 Since the 1960s Kripke models, defined below, have served as the basis of the most widely used semantics for all varieties of modal logic. The use of Kripke models in the representation of epistemic concepts involves taking a philosophical stance with respect to those concepts. One widespread interpretation, especially in theoretical economics and theoretical computer science, understands knowledge in terms of informational indistinguishability between possible worlds. What we will refer to here as the indistinguishability interpretation goes back at least to Lehmann (1984).