Chapters 4 and 5 were originally published in somewhat different form as "Cambridge Platonists and Locke on Innate Ideas" and "John Locke's 'Doctrine of Signs': A New Metaphysics" in Journal of the History of Ideas (July 1965 and April 1969). Reprinted with the kind permission of Journal of the History of Ideas. Chapter 6 was originally published as "Berkeley's Theory of Signification," copyright by the Regents of the University of California. Reprinted from the Journal of the History of Philosophy, Vol. VII, No. 2, 163-176, by permission of the Regents.