1. any philosophical position holding that (a) it is possible to obtain knowledge of reality by reason alone, unsupported by experience, and (b) all human knowledge can be brought into a single deductive system. This confidence in reason is central to classical Greek philosophy, notably in its mistrust of sensory experience as a source of truth and the preeminent role it gives to reason in epistemology. However, the term rationalist is chiefly applied to thinkers in the Continental philosophical tradition initiated by René Descartes, most notably Baruch Spinoza and Gottfried Wilhelm Leibniz. Rationalism is usually contrasted with empiricism, which holds that knowledge comes from or must be validated by sensory experience. Psychoanalytical approaches, humanistic psychology, and some strains of cognitive theory are heavily influenced by rationalism.

2. in religion, a perspective that rejects the possibility or the viability of divine revelation as a source of knowledge.

3. in general, any position that relies on reason and evidence rather than on faith, intuition, custom, prejudice, or other sources of conviction. —rationalist adj., n.