Private Languages

The concerns about subjective truths expressed in my previous post lead naturally to Wittgenstein's 'Private Languages' argument (or at least that version of it which is discussed in Everitt & Fisher's "Modern Epistemology" textbook).

I've tried to formalise the argument as follows:
1) In any genuine language, its words must have genuine meanings.
2) The meaning of a word or sentence is determined by the use which is made of it.
3) Therefore, in any genuine language, there must be a distinction between the correct and incorrect uses of that language. (Else the language would be meaningless)

But suppose there was a private language, one which no-one else could ever possibly understand. Then:
4) Necessarily, the speaker of a private language would be the only person capable of telling the correct from incorrect use.
5) Yet, when evaluating a sentence of the private language, this person would (necessarily) be unable to distinguish between "it seems to me to be so, but really it isn't", and, on the other hand, "it really is so".
6) Hence, necessarily, no-one would be able to distinguish between the correct and incorrect uses of a private language. (From 4 & 5)
7) If it is necessarily impossible for anyone to distinguish between some particular things, then there is no distinction to be made. [premise]
8) Hence, there would be no distinction between the correct and incorrect uses of a private language. (From 6 & 7)
9) Therefore, there could be no genuine private language. (From 3 & 8)

Now, talk about sensations seems to be an attempt at a private language. Your conscious experiences are genuinely private in the sense that nobody else could possibly have access to them. But then, the above argument suggests that you cannot meaningfully refer to those conscious experiences. We can say that 'red' refers to the colour of blood, roses etc, rather than our experience of the colour. But how about the word 'sensation' itself (as used in these contexts)? Is there any way we can save it from pure subjectivity? If not, does that mean that the word 'sensation' is actually meaningless?

That does seem an odd conclusion, since we surely all have at least a rough idea of what 'sensation' means. Presumably we never could have learnt this if it were a truly 'private' word. So it must have some more objective, public meaning. I just can't think what. (Any ideas?)

(Though I'm not entirely certain of premise 2. Maybe we could deny that, to get out of this mess? Dunno. Hopefully I'll be able to add to this after taking Semantics next semester!)