Richard asked:

If one has a ship, and one replaces a single part of the ship every year, until all the original parts have
been replaced, is it the same ship?

If so, if you rebuilt the original ship from the removed parts, would the two ships be the same?

If not, at what point did the ship cease being the original ship?

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It depends what you mean by "the same". If you mean "the same object", then obviously the answer
is no in the first case and yes in the second. If you mean, can there be two identical ships, then the
answer is obviously yes. To get any mileage from your questions, you should pre-empt such
ambiguities before you ask. I suspect, in fact, that you're not asking about ships, but about something
else. So beware that your question, whatever its real subject, does relate to objects and not (say) to
designs. Objects can be identical, but numerically distinct. But (for example) if you look at 50 identical
squares on a sheet of paper it can be argued that you're actually looking at just one square, inasmuch
as you're looking at 50 representations of a single concept, not at an object. And if you extend this
idea to embrace biological specimens, the answer is "no" throughout. Thus you could not replace a
spider's limbs with prostheses and proceed as in the ship example. A small matter called death would
intervene somewhere along that line.

Jürgen Lawrenz

Define "same". If "same" means: made of the identical atoms, etc., what is the answer? If "same"
means: looks and functions identically, what is the answer? What definition of "same" do you want?
Pick one, or make one up, and answer the question yourself.

Steven Ravett Brown

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