Henri Poincaré

The only objective reality is the one that is common to several thinking beings.

The geometer is not a man of the world, but a man of the world of ideas.

The true method is to begin by doubting, and to end by believing.

Absolute space, absolute time, and absolute simultaneity are not concepts that can be derived from experience.

The continuum is not given to us by intuition, but constructed by the mind.

The physicist's task is to predict.

Experience is the sole source of truth.

The harmony of the world is revealed in the laws of nature.

The mathematical sciences particularly exhibit order, symmetry, and limitation; and these are the greatest forms of the beautiful.

The role of mathematics is to make the invisible visible.

The mind can only understand what it has itself constructed.

The most fruitful discoveries are those which reveal to us a new analogy.

The true reality is the one that is independent of our senses.

The scientist must be a poet in his heart and a logician in his head.

The only way to learn mathematics is to do mathematics.

The value of a scientific theory is measured by its predictive power.

The laws of nature are not arbitrary, but necessary.

The universe is a machine for making gods.

The human mind is not a passive recipient of knowledge, but an active constructor of it.

The most beautiful theories are those which are simple and elegant.