Who never doubted never half believed. Where doubt is there truth is - it is her shadow.

Beyond a doubt truth bears the same relation to falsehood as light to darkness.

Doubt indulged and cherished is in danger of becoming denial but if honest and bent on thorough investigation it may soon lead to full establishment of the truth.

When in doubt tell the truth.

If you would be a real seeker after truth it is necessary that at least once in your life you doubt as far as possible all things.

Truth is beautiful without doubt but so are lies.

Our authorities leave us no doubt that the trust lodged with the oligarchy was sometimes abused but it certainly ought not to be regarded as a mere usurpation or engine of tyranny.

Better to trust the man who is frequently in error than the one who is never in doubt.

In your hands or that of any other person so much power would no doubt be dangerous. I am the only man in the world whom it would be safe to trust with it. Remember I am a prophet!

I know it when I don't know it. Sometimes I know it when I don't think I know it. I need to trust myself in these moments these rare moments of self-doubt.