 Assuming that Kripke (1971; 1980) is right that water is necessarily H2O, \(\dq{\#}\) has the same extension as \(\dq{\neg}\) in every possible world, and so satisfies the permutation invariance criterion as a matter of necessity (McGee 1996, 578). But intuitively, it does not seem that \(\dq{\#}\) should be counted a logical  constant.[18]