Wittgenstein denies the Cartesian-esque theses that we undergo private expriences, that the mind is somewhat like an inner theatre of experience. But this view seems to have much going for it.
For example, it seems intuitive that when I remember something, there is an inner process taking place to which I affix the term “remember.” And what I mean by “remember” is just what this inner process is. But Wittgenstein thinks this intuition mistaken. Consider an example: Suppose I (qua a Cartesian soul) decide to take note of a certain sensation I experience by recording “S” in a diary whenever I have this experience. I say that by “S” I mean this sensation, but just how is this relationship established? What is it precisely that affixes “S” to this particular sensation? One cannot just ostensibly define a sign unto himself.
Nevertheless, when I remember, there seems to be a certain mental object, something there that I (and only I) “see.” And it is for this mental process that I use the word “remember.” But Wittgenstein insists that it is a mistake to think that “the picture of the inner process gives us the correct idea of the use of the word ‘to remember.'” It is not possible to translate a private experience into a public language. But this is not to deny that there is a mental process of remembering, he says (this would be nothing other than behaviorism). Rather to speak of a mental process of remembering is nothing other than that the individual has remembered.
Maybe it’s just me, but I find this ambiguous in the Phil. Investigations: Does Wittgenstein mean to deny the possibility of private experience because they couldn’t be expressed in natural language, or does he mean to say that even if private experiences were possible, we couldn’t express them in natural language? He could have intended the latter. In that case, he would admit that private experiences were possible but that we just couldn’t express them .
I think one putative example of this would be qualia–the thesis that for some sentient organism there is in all its consciousness and sensory perceptions, a certain subjectivity such that there is something it is like for that organism to be conscious or to have a sensation. There is something it is like for me to see this piece of paper that I have here before me–and what that is, is something that I am immediately acquainted with. And this, further, is an irreducibly mental object. Indeed it is a private mental object. No one knows what it is like for me to see this piece of paper but me. But qualia are thought to be inexpressible. I do not know how I could, in any natural languge, express what it is like for me to see the color green. So qualia sensations are at least one putative example of private experiences.