  One might evade this counterexample by appealing to an epistemic modality instead of a metaphysical one. This is McCarthy’s strategy (1987, 439). Even if it is metaphysically necessary that water is H2O, there are presumably epistemically possible worlds, or information states, in which water is not H2O. So if we require that a logical constant be permutation invariant as a matter of epistemic necessity (or a priori), \(\dq{\#}\) does not count as a logical constant. But even on this version of the criterion, a connective like \(\dq{\%}\), defined by