Identity and the Ship of Theseus

The Ship of Theseus is a great example of identity, though it does not work for everyone when it comes to personal identity, or the identity of people. Here is the basic idea. A guy named Theseus has a phenomenal ship that everyone wants, but he is not selling for any amount. However, one day, a merchant from a distant land offers Theseus an enormous sum to build an identical ship. The merchant wants the exact same sort of timbers from the same forest, the same nails from, uh, wherever the hell nails come from, the same sail material from the same cotton plants, and so on. If there is a plank of wood that has a knothole in it, the merchant wants an identical knothole in the same place on the duplicate ship. Sounds crazy, right? Well, most rich people are crazy. Theseus agrees and loads his ship with everything he needs to build a duplicate ship and then sets sail. He is only out of port for a couple of hours when one of the planks on his ship warps slightly and allows water into the ship. Theseus could return home and patch it, but he would just as soon get to the merchant, build the duplicate ship and then roll around on his big pile of money. With that in mind, he takes the corresponding piece, its identical counterpart, from the supplies and swaps the two planks out. (If you like, he makes a note of this switch, but his honesty does not matter for how the example works). As the journey continues, he needs to swap out more pieces: sail is torn, carpet is frayed, he needs a new wi-fi router, and so on. For ease of talking points, let’s make the following supposition: Once Theseus is 1/4 through his journey, he has 75% original parts and 25% new parts; at the 1/2 part, he has 50% original parts and 50% new parts; at the 3/4 mark, he has 25% original parts and 75% new parts; and finally, at the end of the journey, he has 0% original parts and 100% new parts.

Here’s the question: is the ship at the end of the voyage the same as the ship at the beginning of the journey? There are only two answers: yes, and no. A bunch of you are going to, somehow, try to wriggle more than that out of the situation, and your insane hearts are in the right place, but that will not make the insanity any less prevalent. Most of you are going to think the ship is not the same, so let’s talk about that first.

If the ship is different (and why wouldn’t be, you are collectively screaming), then when did it become different? At one point on the journey can we point at and say, “There! Did you see that? A different ship!” Here the answers are not so clear, but are not too difficult to lump together. Most people are in one of three categories: a) the very first change; b) right at or after the 50% mark; and c) the final change or replacement of parts. My question to all three groups is basically the same: why there? Why did you pick the percentage mark or the piece that you did?

The ship becomes a different ship at the very first change. This makes sense, I think, until you think about it and whether it makes sense. Suppose the very first change is a nail and not a piece of wood, does that matter? It shouldn’t. The percentage difference between a nail and a plank when the ship is taken as a whole is virtually negligible. What if a bird crapped on the ship? That is a change, but does it make for a different ship?

Of course, not. Bird crap is an extraneous feature of the ship, but is not integral to the identity of the ship itself “Integral”? Very impressive term! So if the ship loses a nail (one pops free), and that nail is not replaced, does that make for a different ship, Mr. Integral? Perhaps the nail was not an integral part, but then what is? If the sail is replaced, does that matter? What if only the hull is replaced? See, the problem is trying to figure out which parts are integral.

We often think of integral parts as though which cannot be taken away and the object still be whatever the hell it is. That can be due to reasons of either identity or function. If we take away the sail of the ship, it still floats and can haul freight (though it takes much longer), and I suspect none of us would have any issue with calling it the same ship. Is the same true if we took away only the hull? Not only would it look the same, but it is not going to float or hold any freight. So far, all of that is fairly intuitive. Let’s take away just the nails. The ship would probably fall apart very quickly, but until it does, is it the same ship? It looks that way and, at least for the moment, it functions in the same way.

Function As Identity
An issue with identity as function is this: Suppose we identify one another by function. First, how the hell do we ever figure out what our function is? If we are using it to fix identity, it cannot be something general like ‘reproduction’ or ‘making money’, because then how would we differentiate between individuals who are doing both or either? Let’s say that we resolve that issue, though, and fix your identity as ‘runner’ because that is what you do when you get any free time, or you are a competing runner or whatever. Dammit, just accept this as your function. Now, suppose you are hurt and can no longer use your legs, and so can no longer run. You can no longer perform the running function — what does that do to your identity? Is it gone? Is it changed?

More than half of the ship must change for the ship to be different: If one little change, even an little integral one, does not make for a different object, then what about a change of 51%? Again, the same questions can be asked: does it matter at all what that extra 1% change is?

Every single piece must change for the ship to be different: I won’t be petty and go rehash the above paragraph again (though I could, because it works). Let’s instead agree that the identity does not change until the last piece is swapped out. Does that make the last piece integral then? What if it is a nail instead of a plank? What if it is a stitch in the sail instead of a nail? Suppose we take that last piece out but do not replace it? 99% of the ship has been changed and the last one percent is just taken away, what does that mean for its identity? Yeah. I know.

Fine, then — the ship does not change. It is the same at the beginning as it is at the end. I can see, now, why you might think that. And everyone who originally thought it are now crowing to the moon about their daringly correct choice. Let’s suppose we now take all of the original parts and put them back together. It would be a fairly crappy ship, but why would that not be the original ship? Yeah. I know.

What you think about the Ship of Theseus might indicate what you think about identity for people. We will see as we continue on this topic in later (though soon upcoming) posts.

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