The Quandary
I don’t remember where I read about this, but I found it fascinating. It’s called “The Ship of Theseus.” I relate it here pretty much as I found it, but with some needed editing, so as not to use it word-for-word, and, well, it actually needed editing. At the very bottom I present my personal conclusion. I definitely do not agree with their conclusion at all.
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Taken from “Identity, Persistence, and the Ship of Theseus” (as related on the University of Washington website)
Heraclitus and Plato are the probable instigators to all this “identity crises” related here.
Heraclitus’s “river fragments” raises philosophical concerns about the persistence of identity: under what conditions does an object persist through time as one-and-the-same object? If the world contains things that endure and retain their identity despite undergoing any form of physical alteration, then somehow those things (i.e., the thing’s identity) must also persist through said changes.
Heraclitus had a really good point: can we really step into the exact same river twice…when in reality it continually undergoes changes and the water itself isn’t even the same from one moment to the next?
Specifically, the water at any point changes. At any given time, it’s made up of different component parts from that which it had previously been composed (e.g., the water itself, but also stones, leaves, silt, et cetera). According to one interpretation, Heraclitus concluded that we do not have the exact same river persisting from one moment to the next…so how does a river remain its (“the same”) identity?
According to Plato, Heraclitus maintained that nothing forever retains its identity:
“Heraclitus, you know, says that everything moves on and that nothing is at rest; and, comparing existing things to the flow of a river, he says that you could not step into the same river twice” (Cratylus 402A).
But what Heraclitus might have instead said was:
“On those who enter the same rivers, ever different waters flow.” (fr. 12)
Plato’s interpretation is that it’s not the same river, since the waters are different. But employing a “less paradoxical” interpretation, of course it’s the same river, despite the flow of different water. Both interpretations of Heraclitus defines the Flux Doctrine: Everything is constantly altering; no object retains all of its component parts from one moment to the next.
Okay…so how does the Flux Doctrine handle identity and persistence?
Plato’s interpretation required that Heraclitus apparently practiced what might be called the Mereological Theory of Identity (MTI). This is the view that any physical identity depends on the identity of its component parts. Using math, this may be viewed as:
For and all compound objects, x and y, x = y only if every part of x is a part of y, and every part of y is a part of x.
I.e., an object continues to exist (from time t1 to time t2) only if it is composed of all the same components at t2 as it was composed of at t1.
Therefore, sameness of parts is a necessary condition of identity.
Sounds sane, right?
But what if we want to allow an object to persist through time in spite of a change to some of its components? Must we then deny MTI?
An object x, existing at time t1, can be numerically identical to an object y, existing at time t2, even though x and y are not composed of exactly the same parts.
But once you deny MTI, where do you draw the line? (I feel any time you employ mathematics, you’re automatically limiting philosophy, but I’m running with what’s being presented for now….)
Denying MTI leaves this discussion vulnerable to shoot-me-now puzzles, the mother of them all being:
The Ship of Theseus
This is a puzzle that’s been around since about the time of Heraclitus (535 BCE – 475 BCE), maybe after. It’s first apparent mention is by Plutarch (46 CE – 119 CE ), in Vita Thesei, 22-23:
“The ship wherein Theseus and the youth of Athens returned 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 place, 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 states that the ship was exhibited during the lifetime of Demetrius Phalereus (ca. 350-280 BCE). Demetrius was a well-known Athenian and a student of Aristotle, in his Peripatetic school. Demetrius also wrote some 45 books. He was also a politician.
The original quandary is:
Though the original ship of Theseus had been decaying, each of its decaying planks had been replaced over many years to keep it seaworthy. Eventually (the tale goes), not a single plank from the original ship remained.
Think about that. No, really, think about it given all we’ve said so far.
This being the case…did the Athenians still have the one and true Ship of Theseus that originally belonged to Theseus?
I have my answer. Do you?
But, wait—there’s more! That one question would be far too easy to answer!
The quandary is livened up by:
There are two different modernized versions of The Theseus Ship gedankenexperiment. On both versions, plank replacements are taking place at sea. Theseus sails away…replaces each and every plank on board with a new plank (yeah, of course, in this gedankenexperiment Theseus carries all he needs to do this, including replacement parts—just don’t think too hard about this part, okay?, it’s mind game).
Two modernized gedankenexperiment versions are:
- Simple version: Theseus completely rebuilds his ship, by replacing all the old parts with new ones, throwing the old ones overboard.
