1 Philos. the theory that reason is the foundation of certainty in knowledge (opp. EMPIRICISM (see EMPIRIC), SENSATIONALISM).
2 Theol. the practice of treating reason as the ultimate authority in religion.
3 a belief in reason rather than religion as a guiding principle in life.
Derivatives:
rationalist n. rationalistic adj. rationalistically adv.
Useful english dictionary. 2012.