The science of life is a superb and dazzlingly lighted hall which may be reached only by passing through a long and ghastly kitchen.

The experimenter who does not know what he is looking for will not understand what he finds.

The investigator should have a robust faith - and yet not believe.

A fact in itself is nothing. It is valuable only for the idea attached to it, or for the proof which it furnishes.

Progress is achieved by exchanging our theories for new ones which go further than the old, until we find one based on a larger number of facts. ... Theories are only hypotheses, verified by more or less numerous facts. Those verified by the most facts are the best, but even then they are never final, never to be absolutely believed.

But while I accept specialization in the practice, I reject it utterly in the theory of science.

Men who have excessive faith in their theories or ideas are not only ill prepared for making discoveries; they also make very poor observations. Of necessity, they observe with a preconceived idea, and when they devise an experiment, they can see, in its results,only a confirmation of their theory. In this way they distort observation and often neglect very important facts because they do not further their aim.