Saul Kripke

Saul Aaron Kripke (born 1940) is an American philosopher and logician now emeritus from (Princeton) and professor of philosophy at CUNY Graduate Center. He has been immensely influential in a number of fields related to logic and philosophy of language. Much of his work remains unpublished or exists only as tape-recordings and privately circulated manuscripts. He is nonetheless widely considered one of the most significant philosophers alive.

Work

Kripke is best known for three contributions to philosophy: semantics for modal (and related) logics, published in several essays beginning while he was in his teens; his 1972 Princeton lectures Naming and Necessity, which significantly restructured philosophy of language and, as some have put it, "made metaphysics respectable again"; and for a controversial and influential interpretation of Wittgenstein.

Modal Logic

Two of Kripke's earlier works (A Completeness Theorem in Modal Logic and Semantical Considerations on Modal Logic) were very influential to modal logic. The most familiar logics in the modal family are constructed from a weak logic called K, named after Kripke because of his contributions to modal logic.

In Semantical Considerations on Modal Logic, published in 1963, Kripke responded to a difficulty with classical quantification theory. The whole motivation for the world-relative approach was to reflect the idea that objects in one world may fail to exist in another. If standard quantifier rulers are used, however, every term must refer to something that exists in all the possible worlds. This seems incompatible with our ordinary practice of using terms to refer to things that only exist contingently.

Kripke's response to this difficulty was to eliminate terms. He gave an example of a system that uses the world-relative interpretation and preserves the classical rules. However, the costs are severe. First, his language is artificially impoverished, and second, the rules for the propositional modal logic must be weakened.

Naming and Necessity

Kripke's three lectures constitute an attack on the descriptivist (Fregean, Russellian) theory of reference with respect to proper names, according to which a name refers to an object by virtue of the name's being associated with a description that the object in turn satisfies. He gave several examples purporting to render descriptivism implausible (e.g., surely Aristotle could have died at age two and so not satisfied any of the descriptions we associate with his name). Kripke proposed instead a causal theory of reference, according to which a name refers to an object by virtue of a causal connection with the object as mediated through communities of speakers. In this way, names are rigid designators: it refers to the named object in every possible world in which the object exists. Causal theories of reference have since been elaborated and developed by Hilary Putnam, Keith Donnelan, Gareth Evans, and others, and are perhaps more widely held than descriptivist theories now. Notable holdouts include John Searle.

Kripke also raised the prospect of a posteriori necessities—facts that are necessarily true, though they can be known only through empirical investigation. Examples include “Hesperus is Phosphorus”, “Cicero is Tully”, and other identity claims where two names refer to the same object.

There is controversy as to whether Kripke was in turn echoing earlier work by Ruth Barcan Marcus in both these ideas.

Finally, Kripke gave an argument against identity materialism in the philosophy of mind, the view that every mental fact is identical with some physical fact (See talk). Kripke argued that the only way to defend this identity is as an a posteriori necessary identity, but that such an identity—e.g., pain is C-fibers firing—could not be necessary, given the possibility of real honest-to-goodness pain that has nothing to do with C-fibers firing. Similar arguments are defended today by David Chalmers.

Wittgenstein

Kripke also made interesting contributions to the study of the later Wittgenstein in lectures published as Wittgenstein on Rules and Private Language, although his work here has been faulted for being not particularly true to the historical Wittgenstein. Indeed, many philosophers refer to the subject of Kripke's book as "Kripkenstein," on the grounds that whoever the text is about, it's not about Wittgenstein. (For alternative readings of Wittgenstein, see for e.g. Colin McGinn's Wittgenstein on Meaning.) Kripke's book has also been faulted for not giving credit to other authors who interpreted Wittgenstein similarly (see e.g. Robert J. Fogelin's Wittgenstein). Kripke's influence has been substantial; much of his work, unfortunately, exists only in tape-recorded or transcript form.

Kripke was the winner of the 2001 Schock Prize in Logic and Philosophy.