The article defines and juxtaposes relationist and system approaches to the phenomenon of the power. Relationist concept/s («power over smth.») consider power and power relations as a possibility for an individual / group to change the behavior of another individual or group. In the system approach, or a concept of «power for smth.», power is defined as a specific impersonal quality of political system, as an internal functional, not joined with an individual or group of individuals. The authors put some considerations on the possible advantages of the system approach to power as applied to Medieval and Early modem studies. Key elements of the conceptual scheme proposed by the authors are the following: 1) power as substantial phenomenon; 2) pro-power discourse; 3) contra-power discourse; 4) power practices, generalizing original discourses, in other words, power as process.