Extinguished theologians lie about the cradle of every science, as strangled snakes beside that of Hercules

And when you cannot prove that people are wrong, but only that they are absurd, the best course is to let them alone.

I am content with nothing, restless and ambitious... and I despise myself for the vanity, which formed half the stimulus to my exertions. Oh would that I were one of those plodding wise fools who having once set their hand to the plough go on nothing doubting.

Learn what is true in order to do what is right.

The supernatural is being swept out of the universe in the flood of new knowledge of what is natural. It will soon be as impossible for an intelligent, educated man or woman to believe in a god as it is now to believe that earth is flat, that flies can be spontaneously generated, that disease is a divine punishment, or that death is always due to witchcraft.

People never will recollect that mere learning and mere cleverness are of next to no value in life, while energy and intellectual grip, the things that are inborn and cannot be taught, are everything.

In matters of the intellect, do not pretend that conclusions are certain which are not demonstrated or demonstrable. That I take to be the agnostic faith, which if a man keep whole and undefiled, he shall not be ashamed to look the universe in the face, whatever the future may have in store for him.