Reason and judgment are the qualities of a leader.

It belongs to human nature to hate those you have injured.

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

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

Perhaps the most valuable result of all education is the ability to make yourself do the thing you have to do, when it ought to be done, whether you like it or not it is the first lesson that ought to be learned and however early a man’s training begins, it is probably the last lesson that he learns thoroughly.

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

The great end of life is not knowledge but action.

Sit down before fact like a little child, and be prepared to give up every preconceived notion. Follow humbly wherever and to whatever abyss Nature leads, or you shall learn nothing.

The chess board is the world, the pieces are the phenomena of the universe, the rules of the game are what we call the laws of Nature. The player on the other side is hidden from us. We know that his play is always fair, just, and patient. But we also know, to our cost, that he never overlooks a mistake, or makes the smallest allowance for ignorance.

Irrationally held truths may be more harmful than reasoned errors.

Science is nothing but trained and organized common sense.

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

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

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

It is an error to imagine that evolution signifies a constant tendency to increased perfection. That process undoubtedly involves a constant remodelling of the organism in adaptation to new conditions but it depends on the nature of those conditions whether the directions of the modifications effected shall be upward or downward.

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

Perhaps the most valuable result of all education is the ability to make yourself do the thing you have to do, when it ought to be done, whether you like it or not.

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

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