One of the most venerable doctrines in the history of philosophy, linguistics, and psychology is the thesis that words are conventional signs of mental states, principally thoughts and ideas, and that meaning consists in their expression. This expression theory of meaning, as I call it, is firmly entrenched in our commonsense understanding of the world. But familiarity has bred complacency as well as contempt. Development of the doctrine was limited through the nineteenth century, and the twentieth century brought denunciation of the expression theory from generations of scholars. Behavioristic theories of meaning have now faded from view. But referential theories still dominate the field, despite insurmountable problems. This work is an extended effort to clarify, deepen, and defend the expression theory, thereby systematizing what is known about meaning and expression. The best way to do this, I believe, is to carry out the Gricean program, explaining what it is for words to have meaning in terms of speaker meaning and what it is for a speaker to mean something in terms of intention. To succeed in this project, we must develop the theory of thought as a fundamental mental phenomenon distinct from belief and desire, identifying ideas with parts of thoughts. This work, then, is a philosophical treatise on the foundations of semantics.

MEANING AS THE EXPRESSION OF THOUGHT

Like many other central philosophical and scientific ideas, the expression theory was first set out by Plato (427–347 b.c.) and Aristotle (384–322 b.c.).