rationalism [Lat., = belonging to reason], in philosophy, a theory that holds that reason alone, unaided by experience, can arrive at basic truth regarding the world. Associated with rationalism is the doctrine of innate ideas and the method of logically deducing truths about the world from "self-evident" premises. Rationalism is opposed to empiricism on the question of the source of knowledge and the techniques for verification of knowledge. René Descartes, G. W. von Leibniz, and Baruch Spinoza all represent the rationalist position, and John Locke the empirical. Immanuel Kant in his critical philosophy attempted a synthesis of these two positions. More loosely, rationalism may signify confidence in the intelligible, orderly character of the world and in the mind's ability to discern such order. It is opposed by irrationalism, a view that either denies meaning and coherence in reality or discredits the ability of reason to discern such coherence. Irrational philosophies accordingly stress the will at the expense of reason, as exemplified in the existentialism of Jean-Paul Sartre or Karl Jaspers. In religion, rationalism is the view that recognizes as true only that content of faith that can be made to appeal to reason. In the Middle Ages the relationship of faith to reason was a fundamental concern of scholasticism. In the 18th cent. rationalism produced a religion of its own called deism (see deists).
See E. Heimann, Reason and Faith in Modern Society (1961); T. F. Torrance, God and Rationality (1971); R. L. Arrington, Rationalism, Realism, and Relativism (1989).