The author states that once upon a time Russian structures of power were similar to those in Western Europe and - consequently - he focuses on their terminology in Russian sources since the fourteenth century. He concentrates on political and legal system as well as political and social changes in Rus and widely presents terms and concepts, which were used in the historical sources to describe these phenomena. He also tries to explain the genealogical terminology of agnatic seniority, which regulated relations between Russian dukes. There was a hierarchy of 'brotherhood' that distinguished between 'older' and 'younger' brothers within the group of dukes, what brought serious political and legal consequences. The Grand Duke of Moscow was an 'older brother', the other dukes were 'younger ones'. Such a form of inter-ducal relations had legal, political and ideological implications. The recognition of one's seniority by a younger duke-brother was an act of his conscious choice (alternatively will) or duress. The second part of the article is a historiographical research into history of Rus. The author examines historical writing of the second half of the nineteenth century. The terminology used in the nineteenth century historical literature shows on the one hand a specific development of Slav lands', and a similarity with Western European countries, on the other hand. I.e. zakladniczetwo was believed to be similar with commendation and pomiesti with benefice. It was Michajlowicz Solowjow (1820-1879) who saw similarities between various institutions, but at the same time emphasized the existence of two types of 'socio-economic systems'. One of them - feudal system, was characteristic of German states, the other one - inter-ducal family relations, typical of Slavic states. The Russian historian, who rejected approaches of both: 'Slavofils' and 'Westernisers', and who advanced the thesis, that socio-economic system of Rus was indeed feudal, was Nikolaj Pawlowicz Pawlow-Silwanski (1869-1908). He showed, that in Rus all elements of feudalism were present, i.e. the problem of partitioning of power connected with the development of jurisdiction granted to feudal lords and bojarszczina. This concept was further developed by Aleksander Jewgieniewicz Priesniakow (1870-1929), the disciple of Sergiej Platonow.