@Joe,
ACB wrote:OK; thanks for the clarification. But I still don't quite see where the possibility of error arises. Before repair, the question 'Spirit or material?' does not arise. After repair, we may answer it as we wish. (We may, of course, wish at the pre-repair stage to look ahead and anticipate our subsequent answer. Post-repair, our actual answer may be different, but that is more a change of mind than an error.)
First off, let me point out that the point of mine that originated this sub-discussion was made before the one where I said we can build whatever objective identities we like, so long as we're consistent. The issue this point addresses is in not knowing which properties define an entity that pre-exists the problem being posed. The identity 'the Theseus' is postulated indirectly in the question; it was not defined by the reader. So in this case we cannot know that, say, physicality is irrelevent (as indeed it may be, depending on this pre-existing identity we've inherited), and hold onto continuity of physicality as part of the solution.
When I speak of defining an identity, I mean stating its complete set of properties. Consistency is then important, so if we define the Theseus before repair, that definition should hold after repair, whatever it may be. This isn't an identity consideration, of course, but one of communication. So, no, I don't think we may answer as we wish - we should be consistent.
ACB wrote:
I wonder if you are over-complicating matters here. Remember that the title of this thread is 'The Ship Theseus'. (What is the 'Theseus'? Answer: A [= one] ship.) Since 1* logically cannot equal 2, I would say that the Theseus cannot be more than one ship; whatever other properties it may have, it has unity necessarily. I think that should be the starting point of any analysis of identity. What we have here is (a) one ship with the continuous form of the original Theseus, (b) one ship with the physicality of the original Theseus, and (c) one (only one) ship which now is the Theseus. If the identity is under-defined, we should say that either ship is the Theseus, not that both are.
What is the Theseus, yes. Shipness is a property I've mentioned before as being possibly the most important, so I'm happy to reject any definitions that allow a Theseus to be anything other than a ship. However, I merely excluded this from the definition. Recall I was demonstrating how choice of properties determines the answer, not actually answering the question posed in the OP.
ACB wrote:
In other words, subjective identities are pragmatic substitutes for the objective identities that we cannot know. Agreed; but how does this point apply to the Theseus case? Here, the problem is not a lack of knowledge (as all the relevant physical facts are observable), but the interpretation of the word 'identity'. The only objective reality here is that one object is being repaired and another constructed from its old parts; which one ends up 'being' the original one is a matter of human attitude, not fact.
Mmm, yes and no. An entity may well be an actual physical system all of whose properties we do not know (i.e. we do not know its objective identity) only the properties we subjectively experience (from which we may build a subjective identity). But we may well define an objective identity as nothing more than a complete set of properties. These may be different to the total set of properties of an actual entity, and so is a different identity. The physical (pre-repair) ship named the Theseus is an entity. It has a complete set of physical properties, not all of which are known. Or the abstraction the Theseus is a complete set of properties we decide on, for instance having 'shipness' and 'continuity of form', among others. Both are equally valid, since the only constraint on an identity is that it uniquely identifies.
ACB wrote:
The repaired ship has an objective spatio-temporal identity, as do its old and new parts individually, and so does the other ship from the time of its assembly. But 'the Theseus' has no objective identity until we define it.
We can define it such that it held at times before we defined it. I don't see a problem with that.
Joe wrote:I mean I guess playing with word definitions could really make it difficult. But I'll take a stab at saying that if reality is what is real, then the most basic way we understand reality is Time and Space. So when questioning what is the reality between the two ships the most widely understood concept would be through chronological order. Meaning the Ship of older parts is the '"Real" Ship i.e. it was built first in time.
Thanks for clarifying, but was it built first in time? It was built after the ship built from new parts, no? You seem to be suggesting it was built
again whereas the ship built from new parts was built only once, but this presupposes the answer to the question as far as I can tell.
