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

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.

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.

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

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

The world makes up for all its follies and injustices by being damnably sentimental.

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.

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 comits suicide when it adopts a creed.

Science is nothing but trained and organized common sense, differing from the latter only as a veteran may differ from a raw recruit: and its methods differ from those of common sense only as far as the guardsman's cut and thrust differ from the manner in which a savage wields his club.

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

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

It is not who is right, but what is right, that is of importance.

I have no faith, very little hope, and as much charity as I can afford.

Try to learn something about everything and everything about something.

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

Only a scientific people can survive in a scientific future.

Sit down before fact as a little child, be prepared to give up every preconceived notion... or you shall learn nothing.

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.

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

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

Irrationally held truths may be more harmful than reasoned errors.

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.