Responding to an argument for skepticism:

That is to say, though, as I have said, I agree with Russell that (1), (2), and (3) are true; yet of no one even of these three do I feel as certain as that I do know for certain that this is a pencil. Nay more: I do not think it is rational to be as certain of any one of these four propositions, as of the proposition that I do know that this is a pencil.

- G.E. Moore, quote found here.