- 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 duplicate1 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.
- In defending his solution to the problem of the ship of Theseus2, 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 Theseus3 case) "we had two ships all along, but not in the same sense of ship", and went on to write that the ship of Theseus4 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 sortal5" 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 Theseus6 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).
Ship of Theseus7: (response to Simons)
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