This paper explores the composition logic of the creativity of the Avant-garde masters and to identify the principles of the composition language of the architecture of modernism.To characterize the composition language of Avant-garde architecture, systemic, historical-genetic and semiotic methods of research are used. Architectural composition is interpreted as an activity that has its own semantic, morphological and syntactic features. In the example of Svoboda Square (the former Dzerzhinsky Square) in Kharkiv, the logical methods of artistic activity and thinking of the architects of the Soviet Avant-garde of the 1920-1930s are studied.At the beginning of the 20th century avant-garde movements were created artificially, consciously, by an act of will, and they strove to dictate their ideas, concepts and principles as universal and general. The architectural language of the Avant-garde is normative, ascetic and rigidly organized. Distinctive features of the artistic movements of the Avant-garde are the deep analyticity of thinking and the normativity of the declared requirements, abstract concepts and symbols. The logical principles of composition are often repeated thanks to stable semantic associations and are reflected in geometric structures and forms. Thus, the methods of compositional thinking of the Avant-garde form a monological system, i.e. they are internally holistic and normative, not allowing alternatives. It was possible to identify and show that the Avant-garde, as a monological language system, is characterized by the following features: internal integrity, self-sufficiency, normativity; stability of figurative language devices; restriction of freedom of artistic expression with the help of a concept, declaration, slogan, clear conceptual system.Researchers and designers should treat the phenomenon under study not as a “closed”, stylistically defined object, but see it as a complex historical process of structure formation based on an even more complex process of development of thinking and activity of architects and builders of a particular period.