Breaking new ground in the debate about the relation of mind and body, David Armstrong's classic text - first published in 1968 - remains the most compelling and comprehensive statement of the view that the mind is material or physical. In the preface to this new edition, the author reflects on the book's impact and considers it in the light of subsequent developments. He also provides a bibliography of all the key writings to have appeared in the materialist debate.

We discuss first order theories in which individual concepts are admitted as mathematical objects along with the things that reify them. This allows very straightforward formalizations of knowledge, belief, wanting, and necessity in ordinary first order logic without modal operators. Applications are given in philosophy and in artificial intelligence. We do not treat general concepts, and we do not present any full axiomatizations but rather show how various facts can be expressed.