A discovery is generally an unforeseen relation not included in theory.

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

We must never make experiments to confirm our ideas, but simply to control them.

We must keep our freedom of mind, ... and must believe that in nature what is absurd, according to our theories, is not always impossible.

Theories are like a stairway; by climbing, science widens its horizon more and more, because theories embody and necessarily include proportionately more facts as they advance.

Science does not permit exceptions.

In every enterprise ... the mind is always reasoning, and, even when we seem to act without a motive, an instinctive logic still directs the mind. Only we are not aware of it, because we begin by reasoning before we know or say that we are reasoning, just as we begin by speaking before we observe that we are speaking, and just as we begin by seeing and hearing before we know what we see or what we hear.