Unity of plan everywhere lies hidden under the mask: of diversity of structure-the complex is everywhere evolved out of the simple.

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

The mathematician starts with a few propositions, the proof of which is so obvious that they are called self-evident, and the rest of his work consists of subtle deductions from them. The teaching of languages, at any rate as ordinarily practiced, is of the same general nature authority and tradition furnish the data, and the mental operations are deductive.

The man of science has learned to believe in justification, not by faith, but by verification.

Skepticism is the highest duty and blind faith the one unpardonable sin.

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'.

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