Speaking for the Platonist Club, I would like to point out that 'the ship of Theseus' actually constitutes a model. It's like a Ford Meteor, or Boeing 747, albeit with much older technology. But the point about 'a model' is that it can retain its identity qua model, no matter which particular one you're looking at. 'Oh, it's Ship of Theseus, 323 bc model, long keel variation, brass fittings'. So the identity resides in the idea - the actual ship is only an instantiation of that idea.

I disagree here; it would be a "model" in the sense you are outlining, only if there had been more than one Ship of Theseus.

Identity is specific, not generic, so I think you are on the wrong track. Genera has to do with identification, what something is identified as, not with identity as such, which is the logical existence of a unique entity.

Identity is specific, not generic — John

That's what serial numbers are for ;-)

The identity at issue in this thread regarding the ship of Theseus is a relations between particulars. This relations is also called "numerical identity" and can be defined as the relation that each and every particular holds with itself and nothing else. It is what Leibniz's law(s) is (are) about (i.e. the identity of indiscernibles and the somewhat less controversial indiscernibility of identicals). If the identity of A and B were simply a matter of them being instantiations of the same type, then Leibniz's law of identity of indiscernibles would be quite trivial while his law of indiscernibility of identicals would be trivially false rather than trivially true. Wayfarer also would be identical with John, presumably, since both are instanciations of the type "human being".

Also, numerical identity is not a relation that holds between species (as opposed to genera) but rather between particulars (as opposed to universals). The general/specific distinction is not the same as the universal/particular distinction. (Distinguishing clearly those two distinctions has payoffs in the philosophy of law, the philosophy of action, and meta-ethics, as Richard Hare and, following him, David Wiggins, have suggested.)

That would be the ship with all its "accidents"... — apokrisis

Thanks. There is much to agree with in you post, and maybe some to disagree with (or to clarify about my own position) but I must give to what you have written much more thought.

Yes, but they don't guarantee identity since they can be faked. ;)

Wayfarer also would be identical with John, presumably, since both are instanciations of the type "human being". — Pierre-Normand

Well, no. That's why I said the thread is a kind of 'bait and switch'. When it comes to artefacts, such as the proverbial ship, then the matter of identity is different to the nature of the identity of humans. But notice this exchange:

But which one does ''the ship of Theseus'' refer to? A or B

Imagine a person A. Over the course of time his entire being is replaced at the atomic level. — TheMadFool

So that is the 'switch' from 'the ship' to 'a person' . And, note, the assumption that 'an entire being' CAN be replaced by replacing the components, in the same way that an artefact can. So there's an implicit materialist assumption: that personal identity is of the same order as the identity of material objects, whereas I don't know if that is true at all.

That is why, pragmatically, I am able to agree with Aletheist's point about identity, in the case of an artefact, being a matter of designation - because a ship is not a being, but a collection of parts, and as such, has no intrinsic identity. It is what it is, purely as a matter of designation.

Also, numerical identity is not a relation that holds between species (as opposed to genera) but rather between particulars (as opposed to universals). — Pierre-Normand

This is true, and only the particular is absolutely "specific". Both species and genera, as they are employed, are, relatively speaking, both specific and general. The first is specific in regards to species and general in regards to individuals, and the second is specific in regards to genera and general in regards to species.

Note this dialogue, from the Buddhist scripture, 'the questions of King Milinda', which is an account of a meeting between a Greco-Bactrian King (at the time of Alexander the Great) and a Buddhist monk.

the venerable Nâgasena said to Milinda the king: 'You, Sire, have been brought up in great luxury, as beseems your noble birth. If you were to walk this dry weather on the hot and sandy ground, trampling under foot the gritty, gravelly grains of the hard sand, your feet would hurt you. And as your body would be in pain, your mind would be disturbed, and you would experience a sense of bodily suffering. How then did you come, on foot, or in a chariot?'

'I did not come, Sir, on foot. I came in a carriage.'

'Then if you came, Sire, in a carriage, explain to me what that is. Is it the pole that is the chariot?'

'I did not say that.'

'Is it the axle that is the chariot?'

'Certainly not.'

'Is it the wheels, or the framework, or the ropes, or the yoke, or the spokes of the wheels, or the goad, that are the chariot?'

And to all these he still answered no.

'Then is it all these parts of it that are the chariot?'

'No, Sir.'

'But is there anything outside them that is the chariot?'

And still he answered no.

