Saul Kripke

Saul Kripke (1940–2022) was an American philosopher and logician whose work reshaped modal logic, the theory of reference, and debates about necessity and identity.

Rigid designator: An expression that designates the same object in every possible world where that object exists. Kripke made rigidity central to explaining how names refer across possible worlds.
Naming and Necessity: Saul Kripke’s book, based on his 1970 lectures, arguing that names are rigid designators and that some identities are necessary a posteriori. This work presents his best-known arguments about names, necessity, and identity.
Ruth Barcan Marcus: An American philosopher and logician who pioneered quantified modal logic and defended the necessity of identity. Her work on quantified modal logic anticipated questions Kripke later developed formally.
Necessary a posteriori: A truth that is necessary but knowable only through experience or empirical investigation. Kripke’s identity examples established this category as a central option in metaphysics.
Hesperus and Phosphorus: Ancient names for the evening and morning appearances of Venus, later recognized as names of the same planet. Their identity illustrates how an empirical discovery can reveal a necessary truth.
Possible world: A complete way reality could have been, used to represent modal claims. Kripke’s semantics gave possible worlds a precise role in evaluating necessity and possibility.
Causal theory of reference: A theory holding that a name refers through a historical chain linking its use to an initial naming. Kripke’s account explains how names can refer without encoding descriptions.
Gottlob Frege: A German logician and philosopher whose account of sense and reference became a major framework for theories of names. Kripke’s anti-descriptivist account of names rejects a central Fregean route from sense to reference.
Contingent a priori: A proposition knowable independently of experience that could nevertheless have been false. His discussion of fixed reference showed how stipulations can yield contingent truths known a priori.
Water is H₂O: The chemical identification of ordinary water with the molecular substance H₂O. Kripke uses the case to explain why a scientific identity can be necessary yet discovered empirically.

Linked from 9 pages