The Moorean Shift

G.E. Moore

If I don't know* I'm dreaming, then I don't know if I'm standing up.

Skeptic:
I don't know I'm dreaming.
Therefore, I don't know if I'm standing up

Moorean Shift:
I know that I'm standing up.
Therefore, I know that I'm not dreaming.

"I agree, therefore, with that part of the argument which asserts that if I don't know that I'm not dreaming, it follows that I don't know that I'm standing up, even if I both actually am and think that I am. But this first part of the argument is a consideration which cuts both ways. For, if it is true, it follows that it is also true that if I do know that I am standing up, it follows that I do know that I'm not dreaming. I can therefore just as well argue: since I do know that I'm standing up, it follows that I do know that I'm not dreaming; as my opponent can argue: since you don't that you're not dreaming, it follows that you don't know that you're standing up. The one argument is just as good as the other, unless my opponent can give better reasons for asserting that I don't know that I'm not dreaming, than I can give for asserting that I do know that I'm standing up."  (Moore, G.E. 1959. Philosophical Papers. p. 247)

* "to know" for Moore  is synonymous with "to be certain"