Believe those who are seeking the truth; doubt those who find it - André Gide
For men become civilized, not in proportion to their willingness to believe, but in their readiness to doubt - Henry Louis Mencken
Give me the benefit of your convictions, if you have any, but keep your doubts to yourself, for I have enough of my own - Johann Wolfgang von Goethe
Fanatic orthodoxy is never rooted in faith but in doubt. It is when we are not sure that we are doubly sure - Reinhold Niebuhr
If there were no falsehood in the world, there would be no doubt; if there were no doubt, there would be no inquiry; if no inquiry, no wisdom, no knowledge, no genius - Walter Savage Landor
When in doubt wear red - Bill Blass