'Then thus, ask as I may, I can discover no chariot. Chariot is a mere empty sound. What then is the chariot you say you came in? It is a falsehood that your Majesty has spoken, an untruth! There is no such thing as a chariot! You are king over all India, a mighty monarch. Of whom then are you afraid that you speak untruth? And he called upon the Yonakas and the brethren to witness, saying: 'Milinda the king here has said that he came by carriage. But when asked in that case to explain what the carriage was, he is unable to establish what he averred. Is it, forsooth, possible to approve him in that?'

When he had thus spoken the five hundred Yonakas shouted their applause, and said to the king: 'Now let your Majesty get out of that if you can!'

And Milinda the king replied to Nâgasena, and said: 'I have spoken no untruth, reverend Sir. It is on account of its having all these things--the pole, and the axle, the wheels, and the framework, the ropes, the yoke, the spokes, and the goad--that it comes under the generally understood term, the designation in common use, of "chariot."'

'Very good! Your Majesty has rightly grasped the meaning of "chariot." And just even so it is on account of all those things you questioned me about-- the thirty-two kinds of organic matter in a human body, and the five constituent elements of being--that I come under the generally understood term, the designation in common use, of "Nâgasena."

That is why, pragmatically, I am able to agree with Aletheist's point about identity, in the case of an artefact, being a matter of designation - because a ship is not a being, but a collection of parts, and as such, has no intrinsic identity. It is what it is, purely as a matter of designation. — Wayfarer

Again, I think this is wrong. All entities have, logically speaking, a unique identity. Whether there is a metaphysically robust identity beyond the purely logical, or what exactly are the metaphysical implications of logical identity, is an entirely different question; one which cannot be definitively answered either by rational or empirical inquiry.

All this shows is that none of the parts are uniquely and separately involved in the identification 'chariot' or uniquely and separately constitute a chariot's identity; they are all uniquely and collectively involved in its logical identity, however. So it also shows how far logic has come since the times of King Milinda.

That is why, pragmatically, I am able to agree with Aletheist's point about identity, in the case of an artefact, being a matter of designation - because a ship is not a being, but a collection of parts, and as such, has no intrinsic identity. It is what it is, purely as a matter of designation. — Wayfarer

That would be to say that artifacts and inanimate objects (such as rocks, planets, storms and rivers) have merely nominal essences while only human beings (and possibly plants and non-rational animals) have real essences. But I thinks that's too sharp a dichotomy. Artifacts and inanimate objects may only have being though their being embedded into the practical form of life of human beings, but that is enough to confer them essences of a stronger sort than merely nominal essences as traditionally conceived, or so it seems to me. Conversely, there also is a need to pragmatize our own essences in something like the Sartrian existentialist fashion. We have some inescapable freedom (however constrained) and responsibility to make ourselves the sort of thing that we essentially are, and not just to build artifacts, or cognitively carve nature, in accordance with our given needs and interests.

All entities have, logically speaking, a unique identity. — John

Which would be what, exactly? What constitutes the identity of a particular tennis ball, or hydrogen atom (for that matter)?

You seem to be saying that the ratio of old planks to new planks is relevant (

not missing say more than 1% of its components...
). But this relevance is tied to the notion of speed (time) of construction/destruction which you agreed is irrelevant. — The Mad Fool

No, it is not tied to that. The requirement is that only one plank be replaced at a time. Those replacements could happen at the rate of one per nanosecond, or one per century. The speed is irrelevant. Just think about playing a video of that process in fast or slow motion. No matter what speed you play it at, it will never look the same as one in which the ship is exploded by a bomb and rebuilt from scratch.

For accuracy and full and open disclosure, the ship that Theseus sailed was constantly changing as he sailed it, though the changes were minor and for the most part the shop remained intact. However, there have been catastrophic changes that now make the original ship a somewhat moot point. But do not despair. Most of the original parts of the ship have been saved and a new ship has been built, using these parts as best as we could muster, understanding full well that there had to be some differences.. If such a re-creation is satisfactory, you may now call this the rebuilt ship of Theseus.

Not a one word answer, but a reasonably clear understanding of what transpired over a period of time. I guess paradoxes may be created when one attempts to tell a story that elapsed over time in one sentence. But really there is no such requirement since time changes everything, some more so than others.

You seem to be making the mistake of asking the metaphysical question and thinking it is the logical question. Logically speaking, the identity of anything at all is constituted by its difference from everything else, and its existence as the particular unique thing that it is.

