 Immediately after introducing the idea, Wittgenstein goes on to argue that there cannot be such a language. The importance of drawing philosophers’ attention to a largely unheard-of notion and then arguing that it is unrealizable lies in the fact that an unformulated reliance on the possibility of a private language is arguably essential to mainstream epistemology, philosophy of mind and metaphysics from Descartes to versions of the representational theory of mind which became prominent in late twentieth century cognitive science.