LANGUAGE What is the point of the private language argument, and who is it directed against? Wittgenstein once wrote that philosophical therapy is directed against the philosopher in each of us It is quite plausible to propose that each of us, when we begin to philosophize, implicitly believe in a private language Certainly, many first-year students are tempted by the sceptical suggestion ‘For all we know, what I call ‘‘red’’ you call ‘‘green’’ and vice versa.’ This suggestion was at the root of Schlick’s distinction between form and content in protocol sentences, and the whole edifice of logical positivism tumbles down if a private language is impossible So too the epistemologies of Russell and of the earlier Wittgenstein himself But the scope of the private language argument extends much further back in the history of philosophy Descartes, in expressing his philosophical doubt, assumes that my language has meaning while the existence of my own and other bodies remains uncertain Hume thought it possible for thoughts and experiences to be recognized and classified while the existence of the external world is held in suspense Mill and Schopenhauer, in different ways, thought that a man could express the contents of his mind in language while questioning the existence of other minds All of these suppositions are essential to the structure of the philosophy in question, and all of them require the possibility of a private language Both empiricism and idealism entail that the mind has no direct knowledge of anything but its own contents The history of both movements shows that they lead in the direction of solipsism, the doctrine ‘Only I exist’ Wittgenstein’s attack on private definition undercuts solipsism by showing that the possibility of the very language in which it is expressed depends on the existence of the public and social world The destruction of solipsism carries over into a refutation of the empiricism and idealism that inexorably involve it Wittgenstein’s demolition of the notion of a private language was the most significant event in the philosophy of language in the twentieth century After his death, philosophy of language took a different turn because of differing conceptions of the nature of philosophy itself Wittgenstein had made a sharp distinction between science, which is concerned with the acquisition of new information, and philosophy, which sought to provide understanding of what we already know But Quine’s attack on the traditional distinction between analytic and synthetic propositions led many philosophers, particularly in the United States, to 142