Henri Poincaré

Experiment is the sole source of truth.

The aim of science is not things but the relations between things.

Logic may direct and discipline intuition, but it cannot originate it.

A scientist worthy of his name, about all a mathematician, experiences in his work the same impression the artist has in creating a work of art.

It is far better to foresee even without certainty than not to foresee at all.

The mathematical facts worthy of our notice are those which teach us something new.

Doubt is the origin of wisdom.

The universe is like a safe to which there is a combination, but the combination is lost.

Invention consists in avoiding the fixations of old habits.

The sterile discussion of the nature of mathematics is like the futile discussion of whether chess is a science or an art.

Life is a perpetual education.

To know, is to know that one knows; to know that one does not know, is to know.

The greatest pleasure in life is doing what people say you cannot do.

Science is facts; just as houses are made of stones, so is science made of facts; but a pile of stones is not a house and a collection of facts is not necessarily science.

Absolute space, that is to say, the view of space which is independent of its contents, withdraws from the laws of nature.

The mind has its own laws, and it is by these that we must be guided.

What then is a mathematical discovery? It is rather an invention of the human mind.

It is often the case with theories that they begin as hypotheses and end as facts.

The role of the infinitely small in nature is infinitely large.

Thought is only a flash between two long nights; but this flash is everything.