This article examines the role of M.G. Yaroshevsky in advancing the study of conceptual foundations in psychological science. The purpose of this research was to elucidate Yaroshevsky's views on the problem of psychological categories and their historical and methodological significance. The study employed comparative-historical and bibliographic methods, alongside categorical analysis. It is argued that the scholar considered a structured system of categories to be the foundation of a research program. The analysis demonstrates that he deemed it essential to distinguish between the invariant and variable conceptual content of psychology. Yaroshevsky proposed the categorical approach as a promising direction for the history and methodology of psychology. Furthermore, he identified three types of reductionism within psychological science: disciplinary (reducing psychological concepts to biological or sociological ones), categorical (attempting to reduce all psychological concepts to a single category), and level-based (reducing complex mental phenomena to elementary components). Through historical-psychological research, Yaroshevsky documented instances of categorical reductionism in attempts to construct conceptual systems for psychoanalysis, behaviorism, Gestalt psychology, role theory, and existential psychology. In light of these unsuccessful attempts, he—together with A.V. Petrovsky and V.A. Petrovsky—proposed two versions of a categorical system for psychology (in 1999 and 2003), comprising 24 and 35 concepts, respectively. In conclusion, the large-scale, three-decade development of the problem of psychological concepts undertaken by M.G. Yaroshevsky establishes him as one of the foremost Russian scholars in this field, contributing significantly during both the Soviet and post-Soviet periods of Russian psychology.