A kind of semantics developed by Saul Kripke (1940– ) for modal and intuitionist logic. The distinctive feature of the semantics is that it deploys a set of possible worlds, and formulae are assigned truth values at each world. For modal logics, there is a binary accessibility relation, , which is deployed in the truth conditions for the modal operators, e.g.:
Placing various constraints on generates a wide variety of modal logics. The machinery can be augmented by a collection of non-normal worlds to deliver semantics for an even wider range of modal logics. In intuitionist logic, is required to be transitive and reflexive, and is used in giving the truth conditions of the conditional, thus: