Philosophers Index Abstract
- In a recent paper, (Mind, Jan. 1997), Chris Hughes argued that on standard views of the identity of artifacts like ships, admitting disassembly, reassembly, and part-replacement, two ships may be in the same place at the same time.
- I show that on Hughes's principles many ships may be in many places at the same time. Metaphysically serious problems arise not for artifacts but for entangled fundamental particles, where collocation of things of a kind appears genuine and unavoidable.
- Irrespective of whether Chris Hughes (1997) has successfully criticised my attempted resolution of the Ship of Theseus1 Problem (of which more below), his own liberality in allowing two ships to be in the same place at the same time has much stranger consequences than he reveals. Following his principles, not only can two ships be in the same place at one time, but one ship can be in two places at the same time, indeed the same places as another ship, and one ship can become two ships. Whatever one may think of Locke's Principle, the principle that two things of the same kind cannot be in the same place at the same time (of this too more below), at the very least, adherence to it blocks this mind-boggling case.
- Hughes's argument depends on two principles:
On this basis he argues as follows. Stathis's ship and Theseus2's ship are exactly alike in the types of their parts and the way these are assembled. (In this they resemble modern mass-produced artifacts, so the issue is by no means merely hypothetical.) Call corresponding parts homologous. Stathis's ship is gradually repaired using homologous parts from Theseus3's ship until the repair is total. By REPL the ship so repaired is Stathis's. By REAS it is Theseus4's. But Stathis's ship is not the same ship as Theseus5's, since their histories are different. So there are two distinct ships in the same place at the same time, contrary to Locke's Principle.
- REPL A ship may survive gradual but total part-replacement.
- REAS A ship may survive disassembly and subsequent reassembly of its parts.
- But now suppose that the parts from Stathis's ship are not discarded but are-placed in their corresponding locations in Theseus6's ship. Then at the end of the process the two ships have totally exchanged all their parts. By Hughes's principles however, Theseus7's ship remains his throughout, and at the end of the exchange of parts it is also Stathis's ship, so Theseus8's ship is now in two places at once, as is Stathis's ship. But at the end, as at the beginning, we have two ships. Both of them are Stathis's ship. And both of them are Theseus9's ship. Hence one ship can become two, and two can become each other while remaining each itself10.
- The problem is worse than that. Where there can be two there can be n. We can imagine a whole armada of a thousand ships, all exactly resembling one another. By suitably juggling their parts, we could arrange for all thousand of them to occupy the space of each of them: each ship becomes a thousand, all hopelessly intertwined.
- The example of total exchange of parts is not new: Chisholm (1976, p. 90 ) says it is "another ancient version of the problem".
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