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

The true worth of an experimenter consists in his pursuing not only what he seeks in his experiment, but also what he did not seek.

It has often been said that, to make discoveries, one must be ignorant. This opinion, mistaken in itself, nevertheless conceals a truth. It means that it is better to know nothing than to keep in mind fixed ideas based on theories whose confirmation we constantly seek, neglecting meanwhile everything that fails to agree with them.

Men who believe too firmly in their theories, do not believe enough in the theories of others. So ... these despisers of their fellows ... make experiments only to destroy a theory, instead of to seek the truth.

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

We must remain, in a word, in an intellectual disposition which seems paradoxical, but which, in my opinion, represents the true mind of the investigator. We must have a robust faith and yet not believe.

Science does not permit exceptions.