There Is No Metaphysical a Posteriori Necessity

Abstract

Water is H2O. Is it simply so? Or must it be so? Kripke believes the second: If true at all, it must be that water is H2O. What, however, are his reasons why it must be so? Roughly, they are as follows: If two things are identical to each other, then they are necessarily so. The necessity of identity can be proved from the necessity of self-identity and the Leibniz’s Law.