Rationalism- The intellectual principles of Rationalism are based on architectural theory. Vitruvius had already established in his work De Architectura that architecture is a science that can be comprehended rationally. This formulation was taken up and further developed in the architectural treatises of the Renaissance. Progressive art theory of the 18th-century opposed the Baroque beauty of illusionism with the classic beauty of truth and reason.
Twentieth-century Rationalism derived less from a special, unified theoretical work than from a common belief that the most varied problems posed by the real world could be resolved by reason. In that respect it represented a reaction to historicism and a contrast to Art Nouveau and Expressionism.
Source- Wikipedia