It is wrong for a man to say that he is certain of the objective truth of any proposition unless he can produce evidence which logically justifies that certainty.

It is not what we believe, but why we believe it. Moral responsibility lies in diligently weighing the evidence. We must actively doubt; we have to scrutinize our views, not take them on trust. No virtue attached to blindly accepting orthodoxy, however 'venerable'.

A well-worn adage advises those who set out upon a great enterprise to count the cost, yet some of the greatest enterprises have succeeded because the people who undertook them did not count the cost.

A man who speaks out honestly and fearlessly that which he knows, and that which he believes, will always enlist the good will and the respect, however much he may fail in winning the assent, of his fellow men.

Science is simply common sense at its best, that is, rigidly accurate in observation, and merciless to fallacy in logic.

Of moral purpose I see no trace in Nature. That is an article of exclusively human manufacture and very much to our credit.

It is better to read a little and thoroughly than cram a crude undigested mass into my head, though it be great in quantity.