How did Wittgenstein "cure" Anscombe of phenomenalism?

Question

In "Collected Philosophical Papers Volume 2: Metaphysics and the Philosophy of Mind", Elizabeth Anscombe wrote the following:

I always hated phenomenalism and felt trapped by it. I couldn’t see my way out of it but I didn’t believe it. It was no good pointing to difficulties about it, things which Russell found wrong with it, for example. The strength, the central nerve of it remained alive and raged achingly. It was only in Wittgenstein’s classes in 1944 that I saw the nerve being extracted, the central thought “I have got this, and I define ‘yellow’ (say) as this” being effectively attacked. –At one point in these classes Wittgenstein was discussing the interpretation of the sign-post, and it burst upon me that the way you go by it is the final interpretation. At another I came out with “But I still want to say: Blue is there.” Older hands smiled or laughed but Wittgenstein checked them by taking it seriously, saying “Let me think what medicine you need… . Suppose that we had the word 'painy’ as a word for the property of some surfaces.” The 'medicine’ was effective, and the story illustrates Wittgenstein’s ability to understand the thought that was offered to him in objection. One might protest, indeed, that there is this wrong with Locke’s assimilation of secondary qualities to pain: you can sketch the functioning of “pain” as a word for a secondary quality, but you can’t do the reverse operation. But the 'medicine’ did not imply that you could. If “painy” were a possible secondary quality word, then wouldn’t just the same motive drive me to say: “Painy is there” as drove me to say “Blue is there”? I did not mean “'Blue’ is the name of this sensation which I am having,” nor did I switch to that thought.

I find this passage a bit obscure, and I was hoping someone could flesh out a bit more exactly what argument Wittgenstein was making here.

EDIT: I should clarify what I'm looking for. I understand what she means by "the way you go by it is the final interpretation." What I don't understand is the argument being made in "Suppose that we had the word 'painy’ as a word for the property of some surfaces."

Answer 1

Wittgenstein's therapy is (in essence) a technique for 'un-asking' a question (or 'un-saying' a statement) that leads us into pointless philosophizing. The trick is to examine a problem for language errors — or more precisely, to look for moments in our problematic where we have misused or broken the rules of the language game we are engaged in — in the understanding that once we've seen the language error the problem itself will disappear and cease to trouble us. To use Wittgenstein's game analogy, imagine you and a friend are playing chess, and your friend takes his king, jumps it diagonally over your queen, and then removes your queen from the board. You might say to your friend: "No, you've made an error: that is how a king moves in the game of checkers, not how it moves in the game of chess". Then you can restore the board and get back to the game. Wittgenstein argues that we make these kinds of errors frequently in language use, shifting from one language game to another and shifting the rules by which words and phrases are meant to operate.

In phenomenalism (as noted in the comments, above) statements about objects are considered to be synonymous with statements about (potential) sense data. A statement about a 'blue cube' says nothing more or less than a statement about the sensory data that produces the image of a 'blue cube' in our heads. Phenomenalism doesn't suggest that the blue cube exists out there in the world; it merely implies a kind of continuity to sensory experience. In other words, if I have the sensory experience of a blue cube and I close my eyes, the potential for having that sensory experience is still there; there's a possibility that when I open my eyes I will once again have the sensory experience of a blue cube. It's a bit like The Matrix. We have sense data that seems contiguous and continuous, and that's all we can really say about it.

Now, Anscombe wanted to challenge this worldview by claiming that 'blue' was still out there: that there was something 'blue' within an object that produced the sensory data we perceive as blueness. Wittgenstein introduced the quality 'painy' — the quality of being painful to touch — because it's quickly evident that a 'painy' surface does not itself contain pain. The sense data we label 'pain' is completely within the mind. We might say that a surface causes pain, but it makes no sense to say the surface contains pain or is pain. Once we recognize that, we also have to recognize that 'pain' and 'blue' are not different in kind; they are both mere sense data. Why would we say that 'blue' is contained within an object 'out there' when we are unwilling to say that 'pain' is in an object 'out there'? Stating that blue is 'out there' sets up a peculiar problematic that leads us to ask odd questions that carry us down the rabbit hole of philosophizing.