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Metaphysical possibilities

2010, Egan, Ruth P. K.

Saul Kripke's famous proposal for the necessity of a posteriori identities applies not only to proper names but also to natural kinds, according to Kripke, thus theoretical identifications like 'Water is H2O' are metaphysically necessary truths. He explains the illusion of contingency concerning this necessary identification by suggesting that, while water could not have turned out to be anything other than H2O, it is nevertheless possible that there could have been a phenomenon very like water that was not H2O. David Chalmers' two dimensional semantics provides a framework for the systematic treatment of this possibility concerning what he terms 'watery stuff', such that it is a metaphysical possibility that 'Watery stuff is not H2O' be true. Indeed many other philosophers also view this as metaphysically possible. In this thesis, against both Chalmers and Kripke, I argue that there could not be a phenomenon very like water that was not H2O. After initially analysing each philosopher's claim for the possibility of (non-H2O) watery stuff, I ascertain that it must bear a strong likeness to water and be able to interact with us in a similar manner. Thus, examining what kind of possible world would be required for the claim that there could be watery stuff, I conclude that metaphysically possible, but nomologically impossible, worlds cannot give us watery stuff since nothing in those worlds could be similar enough to water. As for the nomologically possible worlds, nothing other than H2O in those worlds does give us anything like water. Consequently I conclude that there are no metaphysically possible worlds with a phenomenon very like water that is not H2O. I further conclude that the characterisation of Chalmers' primary intension is based on the way the actual world is and, therefore, considering another world as 'actual', contrary to what he claims, has little effect on what extension should be picked out in that world. I briefly examine Kripke's other examples of necessary a posteriori identities and conclude that, in some cases, the possibility which is supposed to explain our illusion of contingency concerning such identities, is also not a genuine possibility. This detailed investigation of the water example, I argue, demonstrates the indispensability of considerations of the properties and laws of the actual world to metaphysical possibility judgements concerning actual phenomena (or similar).