- Does he arrive to his home port on the same ship as the one he left on? Of course the ship has changed, so is the rebuilt one really still the same one Theseus and his crew left on? Here we go with the math thing again…
- Let A = the ship Theseus originally started his voyage with
Let B = the ship Theseus ended up finishing his voyage with
- Is the question simply A = B? If not, why not? Suppose Theseus had left one original part in. Would that have been enough to make A identical to B? If not, suppose he had left two pieces…where do we draw the line?
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- Not-Simple version: Use the Simple Version, but add: following Theseus in another boat; call it the Scavenger. The Scavenger takes all the discarded pieces Theseus threw away and rebuilds the Ship of Theseus all over again! Then some of the Scavenger’s crew sails the rebuilt Ship of Theseus back to its home port (remember, this ship is composed of precisely and exactly all the original parts that composed the ship Theseus started out in). The Scavenger docks this rebuilt Theseus Ship right next to one that Theseus rebuilt as his new ship. So, back to misleading mathematical equations…:
- Let C = the rebuilt Theseus ship some of the Scavenger’s crew finished the voyage with.
Is your mind beginning to hurt?
How do we sort out the Theseus identities of ships A, B, and C?
Two alternatives to the modernized gedankenexperiment versions are:
- Employing MTI tells us that A = C. There are three ships: Ship A was sailed out by Theseus. Ship B was created from the systematic dismantling of Ship A with new parts. Ship C was Ship A cobbled back together from it dismantled and discarded parts. “Ships” A, B, and C all returned to port. Ship B was berthed directly beside Ship C and are “identical” to each other.
- Not employing MTI tells us that A = B. Doing this we still have two ships, but their identity and non-identity relations are different: Ship A was sailed out by Theseus, but Ship B was sailed in by Theseus. That other, Ship C, was created out of Ship A‘s original parts during the voyage, and was also sailed back into port.
The thought is that both alternatives lead to unintuitive consequences. But do they?
- The problem with alternative (i) is that it requires Theseus to have changed ships during the voyage. For he ends up on Ship B, which is clearly not identical to C. But Theseus never once got off his ship during its entire voyage: Theseus got on board a ship (A), sailed a voyage during which he never got off said ship, and arrived at his destination in a ship (B). He was on just one ship during the whole process, but alternative (i) seems to require that he was on two (dare we say three?) different ships.
- The problem with alternative (ii) is that if we say A = B we must also say that B = C , which (according to those who wrote this up say) also holds that A = C . Yet every part of A is a part of C, and every part of C is a part of A! So A and C are two different ships even though their parts are the same. But what say you of A and B? They have no parts in common, yet A and B are the same ship (according to those who wrote this up). These results seem as paradoxical as the view that there are no persisting objects.
Conclusion – Theirs
MTI seems too strong. It denies identity to objects that we think of as persisting through time. But that leaves us with problems:
- What do we replace it with? Spatio-temporal continuity (the intuition behind our alternative (ii), above)? According those-who-wrote-this-up, that seems the most promising (and common) answer. A persisting object must trace a continuous path through space-time. And tracing a continuous path is compatible with a change of parts, so long as the change is gradual and the form or shape of the object is preserved through the changes of its component materials. So it appears that we can replace MTI with the theory of spatio-temporal continuity (STC). Man, it all depends what you define as constants.
- But STC is also problematic. For it is easy to imagine cases in which our intuitions tell us that we have numerical identity without spatio-temporal continuity. Consider that an object can be disassembled and then reassembled (Consider a UFO taken apart and its parts, placed in different shipping boxes, are sent across country. The boxes are then unpacked and the UFO reassembled). How do we account for its identity? STC breaks down in this case, for there is no continuously existing UFO-shaped object tracing a smooth path through space-time. But MTI gives us the right result: the reassembled UFO is made of exactly the same parts as the one that was taken apart, and so is numerically the same UFO. In fact, there is a way of describing the case of Theseus’s ship that seems to demand MTI rather than STC. Suppose the ship (A) is in a museum, and a band of covert operatives steals the UFO by removing its pieces one at a time and reassembling them elsewhere.* Each day, the thieves remove another piece, and replace it with a look-alike. When they have removed all the original pieces, we are left with this situation. There is a ship, B, that is in the museum (made of all new materials), and there is a ship, C, in the possession of the thieves (the original pieces of A now reassembled). Which ship is A (Theseus’s original ship)? Surely not B—it’s just a copy of A, left behind in the museum by the crooks to cover up their crime. It is C that will interest the antique dealer who is interested in buying A, the original ship.
