Provides comprehensive coverage of logical structure as well as the techniques of formal reasoning.

Modal propositional logic; Modal predicate logic; A survey of modal logic.

Originally published in 1973, this book shows that methods developed for the semantics of systems of formal logic can be successfully applied to problems about the semantics of natural languages; and, moreover, that such methods can take account of features of natural language which have often been thought incapable of formal treatment, such as vagueness, context dependence and metaphorical meaning. Parts 1 and 2 set out a class of formal languages and their semantics. Parts 3 and 4 show that these (...) formal languages are rich enought to be used in the precise description of natural languages. Appendices describe some of the concepts discussed in the text. (shrink)

The first amounts, roughly, to "It is necessarily the case that any President of the U.S. is a citizen of the U.S." But the second says, "the person who in fact is the President of the U.S, has the property of necessarily being a citizen of the U.S," Thus, while (2) is clearly true, it would be reasonable to consider (3) false.

This landmark work provides a systematic introduction to systems of modal logic and stands as the first presentation of what have become central ideas in philosophy of language and metaphysics, from the "new theory of reference" and non-linguistic necessity and essentialism to "Kripke semantics.".

Passages in Leibniz which have been understood to contain his statement of Leibniz law do not in fact contain any statement of that principle. Some of these passages contain a statement of the principle of the identity of indiscernibles, While others contain a statement of a principle about concept identity. The latter principle states that a concept, A, Is identical with a concept, B, If and only if a can be substituted for b in any proposition without change of truth (...) value. (shrink)