Spinoza is the only Jewish thinker among the rationalists. He was excommunicated from the Jewish community of Amsterdam, possibly on account of the heretical views that he held about the nature of God and the immortality of the soul, views later elaborated in his great systematic work, the Ethics. Spinoza's philosophical system is the purest example of rationalism.
Other rationalists remained committed to the truths of revealed religion; Spinoza maintains that the Bible does not contain the word of God, but is a work of men that serves the sociopolitical ends of establishing and securing the commonwealth. In his Theological-Political Treatise, Spinoza therefore argues that human beings should be free to hold whatever religious views they like, provided they do not upset the established civil order.
This work is a prolegomenon to the Ethics, where, on the basis of reason alone, Spinoza radically reconfigures traditional notions of God, nature, and morality. Rejecting all sensory inputs as mere "random experience" that do not reveal the nature of the world, he says there is only one substance, which he strikingly calls "God or nature." All existing things must be understood to be merely modifications of that single substance, not substances in their own right. One of the most provocative aspects of Spinoza's vision of the universe, which drew sustained criticism from his contemporaries, is his claim that all events are determined by God to occur. Indeed, he maintains, even God does not freely choose to create the world—this in sharp contrast to traditional views of God as creator—but is determined by his own nature to produce what exists in the world. This determinism renders the structure of nature intelligible to the human intellect.
By understanding the necessary and eternal order of the world, humans may come to understand both their place in the world and what they ought to do in the world. By achieving this understanding, they may achieve a kind of nontheological immortality. Their reason, which grasps the unchanging and eternal order of nature, enables them to achieve a kind of immortality as well.
Science EncyclopediaScience & Philosophy: Quantum electronics to ReasoningRationalism - Rationalism Defined, The Roots Of Rationalism, René Descartes, Benedict Spinoza, Nicolás Malebranche, Gottfried Wilhelm Von Leibniz