Rationalism [Ratsionalizm] was a modernist movement in Soviet architecture that was current in the 1920s and early 1930s. It was led by the architect and prominent architectural pedagogue Nikolai Aleksandrovich Ladovskii (1881–1941). Constructivism and Rationalism were the two major rival approaches to architectural Modernism in the USSR. Whereas Ladovskii referred to his method as “rationalist architecture” or “ratio-architecture” [ratsionalisticheskaiaarkhitektura; ratsio-arkhitektura], the constructivists derogatively called Ladovskii’s school “Formalism.” The ethnically natural term “Rationalism” was introduced by the historian Selim Khan-Magomedov in the 1960s.