Only one absolute certainty is possible to man, namely that at any given moment the feeling which he has exists.

Science is nothing but trained and organized common sense.

Science ... warns me to be careful how I adopt a view which jumps with my preconceptions, and to require stronger evidence for such belief than for one to which I was previously hostile. My business is to teach my aspirations to conform themselves to fact, not to try and make facts harmonize with my aspirations.

The great end of life is not knowledge but action.

There is no greater mistake than the hasty conclusion that opinions are worthless because they are badly argued.

Every great advance in natural knowledge has involved the absolute rejection of authority.

The great tragedy of science -- the slaying of a beautiful hypothesis by an ugly fact.

The strongest man in the world is the man who stands alone.

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

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

Try to learn something about everything and everything about something.

Irrationally held truths may be more harmful than reasoned errors.

God give me strength to face a fact though it slay me.

The deepest sin against the human mind is to believe things without evidence.

Thoughtfulness for others, generosity, modesty, and self-respect are the qualities which make a real gentleman or lady.

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