Philosophical Investigations: 347. "But at least I know from my own case what it means 'to say things to oneself'. And if I were deprived of the organs of speech, I could still talk to myself." If I know it only from my own case, then I know only what I call that, not what anyone else does. 348. "These deaf-mutes have learned only a gesture-language, but each of them talks to himself inwardly in a vocal language." -- Now, don't you under- stand that? -- But how do I know whether I understand it?! -- What can I do with this information (if it is such)? The whole idea of understanding smells fishy here. I do not know whether I am to say I understand it or don't under- stand it. I might answer "It's an English sentence; apparently quite in order -- that is, until one wants to do something with it; it has a connexion with other sentences which makes it difficult for us to say that nobody really knows what it tells us; but anyone who has not become calloused by doing philosophy notices that there is something wrong here." 349. "But this supposition surely makes good sense!" -- Yes; in ordinary circumstances these words and this picture have an application with which we are familiar. -- But if we suppose a case in which this application falls away we become as it were conscious for the first time of the nakedness of the words and the picture.