We have some inescapable freedom (however constrained) and responsibility to make ourselves the sort of thing that we essentially are, and not just to build artifacts, or cognitively carve nature, in accordance with our given needs and interests. — Pierre-Normand

I agree.

That would be to say that artifacts and inanimate objects (such as rocks, planets, storms and rivers) have merely nominal essences while only human beings (and possibly plants and non-rational animals) have real essences. — Pierre-Normand

Maybe humans are designated 'beings' for a reason!

Logically speaking, the identity of anything at all is constituted by its difference from everything else — John

Doesn't that just re-state the law of identity - A=A because it's not everything that isn't A?

The reason I brought up the idea of 'models', is because I think the Platonist insight into the eidos provides a way to understand how something can maintain an identity while also be constantly changing. The 'idea' of the ship is what is real, in that understanding. So you could theoretically produce a blueprint for the ship which dicates its exact attributes and measurements, which can then be made by any builder. So in that sense, the 'real ship' is an idea that the built ship conforms to; the idea, is in some real sense, 'more real' than this or that instance of ship.

And the same principle applies to anything that assumes a form, the form being the blueprint towards which each instance teleonomically strives.

(One of the reasons I think that is important, is because the separation of idea from substance is fundamental to the whole idea of manufacturing and mass design in science and technology. So, I wonder if the reason that the industrial West got the initial idea of mass production which underlies so much of modern technology, because of the Platonic intuition which enabled the separation of the form, the idea, from the substance. Note that the Renaissance and early modern science was marked by a revival of Platonism; and that this is an idea which is generally absent from Indian and Chinese philosophy.)

As to whether the ship is 'the original artefact' - that is really only of interest to 'collectors of artefacts'. I suppose that is a legitimate interest, in that if you're going to spend a million dollars on an artefact, then you want to make sure it's the real thing and not a knock-off. That is where the historical artefact is a different matter to the 'type of thing' - by virtue of it being 'the real one', then it's not simply an instance or a model, but that particular item, the one that was sailed on by Homer, or whoever it might have been.

So you could theoretically produce a blueprint for the ship which dicates its exact attributes and measurements, which can then be made by any builder. So in that sense, the 'real ship' is an idea that the built ship conforms to. — Wayfarer

I think the problem that this doesn't address is that every actual ship (or anything else, man-made or not) has a logical identity in the way which is expressed by the law of identity, as you actually noted. It is by means of that logic that we makes sense of our experience, so we can scarcely discard it, whatever we might think its metaphysical implications are.

I think the problem that this doesn't address is that every actual ship (or anything else, man-made or not) has a logical identity in the way which is expressed by the law of identity, as you actually noted. — John

The answer of course is that the ship
doesn’t exist, that “ship”
is an abstraction, a conception,
an imaginary tarp thrown
across the garden of the real. — Cavacava

That's not too bad as poetry but I don't find the simple explanation that logical identity is a matter of mere abstraction at all convincing. I think identity and difference are immanent in all our concrete practices; they evolve from and reveal our existential/ontological oneness with, and difference from, the world. It won't do to try to dismiss them as mere "abstractions"; I think that would be too facile.

What is this 'logical identity' you keep referring to? The 'laws of thought' (of which the law of identity is one) are abstractions par excellence, basic to the structure of rational thought and language. Whenever we identify something - 'that is a ship' - then we're assigning that object to a class, ships, and then picking it out as 'that ship'. That's how it is given an identity. But the question in this thread is, is 'a particular ship' 'the ship of Theseus'? So I suppose the point of the exercise is that one is trying to nail down identity in terms of a concrete particular - whereas what I have been doing is talking about identity in terms of type, species, etc.

Actually, a case comes to mind. One of my very oldest friends is a world expert marine archeologist. He has been involved in the case of identifying the remains of James Cooks' 'Endeavor', which is thought to rest on the bottom of the harbour of Newport Rhode Island, where it was scuttled after active service. But being a wooden ship, the actual wreckage has mostly rotted away - all that could be expected to be found would be the ballast-stones, and perhaps some brass fittings. But if they're found, then they will be judged 'the real Endeavor'.