The authors of this presentation maintain they are still baffled and therefore still trying to work it out.
*Any similarity to covert government operations or operators is purely coincidental and I deny everything.
My Conclusion
Occum’s Razor. Sometimes the simplest answer is the answer.
And keep math out of it, unless there is some Mathematical Kung-fu that allows for notional variables, which I just can’t think of right now, short of some XXYZ element. In any event and first off:
- Ship A does not equal Ship C. While the ships are physically the same, they are not notionally—nor intentionally—the same (“identical”). It’s like how Eskimos have many terms for “snow.” Intent is everything in life. Nor is Ship C identical to Ship B! Ship A was old and decrepit and needed to be repaired, which turned into Ship B (BRAND NEW!). Ships A’s old boards had been tossed, but salvaged and rebuilt into Ship C. Ship B was BRAND NEW. Details, my friends, details….
- However, “Ship C” is in fact Ship A. If any of the three ships could be said to be the same, it is A and C. Ship A was torn apart…then rebuilt. Those two physical constructs are the same. Their identities are not. Now, I can still split hairs, here, when I get into my “Identity” details, below, but physically, Ship C IS Ship A. Therefore there should be no “Ship C” in this whole thing.
- Ship A is NOT the same as Ship B. See item #1, above. Please. Ship A = old and decrepit. Ship B = BRAND NEW. Not the same. They just both happen to bear the same “applied name.
- NO, he wasn’t on just one ship during his voyage. Don’t be led down the primrose path by the argument above. He was on two ships, unless he walked aboard “Ship C” while in port. When you break down the above argument it deconstructs into the following:
- Theseus initially departed on one ship.
- The ship Theseus initially departed on was falling apart so a new ship was built under their very feet as they sailed.
- This is a TOTALLY NEW SHIP
- Built from TOTALLY NEW MATERIAL
- The old/original ship’s material was thrown into the ocean. Trash.
- Another ship sailed behind them.
- That ship collected all that tossed trash.
- This other ship’s crew decided to mess with Theseus and his crew.
- They rebuilt the decrepit trashed parts and played a nasty head game on Theseus and the world.
- All three ships returned to harbor:
- The original and reconstructed, decrepit Ship of Theseus.
- The totally new ship, now called The Ship of Theseus.
- The Scavenger.
The Flux Doctrine
I’m pretty much in agreement, here. Everything is constantly in motion. On atomic and sub-atomic levels this is just how it is. Atomic and subatomic particles are always in motion. Well, for the most part…there is a halt to all movement at zero degrees Kelvin…as I remember my university physics. Anyway, here I do believe absolutely everything is always in a state of change. But even at a macro level we see this with the decay of all objects over a period of time.
Identity
When it comes to identity, things can get weird, if you employ limiting constructs. Like basic math.
We all identify THINGS by nomenclatures. It one of the ways we manipulate and identify matter on the Corporal Plane. When things are simple, the minute details don’t really matter, pardon the pun. But when you begin to closely examine anything corporeal (like in Philosophy or science or high math), you do note that everything is indeed, not as it macro-ly appears. And, for the most part, it doesn’t matter. But in this case, it do, just like to the Eskimos there are many types of snow that don’t just conform to physics. There are interpretive versions, as well.
In this Theseus gedankenexperiment each ship is different because each has not only a different physicality/physics, but a different intent/interpretation. Only one ship was the original. That one was then torn apart and tossed away, but later rebuilt. Ergo and therefore, the owners no longer gave the intent or interpretation of that ship as THEIR operational ship. Therefore it no longer is the “Ship of Theseus.” It has now become a ship of Theseus…or trash, if not rebuilt by that prankster crew of the Scavenger.
The ship that had been juxta positionally rebuilt under the crew’s feet is now the Ship of Theseus. Period.
And, by the way, since “Ship C” was used as a prank (ha-ha, those kidders!), it would also have its own Eskimo name of something more like The Kripyaship of Theseus. Take that, Aristotle…or Socrates—Plato? Ah, hell, they all look alike….
It doesn’t always appear that intent matters, but it does! When you look at anything (food, clothes, someone saving you from drowning, a lawyer trying to prove you’re guilty of a crime…) close enough…intent always matters. I’m assuming you’d prefer to eat something that was intended to be created as nourishing food rather than debilitating or murderous poison.
Hopefully I kept my thoughts straight and didn’t talk myself into a corner…but I’m sure any issues will be suitably pointed out….