[Scientists] have learned to respect nothing but evidence, and to believe that their highest duty lies in submitting to it however it may jar against their inclinations.

I have never had the least sympathy with the a priori reasons against orthodoxy, and I have by nature and disposition the greatest possible antipathy to all the atheistic and infidel school. Nevertheless I know that I am, in spite of myself, exactly what the Christian would call, and, so far as I can see, is justified in calling, atheist and infidel.

The great thing in the world is not so much to seek happiness as to earn peace and self-respect.

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

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.

The only question which any wise man can ask himself, and which any honest man will ask himself, is whether a doctrine is true or false.

Time, whose tooth gnaws away everything else, is powerless against truth.