 The idea of a private language was made famous in philosophy by Ludwig Wittgenstein, who in §243 of his book Philosophical Investigations explained it thus: “The words of this language are to refer to what only the speaker can know — to his immediate private sensations. So another person cannot understand the language.” This is not intended to cover (easily imaginable) cases of recording one’s experiences in a personal code, for such a code, however obscure in fact, could in principle be deciphered. What Wittgenstein had in mind is a language conceived as necessarily comprehensible only to its single originator because the things which define its vocabulary are necessarily inaccessible to others. 