The importance of involving new methodological instruments in legal science (in terms of abandoning the prevalence of legal normativism and the proclamation of ideological pluralism) has stipulated the urgency of the research. The aim of the study is to focus the scholars’ attention on the importance of involving into jurisprudence the activity-based theory as a means of interpreting legal phenomena and processes and determining the boundaries and principles of its application. It is noted that quite often domestic scientists while conducting research draw attention to the use of the activity based approach, although they do not reveal its epistemological potential in detail. The connection of the boundaries of the use of the methodological approach in general and the activity based approach, in particular, with the issue of principles of the appropriate approach application (because the principles determine the possible ways of the fundamental provisions of a particular theory use, and its limits) is emphasized. Propaedeutic provisions on the limits and principles of the activity based approach are the issues of distinguishing between scientific and non-scientific knowledge. Karl Popper’s concept of forming a system of new knowledge in terms of requirements for new scientific theory is elucidated. It is pointed out that the activity based theory as an epistemological component of legal science also has its cognitive boundaries: it cannot be used to explain absolutely all phenomena and processes in the field of law. The factors of the activity based theory application limits are binary: on the one hand – it is the very nature of scientific knowledge determining the object of epistemology; on the other hand, it is the nature of the activity itself that limits the effectiveness of the use of the provisions of activity based theory to dynamic phenomena and processes in the field of law. The importance of two principles of the activity based theory application (except for the general scientific principles of objectivity; comprehensiveness and completeness): the principle of the subject and the situational and action principle is emphasized. The first of them is related to the fact that a person with inherent dignity and rights is the main subject of law in a civilized society. The principle of the subject directs to the interpretation of the content of the subject-subject interaction, to the essential characteristics of the subject, and etc. The second principle determines the need to consider the conditions for the implementation of legal provisions, specific life circumstances, subjective elements of the person’s activity. It is concluded that the scientific justification for the involvement of the activity based theory in jurisprudence involves clarifying the possibility of separating scientific knowledge resulting from the use of this theory from non- scientific and determining the boundaries and principles of applying the provisions and conclusions of the theory to interpret legal phenomena and processes. In this case, the theory of activity itself can be a test theory (by Karl Popper’s terminology) or a critique of the test theory (bearing in mind the communicative theory of law). Key words: scientific theory, methodology, jurisprudence, subject principle, theory of activity.