The Ship of Theseus:
How much change can the identity of a thing tolerate? You might answer: "that depends on the thing," or "that depends on the sort of thing we are talking about." Some philosophers think that there are no standard set criteria that would help to identify each and every thing for a thing of its kind. They believe - these philosophers do - that there are different criteria of identity for different sorts of thing. So, for example, what we think of as the Boston Red Sox may, just may, tolerate much more change in its identity and still be regarded as the Boston Red Sox than, say, an oak tree or a Ford Taurus.
You might wish to take a look at the hand-out on Personal Identity for more of this, for more on cars and teams and rivers and things.
But here - for the nonce* - I want to say a word or two about Theseus' Ship.
Theseus' Ship might be long forgotten but for the fact that philosophers have taken no small pleasure in thinking about its identity over time as an example of how perplexing or problematic the re-identification of a thing can become.
No doubt you remember Theseus. He had the courage to go to Crete, enter the labyrinth and slay the Minotaur, and rescue a number of Athenians who had long been imprisoned there. When he returned to Athens, if you do not recall you can well imagine: he received a hero's welcome.
His ship received a kind of notoriety by association, you might say, and each and every year when a festival was held which included "A Parade of Ships," Theseus would join the parade and stand tall on its fore-deck and wave to the crowd lining the shore, hailed as the man who slew the Minotaur. Indeed Theseus' feat was so highly regarded that his ship continued to be on parade long after he died as a tribute of his grand achievement.
But this is not the part of the story that has so fascinated philosophers.
Imagine that in-between Parades, the crew take Theseus's ship on a tour of the Mediterranean and as they tour the sea, the ship is in need of a few repairs. A storm rips its main sail and so it needs a new sail. Now this plank on the main deck,now that cracks or comes loose and warps in the hot afternoon sun and stand in need of replacement. Pulleys rust and are replaced and rigging snaps and gets re-figured. Now none of this happens over-night. But it does happen over time, over a fairly long time, say, over a number of years.
Now imagine five years have passed and over that (this) period of time every piece of boat, every plank, and every bit of tackle, the pitch and the tar and all the hemp and the rudder, all have been replaced. In fact, the ship now has not one of its original planks or its original pulleys. Indeed it is now made up of new planks and new material. And imagine that the crew take the ship on Parade as is their wont, i.e., as they are inclined, indeed expected, to do, each and every at Festival Time.
Is it Theseus' Ship that is on parade?
Or has it become a different ship and if you believe it has become a different ship, now that all the parts have been replaced, at what point, at what stage in this replacement (repair) process, did Theseus' Ship cease to be Theseus' Ship and become a new and different ship?
Has it, has Theseus' Ship, changed its identity? Suppose you argue that it is the same, this is still Theseus' Ship, on the grounds that it has had one continuous history. Theseus Ship is linked by a succession of spatio-temporal events from the time Theseus himself set sail for Crete to this day, many years later when it is (again) on parade at the Annual Festival of Ships. So, you might conclude "continuity over time" or better, "continuity through time" is the crucial thing.
But now imagine the following, an Athenian entrepreneur has been following behind Theseus' ship all these years and every time a part was discarded or plank jettisoned he was there or one of the many men he hired to keep an eye out was there to pick it up. Now he has all the original bits and pieces of Theseus' Ship. Imagine he has found an old blue-print of the ship that he also picked up at an ancient flea market for next to nothing, say, for two obols, the price, Xenophon tells us in the Memorabilia, of a loaf of bread. Imagine now that our entrepreneur with the aid of the original blue-print manages to put Theseus' Ship ("Hmpty-Dumpty") back together again. Each original piece is back in its original place and aligned with all the other pieces as they were aligned on the day Theseus himself had it in his possession.
Now imagine, too, that our entrepreneur enters this ship in the Annual Festival of Ships and attaches a banner to the stern of the ship so that it streams behind the ship like the banners pulled through the sky behind small aircraft to advertise some event in our day. On this banner he has written in bold, bright letters:
The crew of Theseus' Ship stare across the waters at this "other" ship in shock and disbelief. Many of them have been with the ship on which they stand ever since Theseus, their captain, set sail for Crete.
Who has Theseus Ship?
The entrepreneur or the original crew who have stayed with their ship and repaired it over time?
*O.E.D. "for the nonce": For the occasion; hence (in modern use), for the time being; temporarily.
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