it was confirmed that the gods had not sent back a message to Athens giving him a reprieve.
Time is not kind to wooden ships. To keep the ship of Theseus sea-worthy, the ship occasionally had to be repaired. Rotten planks were taken out and fresh new planks were put in their place. Over the course of generations, it is a near certainty that every piece of wood making up the body of the ship was replaced, perhaps even several times. Metal rusts, so the metal parts must also have been replaced. By the time of Socrates philosophers were beginning to ask whether it was worth continuing the practice of sailing to Delos in the ship of Theseus. Could the ship even still be considered “the ship of Theseus,” when every single part of the ship had not been part of the original ship that made the famous journey to Crete?
This question is important, of course, not because of the ship itself, but because the story is an allegory about us. With every breath we take, we take new molecules into our bodies and breathe out old molecules. Our body is constantly repairing itself with those new molecules. I have been told that every molecule in our bodies is swapped out for a different molecule (of roughly the same type) every three years. I’ve also seen evidence that some molecules are swapped out more slowly. It hardly matters. Even if a complete replacement of parts takes place only over the course of decades, it still follows that we are like the ship of Theseus: constantly being rebuilt from new materials. Hence, just as the ancient Greek philosophers could ask, “How can this still be the same ship?” it makes sense for me to ask, “Am I the same person today that I was when I was born, seven decades ago?”
Some people attempt to answer this question by citing the existence of something called a “soul.” My body may be different over time, but my soul remains the same. But that is an unsatisfying answer. In the first place, no one really knows how to describe what a soul is. What characteristics define a soul? Is it memory? That’s not helpful, since we know our memories are as malleable as our bodies. I know mine is. Is it some other mental characteristic? If so, what characteristic could it be? All our mental characteristics—our personality, our goals, our habits—all change over time. Even if we suppose that there is some “part” of us that does not change over time—call that the soul—is that enough to guarantee that I am the same person over time. Suppose the ship of Theseus had had a golden rudder. Suppose that, over a thousand years, that rudder did not decay and so never needed to be replaced. Suppose that rudder still exists, kept in a museum in London or Oxford. Granted that we still have the same rudder, would that be enough to guarantee that we still have the same ship?
As a graduate student I had the fortune to study under Derek Parfit, one of the foremost experts on what is called “the problem of personal identity.” His view was essentially this: these questions aren’t worth answering. Once we have understood the fact that any entity changes over time in innumerable ways, we have understood all the facts there are to understand. There is no “deep further fact” to be unearthed. So, are you the same person over time or not? Which answer would you like to hear? The facts will remain the same no matter which answer I give. And the facts are that you are constantly changing over time.
I find this view oddly comforting. It helps me confront the reality of death. I cannot greatly fear my own demise when I consider that I, a thing understood to be the same thing over the course of days and decades, never really existed in the first place, and I, a thing understood to be constantly changing, will continue to exist (in changed form) for days and decades and even millennia after I am gone.