The article offers definitions of the social development subject in social epistemology, in the sociocultural analysis of Russia’s social dynamics, in the concept of economic sociodynamics, in the idea of the multidimensionality of social mobility, in the concept of “release” of management from the power of syncresis “power-management-property”, in the social managerial concept of subjectivity issues. An analysis of the subjectivity of development through the interconnection of the concepts: “subject of social development” and “mediation” is argued for. Two sides of the mediation process are emphasized: a destructive one, which occurs when the subject, beginning a transition from the old to the new, was unable to complete it, and creative one, when the transition ends with the formation of a third meaning as an alternative to the original meanings.