On Certainty.

"It is not true that a mistake merely gets more and more improbable as we pass from [knowing about] the planet to my own hand. No: at some point it has ceased to be conceivable. This is already suggested by the following: if it were not so, it would also be conceivable that we should be wrong in every statement about physical objects; that any we ever make are mistaken.// So is the hypothesis possible, that all the things around us don't exist? Would that not be like the hypothesis of our having miscalculated all our calculations?" - Ludwig Wittgenstein, On Certainty, §54-55

This makes it look as though the skeptic is really asking:

"Is it possible, right now, that I am not speaking a language? (That my words do not refer.)"

Or, we can connect it with Heidegger's assertion in Being and Time that the skeptic is in the grip of suicide: The skeptic doubts, e.g. that there is such a thing as "calculating," distinct from "miscalculating." He doubts the practices the he must engage in to live his life.

With the skeptic's questions, the wheels come off the cart. If we accept the skeptic's doubts, then we have no valid criteria of meaning. But that would mean that our own words and actions are non-sensical. Does this show that his worries are unfounded? After all, isn't this precisely what he is worried about?

But then we might wonder with Wittgenstein: what is the source of the skeptic's worry? Should we treat it as a philosophical doubt or is his concern based in a psychological disturbance? (i.e. Is there a reason behind the skeptic's question or only a cause?) Is the skeptic's concern really knowledge or is he discontent with the state of affairs more generally? (He doubt is a manifestation of his estrangement from his own language and actions.)