Yep, you are. But you are making a conclusion about realism from that. What is your argument for that conclusion? — Banno

Objective features of the world change, and yet the ship that returns is the ship that leaves. It's not the same physical stuff, but it's the same thing. That it's the the same thing is a conceptual/linguistic imposition, a way we view and talk about the world. That's anti-realism. There is no mind-independent fact that determines it to be the same ship. A realist is committed to say that it's a different ship, as the material that leaves isn't the material that returns. — Michael

If we don't see it as the same ship because it's now a plane then it's not the same ship because we don't view it that way. If we don't see it as the same ship because its parts have been replaced (even with similar parts) then it's not the same ship because we don't view it that way. If we see it as the same ship because its parts have been replaced (with similar parts) then it's the same ship because we view it that way. — Michael

On the one hand we have the realist who says that statements are made true by objective features of the world, but what objective features of the world must obtain for the ship that leaves to be the ship that returns? Presumably that the mind-independent material stuff that leaves is the mind-independent material stuff that returns. Which in this case doesn't obtain, and so the realist must commit to "the ship that leaves is the ship that returns" being false. However that might not be a commitment the realist is willing to make, and so they must accept an anti-realist account of "the ship that leaves is the ship that returns" being true; that it's true because we think of the ship that leaves as being the ship that returns. — Michael

Repeating an assertion is not an argument.

Then look to what you first said in this topic:

Speaking very roughly, just to get started, realism holds that ...stuff... is independent of what we say about it; anti-realism, that it isn't. — Banno

And what you said later:

That's specifically the issue - does it count as one ship or two?

And "count as..." is a lexical marker for issues of convention. — Banno

You accept that whether or not there are two ships or is one ship is an issue of convention, i.e. not independent of how we talk (or think) about the ship(s).

If we talk about the Perseus and the Theseus as being the same ship then they're the same ship. If we talk about the Perseus and the Theseus as being different ships then they're different ships. A realist can't agree with this, as set out by you above; according to realism, either the Perseus and the Theseus are the same ship or they're not, whatever we say, and that we can be wrong if we talk about them as being the same (if they're really different) or different (if they're really the same).

There is no mind-independent fact that determines it to be the same ship. A realist is committed to say that it's a different ship, as the material that leaves isn't the material that returns. — Michael

This is in fact demonstrably not true.

There is a mind-independent feature of the boat that remains the same throughout the story: its structure. The boat is a boat of a certain type with certain characteristics and behaviors, and that is all what Theseus needs: a functional, predictable, recognizable boat. Presumably, nobody on that boat cared about the precise atoms or pieces of wood that happened to compose the boat at any given time; these components are expandable and replaceable and do NOT define the boat; not anymore than the water you drink in the morning and pee in the evening does defines who you are.

In other words, a thing is not defined by its components. That would be a reductionist view. A thing is generally best defined by its overall structure and function. So it seems to me that you limit realism to reductionism.

As I've repeatedly said, two different ships can have the same structure. Why is the ship that returns the same ship and not a copy with the same structure?

two different boats can have the same structure. Why is the ship that returns the same ship and not a copy with the same structure? — Michael

It doesn't actually matter, as long as it floats the same way it's functionally the same boat. You can call it a copy of the same structure if you want to, but I don't see what advantage that would bring as compared to calling it the same boat with quite a few pieces changed. And the "copy" wording doesn't really work for living creatures: a tree is not a copy of what it was last year, even though much of its constituents have changed over the year; a person is not a copy of her previous self even though much of her constituents are constantly changing.

The important point is that there are in fact objective features that remains constant in that ship: e.g. structure and functionality. And therefore you cannot say that "There is no mind-independent fact that determines it to be the same ship." It's not true.

It doesn't actually matter, as long as it floats the same way it's functionally the same boat. — Olivier5

Of course it matters. Imagine instead of discarding the replaced pieces they are used to build a second, identical boat. Which of the two boats is the original?

Which of the two boats is the original? — Michael

It doesn't really matter, other than in your mind experiment. They are the same model, bhave the same way; not distinguishable. Who cares which is which?

It doesn't really matter, other than in your mind experiment. They are the same model, bhave the same way; not distinguishable. Who cares which is which? — Olivier5

Philosophers discussing the metaphysics of identity, and whether or not "it's the same ship" is true and if so whether its truth should be understood according to realism or anti-realism, care.

Let me think on it. Seems that you think realism must deny any form of convention, which isn't right. Tomorrow.

Philosophers discussing the metaphysics of identity, and whether or not "it's the same ship" is true and if so whether its truth should be understood according to realism or anti-realism, care. — Michael

You only care about these sorts of questions because you define reality and realism as premised on the 'stuff' objects are made of. But your definitions of realism or reality are arbitrary. They may well come from a certain philosophical tradition or another, but they are arbitrary nevertheless. I personally find your focus on the 'stuff' a bit bizarre and unpractical. In the end, nobody knows what this 'stuff' is... So I define reality and realism differently, it's not about stuffiness for me. I think of it as about mind-independent structure and behavior. That's more practical in my experience.

