The teenage logician who proved some necessary truths are learned by looking
Saul Kripke published a completeness theorem in modal logic at 18, then spent six decades reshaping how philosophers think about names, necessity and possible worlds. His 1970 Princeton lectures argued that water being H2O is necessary yet discovered by experience, a claim that helped revive metaphysics after logical positivism faded.
Kripke grew up in Omaha, the eldest of three children of Dorothy and Myer Kripke. Accounts of his childhood read like a list of feats: Ancient Hebrew taught to himself by age six, all of Shakespeare by nine, and Descartes plus hard mathematics before elementary school ended. He wrote his first modal completeness theorem at 17 and saw it in print a year later.
At Harvard he took a mathematics degree summa cum laude in 1962, and as a sophomore he was already teaching graduate logic across the river at MIT. He later claimed college taught him nothing he would not have picked up by reading alone. Posts followed at Rockefeller University from 1968 to 1976, a chaired professorship at Princeton from 1978, and from 2002 the CUNY Graduate Center, where he became a distinguished professor in 2003.
His technical legacy is Kripke semantics, also called relational or frame semantics. A model is built from a set of worlds plus an accessibility relation saying which worlds can see which, and the properties of that relation, such as reflexivity or transitivity, pick out different logics. Before this, non-classical logics lacked a model theory; the basic modal system K is named after him, and the method was later adapted to intuitionistic logic.
Naming and Necessity, delivered as lectures in 1970 and issued as a book in 1980, treated proper names as rigid designators that refer to the same object in every possible world, unlike descriptions. It challenged the descriptivist views associated with Frege and Russell and set Kripke against Quine, who rejected modal logic and essentialism. His reading of Wittgenstein on rule-following, nicknamed Kripkenstein, posed a sceptical paradox about meaning. He won the 2001 Schock Prize, left much work unpublished on tapes and manuscripts, and died of pancreatic cancer in Plainsboro, New Jersey, in 2022 at 81.
Source: Saul Kripke
