Spinoza's philosophy is deductive, rational, and monist. He shares with Descartes an intensely mathematical appreciation of the universe: Things make sense when understood in relation to a total structure; truth, like geometry, follows from first principles with a logic accessible and evident to man's mind. Whereas for Descartes mind and body are different substances, Spinoza holds that the two are different aspects of a single substance, which he called alternately God and Nature. Just as the mind is not substantially alien to the body, so Nature is not the product or agency of a supernatural God. The universe is a single substance, capable of an infinity of attributes, but known through two of them: physical "extension" and "thought." God is not the creator of a Nature beyond himself; God is Nature in its fullness.
Spinoza's rationalism, unlike that of later idealists, does not proceed at the expense of empirical observation. "Adequate ideas" are a coherent logical association of physical experiences. When ideas are confused or contradictory it is not because they are false (in the sense of contrary to fact) but because they are incomplete or improperly related to the totality of experience.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.