Not far from the invention of fire we must rank the invention of doubt.

Skepticism is the highest duty and blind faith the one unpardonable sin.

Oh devil! truth is better than much profit. I have searched over the grounds of my belief, and if wife and child and name and fame were all to be lost to me one after the other as the penalty, still I will not lie.

The great thing in the world is not so much to seek happiness as to earn peace and self-respect.

My experience of the world is that things left to themselves don't get right.

The dogma of the infallibility of the Bible is no more self-evident than is that of the infallibility of the popes.

Regarded anatomically, the resemblances between the foot of Man and the foot of the Gorilla are far more striking and important than the differences... be the differences between the hand and foot of Man and those of the Gorilla what they may the differences between those of the Gorilla and those of the lower Apes are much greater.