No, it is not tied to that. The requirement is that only one plank be replaced at a time. Those replacements could happen at the rate of one per nanosecond, or one per century. The speed is irrelevant. Just think about playing a video of that process in fast or slow motion. No matter what speed you play it at, it will never look the same as one in which the ship is exploded by a bomb and rebuilt from scratch. — andrewk

So, you mean to say that so long as the ship is replaced in small degrees the new ship B also has a valid claim to the sign-the ship of Theseus?

You also say that the time aspect is inconsequential i.e. it doesn't matter whether the destruction/construction took 10 minutes or 100 years. This is probably because you agree with me that the final result is simply indistinguishable - in both cases (10 minutes or 100 years) we end up with ships A and B. How do we proceed now to a solution to the paradox?

If I were to follow your line of reasoning then I'd have to say both ships A and B are referents of "the ship of Theseus? Do you accept this conclusion? If you do then you need two different sets of criteria. One leading to the conclusion that the ship of Theseus is A and another leading to the conclusion the ship of Theseus is B. Wouldn't this be fallacious - specifically the fallacy of equivocation - because we're defining the term ''the ship of Theseus'' in two different ways?

Also, responding specifically to your post, how does the extent of repairs (doing it plank by plank or all at one go) affect the issue? Didn't you agree that it didn't matter if either some or ALL planks were replaced?

What is this 'logical identity' you keep referring to? — Wayfarer

I quality 'identity' with 'logical' in order to indicate that I am not referring to any traditional metaphysical notion of substantive identity or essence (think for example of Aristotle's idea of 'Soul'). But it doesn't follow from this that I must then be referring to something abstract. That kind of either/or thinking is itself mired in traditional philosophical assumptions which I believe have been successfully challenged and superseded by the ideas of the likes of Spinoza, Kant and Hegel and probably Peirce too (although I am as yet not that familiar with his work).

The 'laws of thought' (of which the law of identity is one) are abstractions par excellence, basic to the structure of rational thought and language. — Wayfarer

Is the structure of rational thought and language an abstraction?

It still doesn't answer the question of what you mean by 'logical identity'.

If I were to follow your line of reasoning then I'd have to say both ships A and B are referents of "the ship of Theseus? Do you accept this conclusion? If you do then you need two different sets of criteria. One leading to the conclusion that the ship of Theseus is A and another leading to the conclusion the ship of Theseus is B. Wouldn't this be fallacious - specifically the fallacy of equivocation - because we're defining the term ''the ship of Theseus'' in two different ways? — TheMadFool

As I said above, you need to think about this in the context of a process-based metaphysics. Your question is rooted in an object-based metaphysics, which is incompatible with it.

In the process view, the ship forms a process - similar to what physicists call a worldline. When we say that something is the ship of Theseus, we mean that it is a particular location on that worldline. Both 'ship A' and 'ship B' are locations on the same worldline, so it is valid in both cases to say that it is the ship of Theseus. They are not the same location, but that doesn't matter. What matters is that they are part of the same process. That's why I said that a process metaphysics prevents the sort of paradoxes that can arise in trying to analyse this within an object-based metaphysics.

'logical identity' means the kind of identity which is implied in all our understanding of experience and linguistic usages; it means that the identity of anything consists in its existential difference from everything else, and in its existence as a unique entity. This is repeating what I have already said; what more do you want. I think I know; you are looking for a traditional substantivist explanation of identity.

And you didn't answer my question.

Is the structure of rational thought and language an abstraction? — John

Of course. What else could it be? When you refer to 'ship' you refer to a class of objects. What is a class but an abstraction? All language, maths and logic relies on abstractions.

it means that the identity of anything consists in its existential difference from everything else, and in its existence as a unique entity. — John

That still says nothing more than A = A, and that everything A is A because it is not not A.

If the structure of thought and language is an abstraction then thought and language must also be abstractions. What are they abstracted from?

That still says nothing more than A = A, and that everything A is A because it is not not A. — Wayfarer

Yes and pretty much everything about identity and our experience and understanding of it is implicit in those formulations, which you apparently think are so trivial. You really should read some Hegel some time.

nowhere did I imply or say that they were trivial.

I answered the first question previously.

No, as I explained, I don't agree. Why would you think that completely annihilating an object, and then completely rebuilding a copy of the original object, with the same parts, constitutes having the same object? — Metaphysician Undercover

As children it is common for us to play games. One of these games involves breaking apart toys into its components and then rebuilding. We've all done it and we've seen others do it too. In such cases we never think that the process of annihilation - reconstruction yields a different toy. Are you saying this common sense intuition is wrong?