I think of it as about mind-independent structure and behavior. That's more practical in my experience. — Olivier5

That still doesn't address the question though. Imagine instead of discarding the replaced pieces they are used to build a second, identical ship. Which of the two ships (if either) is the original?

Saying that both ships have a mind-independent structure (of the same type) doesn't help you get at whether one of the two ships is the same (token) ship that left.

To start, you should check out the type-token distinction.

Saying that both ships have a mind-independent structure (of the same type) doesn't help you get at whether one of the two ships is the same (token) ship that left. — Michael

I guess it all depends on what you would call the "same" ship. What does it take in your definition, for a ship to be "the same"? In my definition, structure has to remain similar if not absolutely identical. In your definition, the wood pieces the ship is made of define the ship "sameness".

As per your definition, note that you are not able to distinguish between a pile of wood pieces and a functional ship. You say: as long as the material stuff is the same, it's the same thing, but what if the structure has changed and the material hasn't? Is it still the same ship then? Is it the case that a pile of wood pieces taken of a ship are equal to a ship? No it ain't.

In my definition, structure has to remain similar if not absolutely identical. — Olivier5

In the example of them using the replaced pieces to build a second ship there are two ships with a similar structure to the original. Are they both the same (token) ship that first left?

And if they start building another ship in the shipyard with the same structure as the ship that left, is this new ship also the same ship that had already left for voyage? "We just finished building it yesterday, and it left for Fiji last week". Sounds crazy.

Why don't you answer some of my questions first. What is the difference between a wreck and a functional ship, if not structure?

As per your definition, note that you are not able to distinguish between a pile of wood pieces and a functional ship. As long as the material stuff is the same, it's the same thing, but what if the structure has changed and the material hasn't? Is it still the same ship then? Is a pike of wood piece taken of a ship equal to a ship? No it ain't. — Olivier5

We can say it's the same ship if we like. If I smash a mirror then the broken pieces are the mirror that I used to use to look at myself. If I smash a lamp then the broken pieces are the lamp I used to use to light up my room. The wreckage of the Titanic is the Titanic. The Romandisea Titanic (still being built) isn't (and will never be) the Titanic (that hit an iceberg and sank).

We can say it's the same ship if we like. If I smash a mirror then the broken pieces are the mirror that I used to use to look at myself. If I smash a lamp then the broken pieces are the lamp I used to use to light up my room. — Michael

But it is not called a mirror or a lamp anymore, strangely enough... Things are not defined by their constituents, therefore, but by their structure and function.

If your ship is at the bottom of the ocean due to a hole in the hull, it's not a ship anymore, it's a wreck, and you are probably dead. Structures matter more than constituents.

Things are not defined by their constituents, therefore, but by their structure and function. — Olivier5

Two ships can have the same structure and function, yet they're two ships, not one ship. Again, you're conflating the type-token distinction.

The ship that returns has the same type of structure as the ship that left. But is the ship that returns the same token ship that left? Concluding that it's the same token ship because it has the same type of structure is a non-sequitur, and leads to all sorts of crazy conclusions (e.g. the ship built in Liverpool yesterday being the ship that left for Fiji a week ago).

Two ships can have the same structure and function, yet they're two ships, not one ship. Again, you're conflating the type-token distinction. — Michael

Only types are definable though, tokens are not. You cannot define THAT particular atom of hydrogen. For any practical intent and purpose, it is the exact same atom of hydrogen than any other atom of hydrogen.

Therefore things are not defined by the specific atoms they are made of. It's not the way we human beings define and recognize things, probably because we can't see atoms and if we could, there would be no way to differentiate one atom of carbon from another. So trying to define or recognize a thing or its 'sameness' by looking at which atoms compose it would be highly impractical.

You can identify ships of a same kind though, by their name. The ship that left last week bears a different name than the one built today. Ergo they are recognizably and functionally different.

Only types are definable though, tokens are not. You cannot define THAT particular atom of hydrogen. For any practical intent and purpose, it is the exact same atom of hydrogen than any other atom of hydrogen. — Olivier5

There is more than one hydrogen atom in the universe. The existence of water depends on it. It's two hydrogen atoms and one oxygen atom.

You can identify ships of a same kind though, by their name. The ship that left last week bears a different name than the one built today. Ergo they are recognizably and functionally different. — Olivier5

It might not. They might reuse the name. There are many Olivers and Michaels in the world. The Titanic that was built in Liverpool yesterday isn't the Titanic that sank in 1912, even though they share a name and have the same structure and function.

There is more than one hydrogen atom in the universe. — Michael

Indeed, but they are all identical (isotopes aside) in terms of structure.

