Can you disbelieve in something you don't know about? […] It isn't that I don't believe but that I don't know.

In order to determine whether we can know anything with certainty, we first have to doubt everything we know

To believe that we know nothing assuredly, and cannot ever know anything assuredly, is to take too much on faith.

To doubt everything or to believe everything are two equally convenient solutions; both dispense with the necessity of reflection. (Note: This quote, although found in the 1985 sci-fi novel, 'Lucifer's Hammer', by Larry Niven and Jerry Pournelle, may be erroneously attributed to Pournelle. As this quote can also be found in the Preface of Henri Poincare's "Science and Hypothesis" the 1952 Dover abridged edition)

If man of himself could in a perfect manner know all things visible and invisible, it would indeed be foolish to believe what he does not see. But our manner of knowing is so weak that no philosopher could perfectly investigate the nature of even one little fly.

115. If you tried to doubt everything you would not get as far as doubting anything. The game of doubting itself presupposes .

Don't believe everything you think.

I believe that we do not know anything for certain, but everything probably.