This is not what Ray North had bargained for. As an international master criminal he prided himself on being able to get the job done. His latest client had demanded that he steal the famous yacht Theseus, the vessel from which British newspaper magnate Lucas Grub had thrown himself to his death and which more recently had been the scene of the murder of LA rapper Daddy Iced Tea.
But here he was in the dry dock where the boat had just finished being repaired, confronted by two seemingly identical yachts. North turned to the security man, who was being held at gunpoint by one of his cronies.
"If you want to live, you'd better tell me which one of these is the real Theseus," demanded Ray.
"That kinda depends," came the nervous reply. "You see, when we started to repair the ship, we needed to replace lots of parts. Only, we kept all the old parts. But as the work progressed, we ended up replacing virtually everything. When we had finished, some guys thought it would be good to use all the old parts to reconstruct another version of the ship. So that's what we've got. On the left, the Theseus repaired with new parts, and on the right, the Theseus restored from old parts."
"But which one is the genuine Theseus?" demanded Ray.
"I've told you all I know!" screamed the guard, as the crony tightened his grip. Ray scratched his head and started to think about how he could get away with both...
Baggini, J., The Pig That Wants to Be Eaten, 2005, p. 31.
Have you figured out which experiment this is supposed to remind you of? It's a question of the boat's true identity that we are worried about here, so it's a similar problem to the one posed in thought experiment number 2: Beam Me Up. My response to that problem included a passage I wrote during my analysis of John Locke, which I think will be useful to bring up once again. So here it is:
"One helpful analogy is to say identity is like a river. Not the water that flows through it, but the channel that actually forms the river. When storms occur and water is high, the river is deepened. When drought occurs, the river slows and silts up. When earthquakes or glaciers reshape the landscape, the riverbed may hold no water at all. If we know the events that carved the river, we can recognize its identity no matter what state it is in. Likewise, we can recognize identity when we know the events that shaped it. If you know the river and are told the volume of water that will flow its way, you know what the river will look like. If you know a person and are told the events that will occur to them, you will recognize how they handle it. This is how we know people after long absences, and this is how changes during brief separations can surprise us."
So identity is not a fixed, unchanging thing. All people and things undergo metamorphoses over time. Sometimes slowly, sometimes cataclysmically. Words, labels, and categories may be easy to think of as permanent markers, but since the things they represent are always changing, then it follows that these names for things must be changing too.
One of the best examples of this comes from evolutionary biologist Stephen Jay Gould who, after a lifetime of studying fish, concluded that there was no such thing as a fish. "He reasoned that while there are many sea creatures, most of them are not closely related to each other. For example, a salmon is more closely related to a camel than it is to a hagfish." And yet....we all still communicate using the word "fish."
The universe and everything in it are always changing in almost infinitesimally continuous ways. We've developed the branch of mathematics called calculus to help describe these tiny changes, but it would be incredibly difficult to keep track of reality this way by calling everything x, then x1, then x2, then x3, etc. on into infinity. It's much easier for our brains and our languages to just call something X and treat this x as a concrete thing even though it actually has very fuzzy borders at the edges. Thought experiments like this one about the ship Theseus though, serve as excellent reminders of the fuzziness that surrounds us.
So the true identity of Theseus has enlarged. It's now a little bit contained in each of the two new boats, and there are probably pieces of it laying around on the shop floor of the dry dock as well. For legal purposes, an appropriate authority may confer continuity of ownership from one boat to the next, and that might be what the criminal Ray North is concerned with, but that doesn't change the changing nature of Theseus' actual identity.
This may sound like a silly example concerning an imaginary object of little importance, but I for one will try to remember it the next time I meet my friend called "Jane" or "Joe" or "Mary" or "Mike". They've changed since the last time I've seen them, and Jane724 might have something more to teach me than Jane723 did. And then I can become Edxxxx.....