Make up your mind to act decidedly and take the consequences. No good is ever done in this world by hesitation.

The great end of life is not knowledge but action.

Agnosticism simply means that a man shall not say he knows or believes that for which he has no grounds for professing to believe.

A man's worst difficulties begin when he is able to do as he likes.

If a little knowledge is dangerous, where is the man who has so much as to be out of danger?

Sit down before fact as a little child, be prepared to give up every preconceived notion, follow humbly wherever and whatever abysses nature leads, or you will learn nothing.

I am too much of a skeptic to deny the possibility of anything.

It is the customary fate of new truths to begin as heresies and end as superstitions.

Time, whose tooth gnaws away everything else, is powerless against truth.

For every man the world is as fresh as it was at the first day, and as full of untold novelties for him who has the eyes to see them.