One geometry cannot be more true than another; it can only be more convenient.

For a long time the objects that mathematicians dealt with were mostly ill-defined; one believed one knew them, but one represented them with the senses and imagination; but one had but a rough picture and not a precise idea on which reasoning could take hold.

Astronomy is useful because it raises us above ourselves; it is useful because it is grand; .... It shows us how small is man's body, how great his mind, since his intelligence can embrace the whole of this dazzling immensity, where his body is only an obscure point, and enjoy its silent harmony.

One does not ask whether a scientific theory is true, but only whether it is convenient.

Just as houses are made of stones, so is science made of facts.

It is the simple hypotheses of which one must be most wary; because these are the ones that have the most chances of passing unnoticed.

Geometry is the art of correct reasoning from incorrectly drawn figures.