On its polemical side, this work argues against the computationalism of Jerry Fodor, against the behavioural holism of Willard Quine, and against the emergentist and externalist pragmatic realism of Hilary Putnam, to the more general conclusion that analytic philosophy of mind and meaning has cut itself off from the classical tradition of, among others, Locke and Descartes, whose positions did not suffer from the problems besetting these analytic trends. On its positive side, the text offers a theory of mind, meaning and knowledge in the classical tradition. An account of a priori synthetic and a priori analytic knowledge is used to set up a formal system in which modal properties of propositions (such as necessity, possibility, and so forth) can be naturally construed, including the modalities of conditionals and the validity of argument. The author raises the question of the biological implementation of the mind, as a symbolic system, and puts forward the conjecture that mental symbols are implemented in the brain at the genetic level, as patterns of gene expression within certain neural cells. Audience: The book will be of interest to philosophers of mind and meaning, cognitive scientists, logicians, biologists of cognition, linguists, and generally to students of mind and rational processes.