“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.”

First causes are outside the realm of science.

The great experimental principle, then, is doubt, that philosophic doubt which leaves to the mind its freedom and initiative, and from which the virtues most valuable to investigators in physiology and medicine are derived.

A great discovery is a fact whose appearance in science gives rise to shining ideas, whose light dispels many obscurities and shows us new paths.

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

Well-observed facts, though brought to light by passing theories, will never die; they are the material on which alone the house of science will at last be built.

Particular facts are never scientific; only generalization can establish science.

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.

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.

The mental never influences the physical. It is always the physical that modifies the mental, and when we think that the mind is diseased, it is always an illusion.

Science increases our power in proportion as it lowers our pride.

When we meet a fact which contradicts a prevailing theory, we must accept the fact and abandon the theory, even when the theory is supported by great names and generally accepted.

The terrain is everything; the germ is nothing.

The joy of discovery is certainly the liveliest that the mind of man can ever feel.

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

The better educated we are and the more acquired information we have, the better prepared shall we find our minds for making great and fruitful discoveries.

A man of science rises ever, in seeking truth; and if he never finds it in its wholeness, he discovers nevertheless very significant fragments; and these fragments of universal truth are precisely what constitutes science.

The human tongue is a beast that few can master.

It would not be impossible to prove with sufficient repetition and a psychological understanding of the people concerned that a square is in fact a circle. They are mere words, and words can be molded until they clothe ideas and disguise.

Such is the role of poetry. It unveils, in the strict sense of the word. It lays bare, under a light which shakes off torpor, the surprising things which surround us and which our senses record mechanically.

Sometimes it’s the words we choose not to say that speak most loudly about our character.

Every word is like an unnecessary stain on silence and nothingness.

As ideas are preserved and communicated by means of words, it necessarily follows that we cannot improve the language of any science, without at the same time improving the science itself; neither can we, on the other hand, improve a science without improving the language or nomenclature which belongs to it.

I hate the idea of always having to interpret other people’s ideas and thoughts and words, because I’m very independent and, I guess, a free thinker.

Be honest about what you can get. To make a sacrifice and to get what you want you need to be very certain. In other words: always think about your objective, have a clear goal and commit to it from the heart.