THROUGHOUT this work I make copious use of ideas of Professor Gilbert Ryle and Mr. P. F. Strawson. Without Ryle's cardinal distinction between knowing-how and knowing-that ( The Concept of Mind, New York, 1949, chap. ii) and many further distinctions drawn in "Ordinary Language" ( Phil. Rev., 1953) I should have been lost. My indebtedness to Strawson "On Referring" (Mind, 1950) is manifest throughout, but especially in my first chapter. Strawson Particular and General (Arist. Soc. Proc., 1953-54) much influenced my later drafts of chapter iii. ( Strawson recent book, Individuals, the subjects of which overlap those of this monograph, arrived too late to affect my final version.)
Other works which have affected the development of the ideas presented here include Plato Parmenides, G. Frege Grundgesetze der Arithmetik ( Jena, 1893), vol. 1, and The Foundations of Arithmetic ( Oxford, 1950), Bertrand Russell "On the Relation of Universals and Particulars" (Arist. Soc. Proc., 1911-12), F. P. Ramsey "Universals", in Foundations of Mathematics ( London, 1931), P. T. Geach "Subject and Predicate" (Mind, 1950), J. L. Austin "How to Talk" (Arist. Soc. Proc., 1953-54), and especially L. Wittgensteins Tractatus LogicoPhilosophicus ( London, 1922), Philosophical Investigations ( Oxford, 1953), and Remarks on the Foundations of Mathematics ( Oxford, 1956).
A special word must be said about the influence of Wittgenstein. I am conscious that he would not approve of what is found here. Wittgenstein, more than anyone, has taught us the great dangers that beset the construction of philosophical theories (despite the fact that he could never entirely restrain his own bent for theory). What I have to offer is nothing but philosophical theory in pretty much the old-fashioned sense. What I owe to Wittgenstein is an appreciation of certain difficulties I should otherwise have missed, and certain key ideas I find in his writings which I use (or misuse) constantly, for example, the idea of a criterion. Had I had earlier opportunity to read and digest Wittgenstein's Remarks on the Foundations of Mathematics, my debt would undoubtedly have been much greater, for that book seems to me to bear sharply on many of the questions I take up in chapters iii and iv. But the book on mathematics did not appear until I was well into a late draft of this monograph; since it was apparent that Wittgenstein's book is anything but easy and not to be quickly absorbed, I decided