1596-1650. French mathematician and
philosopher. He believed that commonly
accepted knowledge was doubtful because of
the subjective nature of the senses, and
attempted to rebuild human knowledge using as
his foundation `cogito ergo sum' (`I think,
therefore I am'). He also believed that the
entire material universe could be explained
in terms of mathematical physics. He is
regarded as the discoverer of analytical
geometry and the founder of the science of
optics, and also helped to shape contemporary
theories of astronomy and animal behaviour.
Born near Tours, Descartes served in the army
of Prince Maurice of Orange, and in 1619,
while travelling through Europe, decided to
apply the methods of mathematics to
metaphysics and science. He settled in the
Netherlands in 1628, where he was more likely
to be free from interference by the
ecclesiastical authorities. In 1649 he
visited the court of Queen Christina of
Sweden, and shortly thereafter he died in
Stockholm. His works include Discourse on
Method 1637, Meditations on the First
Philosophy 1641, and Principles of Philosophy
1644, and numerous books on physiology,
optics, and geometry. Coordinate geometry, as
a way of defining and manipulating
geometrical shapes by means of algebraic
expressions, was determined by Leibniz, and
only later called Cartesian coordinates in
honour of Descartes. Descartes identified the
`thinking thing' (res cogitans) or mind with
the human soul or consciousness; the body,
though somehow interacting with the soul, was
a physical machine, secondary to, and in
principle separable from, the soul. He held
that everything has a cause; nothing can
result from nothing. He believed that,
although all matter is in motion, matter does
not move of its own accord; the initial
impulse comes from God. He also postulated
two quite distinct substances - spatial
substance, or matter, and thinking substance,
or mind. This is called `Cartesian dualism',
and it preserved him from serious controversy
with the church.