Doubt is the vestibule through which all must pass before they can enter into the temple of wisdom.

The greatest obstacle to being heroic is the doubt whether one may not be going to prove one's self a fool the truest heroism is to resist the doubt and the profoundest wisdom to know when it ought to be resisted and when it be obeyed.

I have no doubt that we will be successful in harnessing the sun's energy. If sunbeams were weapons of war we would have had solar energy centuries ago.

There's no doubt that usually a president's public image is enhanced by going to war. That never did appeal to me.

To walk through the ruined cities of Germany is to feel an actual doubt about the continuity of civilization.

I put forward formless and unresolved notions as do those who publish doubtful questions to debate in the schools not to establish the truth but to seek it.

Any truth is better than indefinite doubt.

It is by doubting that we come to investigate and by investigating that we recognize the truth.

The key to wisdom is this - constant and frequent questioning for by doubting we are led to question and by questioning we arrive at the truth.

Believe those who are seeking the truth. Doubt those who find it.