unbent@ecsvax.UUCP (05/18/84)
==> Finally got a chance to grub through the backlog and what do I find? Another golden oldie from intro philosophy! Whether it's a Greek ship or Lincoln's axe that you take as an example, the problem concerns relationships among several concepts, specifically "part", "whole", and "identity". 'Identical', by the way, is potentially a dangerous term, so philosophers straightaway disambiguate it. In everyday chatter, we have one use which means, roughly, "exactly similar" (as in: "identical twins" or "I had the identical experience last week"). We call that "qualitative identity", or simply speak of exact similarity when we don't want to confuse our students. What it contrasts with is "numerical identity", that is, being one and the same thing encountered at different times or in different contexts. Next we need to notice that whether we've got one and the same thing at different times depends on how we specify the *kind* of "thing" we're talking about. If I have an ornamental brass statuette, melt it down, and cast an ashtray from the metal, then the ashtray is one and the same *quantity of brass* as the statuette, but not one and the same *artifact*. (Analogously, you're one and the same *person* as you were ten years ago, but not exactly similar and not one and the same *collection of molecules*.) It's these two distinctions which ariel!norm was gesturing at--and failing to sort out--in his talk about "metaphysical identity" and "essential sameness". Call the Greek ship as we encounter it before renovation X, the renovated ship consisting entirely of new boards Y, and let the ship made by reassembling the boards successively removed from X be Z. Then we can say, for example, that Z is "qualitatively identical" to X (i.e., exactly similar) and that Z is one and the same *arrangement of boards* as X (i.e., every board of Z, after the renovation, is "numerically identical" to some board of X before the renovation, and the boards are fastened together in the same way at those two times, before and after). The interesting question is: Which *ship*, Y or Z, which we encounter at the later time is "numerically identical to" (i.e., is one and the same *ship* as) the ship X which we encountered at the earlier time? The case for Y runs: changing one board of a ship does not result in a *numerically* different ship, but only a *qualitatively* different one. So X after one replacement is one and the same ship as X before the replacement. By the same principle, X after two replacements is one and the same ship as X after one replacement. But identity is transitive. So X after n replacements is one and the same ship as X before any replacements, for arbitrary n (bounded mathematical induction). The case for Z runs: "A whole is nothing but the sum of its parts." Specifically, a Greek ship is nothing but a collection of boards in a certain arrangement. Now every part of Z is (numerically) identical to a part of X, and the arrangement of the parts of Z (at the later time) is identical to the arrangement of those parts of X (at the earlier time). Ergo, the ship Z is (numerically) identical to the ship X. The argument for Z is fallacious. The reason is that "being a part of" is a temporally conditioned relation. A board is a part of a ship *at a time*. Once it's been removed and replaced, it no longer *is* a part of the ship. It only once *was* a part of the ship. So it's not true that every part of Z *is* (numerically) identical to some part of X. What's true is that every part of Z is a board which once *was* a part of X, i.e., is a *former* part of X. But we have no principle which tells us that "A whole is nothing but the sum of its *former* parts"! (For a complete treatement, see Chapter 4 of my introductory text: THE PRACTICE OF PHILOSOPHY, 2nd edition, Prentice-Hall, 1984.) What does all this have to do with computers' abilities to think, perceive, determine identity, or what have you? The following: Questions of *numerical* identity (across time) can't be settled by appeals to "feature sets" or any such perceptually-oriented considerations. They often depend crucially on the *history* of the item or items involved. If, for example, ship X had been *disassembled* in drydock A and then *reassembled* in drydock B (to produce Z in B), and meanwhile a ship Y had been constructed in drydock A of new boards, using ship X as a *pattern*, it would be Z, not Y, which was (numerically) identical to X. Whew! Sorry to be so long about this, but it's blather about "metaphysical identity" and "essences" which gave us philosophers a bad name in the first place, and I just couldn't let the net go on thinking that Ayn Rand represented the best contemporary thinking on this problem (or on any other problem, for that matter). Yours for clearer concepts, --Jay Rosenberg Dept. of Philosophy ...mcnc!ecsvax!unbent Univ. of North Carolina Chapel Hill, NC 27514