e of abode
(1629), and though often shifting his residence, little disturbed
save by the controversies of philosophy and the orthodox zeal of Dutch
theologians, he gave his best hours during twenty years to thought.
An invitation from Queen Christina to the Swedish court was accepted
in 1649. The change in his habits and the severity of a northern winter
proved fatal to the health which Descartes had carefully cherished;
in February of 1650 he was dead.

The mathematical cycle in the development of Descartes' system of
thought preceded the metaphysical. His great achievements in
analytical geometry, in optics, in physical research, his
explanation of the laws of nature, and their application in his theory
of the material universe, belong to the history of science. Algebra
and geometry led him towards his method in metaphysical speculation.
How do all primary truths verify themselves to the human mind? By
the fact that an object is clearly and distinctly conceived. The
objects of knowledge fall into certain groups or series; in each
series there is some simple and dominant element which may be
immediately apprehended, and in relation to which the subordinate
elements become intelligible. Let us accept nothing on hearsay or
authority; let us start with doubt in order to arrive at certitude;
let us test the criterion of certitude to the uttermost. There is
one fact which I cannot doubt, even in doubting all--I think, and
if I think, I exist--"Je pense, donc je suis." No other evidence of
this is needed than that our conception is clear and distinct; in
this clearness and distinctness we find the principle of certitude.
Mind, then, exists, and is known to us as a thinking substance. But
the idea of an infinite, perfect Being is also present to our
intellect; we, finite, imperfect beings, could not have made it;
unmake it we cannot; and in the conception of perfection that of
existence is involved. Therefore God exists, and therefore the laws
of our consciousness, which are His laws, cannot deceive us. We have
seen what mind or spirit signifies--a thinking substance. Reduce our
idea of matter to clearness and distinctness, and what do we find?
The idea of an extended substance. Our complex humanity, made up of
soul and body, comprises both kinds of substance. But thought and
extension have nothing in common; their union can only be conceived
as the collocation at a single point of a machine with that which
raises it above