Saul Kripke

Saul Aaron Kripke (b. 1940, Omaha, Nebraska, Nebraska) 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 Much of his work remains unpublished or exists only as tape-recordings and privately circulated manuscripts.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, and was the winner of the 2001 Schock Prize in Logic and Philosophy.

Truth

In his 1975 article "Outline of a Theory of Truth", Kripke showed that a language can consistently contain its own truth predicate, which was deemed impossible by Alfred Tarski, a pioneer in the area of formal theories of truth. The trick involves letting truth be a partially defined property over the set of grammatically well-formed sentences in the language. Kripke showed how to do this recursively by starting from the set of expressions in a language which do not contain the truth predicate, defining a truth predicate over just that segment: this adds new sentences to the language, and truth is in turn defined for all of them. Unlike Tarski's approach, however, Kripke lets "truth" be the union of all of these definition-stages; after a denumerable infinity of steps the language reaches a "fixed point" such that using Kripke's method to expand the truth-predicate does not change the language any further. Such a fixed point can then be taken as the basic form of a natural language containing its own truth predicate. But this predicate is undefined for any sentences that do not, so to speak, "bottom out" in simpler sentences not containing a truth predicate. That is, "'Snow is white' is true" is well-defined, as is "'"Snow is white" is true' is true," and so forth, but neither "This sentence is true" nor "This sentence is not true" receive truth-conditions; they are, in Kripke's terms, "ungrounded."

Related Topics:
Truth - Alfred Tarski

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