All scientists know of colleagues whose minds are so well equipped with the means of refutation that no new idea has the temerity to seek admittance. Their contribution to science is accordingly very small.

Innocent, unbiased observation is a myth.

You have ... been told that science grows like an organism. You have been told that, if we today see further than our predecessors, it is only because we stand on their shoulders. But this [Nobel Prize Presentation] is an occasion on which I should prefer to remember, not the giants upon whose shoulders we stood, but the friends with whom we stood arm in arm ... colleagues in so much of my work.

Twice in my life I have spent two weary and scientifically profitless years seeking evidence to corroborate dearly loved hypotheses that later proved to be groundless; times such as these are hard for scientists-days of leaden gray skies bringing with them a miserable sense of oppression and inadequacy.

The intensity of a conviction that a hypothesis is true has no bearing on whether it is true or false. The importance of the strength of our conviction is only to provide a proportionately strong incentive to find out if the hypothesis will stand up to critical evaluation.

It goes with the passionate intensity and deep conviction of the truth of a religious belief, and of course of the importance of the superstitious observances that go with it, that we should want others to share it - and the only certain way to cause a religious belief to be held by everyone is to liquidate nonbelievers. The price in blood and tears that mankind generally has had to pay for the comfort and spiritual refreshment that religion has brought to a few has been too great to justify our entrusting moral accountancy to religious belief.

The alternative to thinking in evolutionary terms is not to think at all.