But is it also conceivable that there be a language in which a person could write down or give voice to his inner experiences - his feelings, moods, and so on a for his own use? —– Well, can’t we do so in our ordinary language? - But that is not what I mean. 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.
— PI 243
I have no criterion of correctness. — Luke
Curiously, he only directly refers to "private language" in three passages:
259. Are the rules of the private language impressions of rules?—
The balance on which impressions are weighed is not the impression
of a balance.
269. Let us remember that there are certain criteria in a man's
behaviour for the fact that he does not understand a word: that it
means nothing to him, that he can do nothing with it. And criteria
for his 'thinking he understands', attaching some meaning to the word,
but not the right one. And, lastly, criteria for his understanding the
word right. In the second case one might speak of a subjective understanding. And sounds which no one else understands but which I 'appear to understand'' might be called a "private language".
275. Look at the blue of the sky and say to yourself "How blue
the sky is!"—When you do it spontaneously—without philosophical
intentions—the idea never crosses your mind that this impression of
colour belongs only to you. And you have no hesitation in exclaiming
that to someone else. And if you point at anything as you say the
words you point at the sky. I am saying: you have not the feeling of
pointing-into-yourself, which often accompanies 'naming the sensation' when one is thinking about 'private language'. Nor do you think
that really you ought not to point to the colour with your hand, but
with your attention. (Consider what it means "to point to something
with the attention".)
259 appears to reject an a priori approach to understanding first-person phenomenology in terms of privately defined linguistic definitions (e.g. as in Wittgenstein's Tractatus and Husserl's Logical Investigations)
275 Nevertheless attributes a meaning of sorts to thinking of first-person experience in terms of a private language, namely "the feeling of pointing into yourself when one is thinking about private language"
269 Attributes sense to the notion of "private language" when referring to third-person behaviour.
The arguments against a private language have a more general form that argues against private rules. A rule that is only understood by one person does not count as a rule. — Banno
Only according to Banno and Banno's Wittgenstein
:)
Morals are rules to live by; but if rules cannot be private, morality cannot be private. — Banno
But Wittgenstein stressed the very importance of ethical and aesthetic judgements and railed against the very understanding of aesthetics and morality in terms of linguistic convention. See Wittgenstein's Poker. He in fact rejected the utility and sensicality of reducing ethics and aesthetics to
mere linguistic conventions.
To take a non-moral example, Wittgenstein didn't conclude that a private understanding of redness is impossible because redness is a term belonging to public language whose meaning therefore must refer to public convention. Rather, he concluded that one's private use of the word "red" within a language game cannot be given a meaningful
a priori definition in terms of one's immediate sensations, due to such a definition being a circular tautology that is superfluous to, and likely unrepresentative of, one's actual private use of "red", as well as saying nothing informative to oneself or others.
This doesn't rule out a person discovering, a posteriori , an implicit rule that he discovers to be descriptive of his actual private word usage, only that such a rule cannot be the prescriptive force of his use of the word, due to Humean considerations that reject the platonistic conception of logical necessity.