# An incredible coincidence?

According to Peter Simons (1997), my argument against the Lockean principle depends on the following principles:

(REPL) A ship may survive gradual but total part-replacement and

(REAS) A ship may survive disassembly and subsequent reassembly of

its parts.

If, however, (REPL) and (REAS) are both true, Simons argues, then not only can we get two ships in the same place at the same time; we can also get one ship in two places at the same time. To take a case simpler than the one he discusses, suppose I start with a ship, gradually and totally replace its planks--and also gradually and totally reassemble the ship's original planks so that, at the end of the process, we have two duplicate sets of planks, put together in just the same way. By (REPL), Simons holds, the original ship exists (in one place) as a repaired ship; by (REAS), it exists (in another place) as a reassembled ship.

I do not think that (REPL) and (REAS) entail that a ship can be in two places at once. (REPL) and (REAS) are consistent with the following principles:

(REPL+) If a ship has (all) its planks replaced in the right

way (gradually, in the course of the working life of the ship,

with duplicate planks put in the appropriate places, no extra

planks put in, etc.) the ship will survive the planks-replacement,

and will, at the end of the process, be wholly constituted by

the replacing planks (that is, constituted by those planks,

and by no other planks). and

(REAS+) If a ship has (all) its planks taken apart, and those

planks are subsequently put back together in the right sort

of way, the ship will survive the taking apart and putting

back together, and will, at the end of the process, be

wholly constituted by the taken apart and put back together

planks (that is, constituted by those planks,

and by no other planks).

If (REPL+) and (REAS+) are necessary truths, it does seem to follow that a ship could be in two places at once. But then it will also follow that a contradiction can be true-viz., that one and the same ship could be constituted by its original planks, and no others, and constituted by its replacing planks, and no others.

Although (REPL) and (REAS) are consistent with (REPL+) and (REAS+), they do not entail the latter principles; they are also consistent with:

(REPL-) If a ship has (all) its planks replaced in the right way (gradually,

in the course of the working life of the ship, with duplicate

planks put in the appropriate places, no extra planks put in, etc.)

the ship will survive the planks-replacement, and will be, at the

end of the process, at least partly constituted by the replacing

planks. and

(REAS-) If a ship has (all) its planks taken apart, and those planks are

subsequently put back together in the right sort of way, the ship

will survive the taking apart and putting back together, and will

be, at the end of the process, at least partly constituted by the

taken apart and put back together planks.

Even if (REPL-) and (REAS-) are necessary truths, it doesn't follow that ships can be in two places at once, except in the (non-mind-boggling) sense that ships can be partly here and partly there--that is, have some parts here, and some parts there.

Although (REPL-) and (REAS-) are preferable to their plussed counterparts, I don't find them very plausible. In cases like the simple case above, where a ship's original planks are both replaced and reassembled, it does not seem that the end result is a ship that existed all along, and is now (partly) here and (partly) there, The end result is instead two ships, at least one of which did not exist before the replacement and reassembly processes got under way. I am not here denying the existence of entities that are individuated in the way that (REPL-) and (REAS-) says ships are individuated. As far as I can see, there might well be; it's just that they wouldn't be ships, in as much as they are not individuated in the way that ships are individuated.(1)

In fact, my argument against the Lockean principle does not depend on (REPL-) and (REAS-), any more than it depends on (REPL+) and (REAS+). It does depend on the premise that a ship will survive the (right sort of) replacement of its planks cum destruction of its replaced planks, and the premise that a ship will survive plank-disassembly unaccompanied by plank-replacement, and (the right sort of) subsequent reassembly of those planks (see Hughes 1997, p. 53). Simons is aware that one might endorse principles about ship survival weaker than (REPL-) or (REAS-), which allowed ship survival to depend on more than facts about the current constituents of those ships, but he thinks that such principles would be "arbitrary" and not "independently well-motivated". I am not sure just what is wanted here in the way of independent motivation. Intuitively, it seems unproblematic that in a case involving plank-disassembly without plank-replacement, followed by (the right sort of) plank-reassembly, we end up with just one ship-the one we started with. And, intuitively it seems unproblematic (though, not, I think, quite so unproblematic) that in a case involving (the right sort of) plank-replacement, and the destruction of the replaced planks, we again end up with just one ship-the one we started with. On the other hand, in the simple case discussed above, it is obviously false that we end up with one ship wholly constituted by each of two (disjoint) sets of planks, and counterintuitive that we end up with one ship partly constituted by each of two (disjoint) sets of planks. All this seems to me to constitute a motivation to reject principles like (REPL) and (REAS) (in either their plussed or minussed versions), and not to look askance at ship-survival principles that make reference to whether disassembled parts are replaced, or replaced parts are destroyed. The motivation is not independent of our intuitions about ship identity in various actual or possible cases; but why should it be?

In defending his solution to the problem of the ship of Theseus, Simons agrees with me that the ordinary term "ship" is not ambiguous between "form-constant ship" and "matter-constant ship", but protests that he never said it was ("ship", he says, is vague rather than ambiguous). This is puzzling, for Simons wrote that (in the original ship of Theseus case) "we had two ships all along, but not in the same sense of ship", and went on to write that the ship of Theseus problem "uncovers the latent ambiguity in the term 'ship"' (Simons 1987, pp. 202, 203). In any case, I do not see that counterintuitive consequences are avoided by supposing that "ship" is vague, rather than ambiguous. The difficulty--I have argued (Hughes 1997, pp. 57-9)--is that it seems clear that, presuming a ship can survive total replacement of its parts, it can survive total replacement of its parts and subsequent disassembly and reassembly. It is hard to see how this could be so, if, as Simons supposes, no "logically well-behaved sortal" will allow both complete replacement of parts, and disassembly cum subsequent reassembly. Of course, even if this consideration suffices to rule out Simon's solution to the ship of Theseus problem, it does not show that there is anything wrong with the Lockean principle. For as Jonathan Lowe suggested, one could allow the possibility that Simons excludes, and hold on to the Lockean principle, by insisting that only non-re-incorporative reassembly of its previously disassembled but not replaced parts is sufficient for the continued existence of a ship. It's just that I don't find the requirement that reassembly be non-reincorporative intuitively compelling (see Hughes 1997, pp. 59-61).

(1) If there are such things, they constitute a counterexample to the Lockean principle, even if no sortal of ordinary English denotes them.

REFERENCES

Hughes, Christopher 1997: "Same-Kind Coincidence and the Ship of Theseus". Mind, 106, pp. 53-67.

Simons, Peter 1987: Parts: A Study in Ontology. Oxford: Oxford University Press.

Simons, Peter: "On Being the Same Ship(s)--or Electron(s): Reply to Hughes". Mind, 106, pp. 761-7.
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Title Annotation: Printer friendly Cite/link Email Feedback response to article by Peter Simons in this issue, p. 761, on the Ship of Theseus problem Hughes, Christopher Mind Oct 1, 1997 1372 On being the same ship(s) - or electron(s): reply to Hughes. Kantian Ethics Almost Without Apology. Identity Individuation Individuation (Psychology)