Naming and Necessity by Saul Kripke

Kripke’s most important philosophical publication, Naming and Necessity (1980), based on transcripts of three lectures he delivered at Princeton in 1970, changed the course of analytic philosophy. It provided the first cogent account of necessity and possibility as metaphysical concepts, and it distinguished both concepts from the epistemological notions of a posteriori knowledge and a priori knowledge (knowledge acquired through experience and knowledge independent of experience, respectively) and from the linguistic notions of analytic truth and synthetic truth, or truth by virtue of meaning and truth by virtue of fact (see analytic proposition). In the course of making these distinctions, Kripke revived the ancient doctrine of essentialism, according to which objects possess certain properties necessarily—without them the objects would not exist at all.

Proper names are rigid designators.

Saul Kripke