There are many Olivers and Michaels in the world. — Michael

My name is actually Olivier, not Oliver.

The Titanic that was built in Liverpool yesterday isn't the Titanic that sank in 1912, even though they share a name and have the same structure and function. — Michael

If they haven't improved on the design, I'm not setting foot on this boat, "different" as it may be. :-)

Indeed, but they are all identical (isotopes aside) in terms of structure. — Olivier5

The same type, but different tokens. When you and I each drink a glass of water we're not drinking from the same glass of water. Even if the two glasses of water have the same structure, there are two different glasses of water. The same with the case of the ship that leaves and the ship that returns. They may have the same structure, but they may be different ships.

Having the same type of structure isn't sufficient to establish token-identity.

They are of course two different glasses in terms of their material constituents and space occupied but people don't actually care for such considerations when they define and recognize things.

For instance, if you propose to me two identical glasses, asking me to chose one, I would say: give me whichever, it makes not difference, it's the same glass anyway (and by that I would mean: the same model of glass).

So, if you apply the word "same" at token level, Theseus left with a ship and came back with another, but if you apply the word at type level, he came back with the exact same ship that he left with. Since types are recognizable but tokens are not, people would generally not waste much breath on discussing token distinctions or token sameness... Distinctions at this level do not amount to any real difference (see the example above with the two identical glasses). So when people speak of sameness, they generally mean type sameness.

They are of course two different glasses in terms of their material constituents and space occupied but people don't actually care for such considerations when they define and recognize things. — Olivier5

Of course they do. If you and I are at the pub each drinking a pint of beer it matters if I'm drinking from your glass or mine.

So, if you apply the word "same" at token level, Theseus left with a ship and came back with another, but if you apply the word at type level, he came back with the exact same ship that he left with. — Olivier5

Whether or not he returns on the same token ship as opposed to the same type of ship is the very issue under discussion. There's a conceptual difference between him leaving on a ship, the ship being repaired over time, and returning, and him leaving on a ship, disembarking, embarking on a sister ship, and returning. In the case of the former we can question whether or not he returned on the same ship, whereas in the latter case we can unambiguously say that he returned on a different ship (even if this sister ship shares the name and the structure of the ship he left on).

Of course they do. If you and I are at the pub each drinking a pint of beer it matters if I'm drinking from your glass or mine. — Michael

Are you trying to be thick? If yes, you're doing well.

Before they get assigned this glass and not another and started using it, they couldn't care less which (clean) glass they were given.

Whether or not he returns on the same token ship as opposed to the same type of ship is the very issue under discussion. — Michael

The answer is fairly obviously and objectively yes for type sameness, and I believe it is moot for token sameness. If Poseidon decided to substitute the ship of Theseus by another of the exact same type in one instant, who would have noticed?

I believe it is moot for token sameness. — Olivier5

Then you're not interested in the philosophical discussion we're having, which is very much about the token sameness.

Indeed I am not interested in moot discussions, but out of curiosity, who is is interested in token sameness, and why?

May I ask: who is is interested in token sameness, and why? — Olivier5

Everyone who considers the ship of Theseus or grandfather's axe and others like it. It has a long tradition in philosophy, going back to Heraclitus and Plato. And in this discussion there's me and Hanover and Banno. We're interested because we're interested in the metaphysics of identity, and on what makes a proposition like "the ship that returned is the same (token) ship that left" either true or false.

We're interested because we're interested in the metaphysics of identity — Michael

Identity is a rather complex question and approaching it through reductionism is not useful, i believe. We living organisms are ships of Theseus, as already explained, and I don't think that we are our atoms because those keep changing all the time. Tokens are by definition replaceable.

Identity is a rather complex question and approaching it through reductionism is not useful, i believe. We living organisms are ships of Theseus, as already explained, and I don't think that we are our atoms because those keep changing all the time. Tokens are by definition replaceable. — Olivier5

And that's precisely why I believe that realism cannot account for token identity in cases like this. Token identity cannot be reduced to the mind-independent "stuff" that makes things up (or their structure). I addressed the issue about living organisms like us here:

There’s certainly a sense in which I’m not the same person I was 20 years ago. I’ve grown and changed as a person - new behaviours and attitudes, likes and dislikes, experiences and memories, and so on. And my material body is not the same that I had 20 years ago, with almost every cell dying and being replaced over time.

But then there is also a sense of continuity, and a linguistic practice of referring to my old self as being my old self. Unless you want to argue for something like a persistent immaterial soul, you can’t make sense of the truth of this by referring to some alleged mind-independent state-of-affairs that such considerations and claims correspond to. It can only be understood according to an anti-realist account (of meaning and truth).

My token identity is maintained, despite the flux of my physical body, by the way I think and talk about myself (and the way others think and talk about me). I'm the same person that was alive 20 years ago because that's how I think and talk about myself. That's anti-realism.