Shares with Bacon the title of Father of Modern Philosophy. All the
metaphysical writers follow him, as the men of the physical sciences
follow Bacon. He was only three and twenty when, whilst with his
regiment on the Danube, he determined to reform philosophy. To do so, he
resolved to efface from his mind all that he had learnt, and to admit
nothing that could not be demonstrated by reason and experience. With
him, consciousness was the sole _basis_, mathematics the sole _method_,
of certainty. He substituted the philosophy of reason for that of
authority. His genius for the great sciences, and his superiority over
the majority of his contemporaries in scientific acquirements, were
remarkable. He first applied algebra to geometry; he likewise made
observations on the decline of the magnetic needle, put forward the true
theory of the rainbow, and brought the science of optics within the
domain of mathematics. His influence over his age was great, though his
writings involved him in controversies. But he was timid as a man. He
wrote a book on astronomy, but destroyed it on learning the fate of
Galileo. He was the first great master of French prose. It is said of
him, that he began by doubting everything, and ended by believing that
he had left nothing unexplained.