Men can intoxicate themselves with ideas as effectually as with alcohol or with bang and produce, be dint of serious thinking, mental conditions hardly distinguishable from monomania.

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'.

Misery is a match that never goes out.

[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 protest that if some great Power would agree to make me always think what is true and do what is right, on condition of being turned into a sort of clock and would up every morning before I got out of bed, I should instantly close with the offer.

If a man cannot do brain work without stimulants of any kind, he had better turn to hand work it is an indication on Nature's part that she did not mean him to be a head worker.

The only people, scientific or other, who never make mistakes are those who do nothing.