Rationalism — An epistemological tradition holding that reason is the primary source of genuine knowledge, maintaining that at least some fundamental truths about reality can be reached by the intellect independently of sense experience. The term derives from the Latin ratio (“reason,” “calculation”). In its classic form it is associated with the great Continental systems of the seventeenth and early eighteenth centuries. In the Meditations, Descartes seeks an indubitable foundation in the cogito and holds that innate ideas — such as those of God, extension, and thought — are known with more clarity and distinctness than any data of the always fallible senses. In the Ethics, Spinoza pushes this impulse to its limit by laying out the whole of reality more geometrico, that is, deduced from definitions and axioms as in a geometrical treatise. Leibniz distinguishes truths of reason, which are necessary and grounded in the principle of non-contradiction, from truths of fact, which are contingent and governed by the principle of sufficient reason. The paradigmatic example of rationalist knowledge is mathematics: that the angles of a triangle sum to a constant is discovered not by measuring triangles but by demonstration from principles. Rationalism is opposed to empiricism, for which all knowledge ultimately derives from experience — a contrast that structures much of modern epistemology. Kant would seek to overcome this opposition by showing how a priori knowledge and sensory data cooperate in constituting experience.
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