Can there be a private language, that is, a language that you think in, but never speak to anyone else? According to Wittgenstein, there cannot be, because you would never know whether you are using it correctly. Language is, therefore, an irreducibly public phenomenon. Is it the same with knowledge? Can there be private knowledge? It seems there must be, doesn't there - after all, only you can know whether or not you are actually in pain. Or not? Anyhow, if you enjoy these questions, you will enjoy this thread of discussion on private language at the Philosophy Forums.