«Justice», «law», «liberty» are the key categories of political theory of John of Salisbury (1115/1120-1180), famous English intellectual, outstanding diplomat and philosopher. Analyzing these categories, the researcher represented a sufficiently complete doctrine of power formulated in the treatise «Policraticus, or On the frivolities of courtiers and the footprints of philosophers» («Policraticus, sive de nugis curialium et vestigiis philosophorum»). John of Salisbury, after studying liberal arts («artes liberales») and philosophy at schools of Paris and Chartres, became a secretary and counselor of Theobald, archbishop of Canterbury, and later - of Thomas Becket. Also John was an official representative of the archiepiscopal curia at the papal court and «curia Regis». «Magister from Old Sarum», an influential defender of the church’s liberties and papal authority and one of the most prominent figures of Renaissance of the twelfth century’ European cultural space, supported his friend and patron, the head of the English church, Thomas, archbishop of Canterbury, in political and ecclesiastical conflict with Henry II Plantagenet. After Becket’s murder John was elected bishop of Chartres, where he remained until his death in 1180. As he belonged to the 12th century culture, John, as well as most of his intellectual contemporaries, aimed to gloss of classical law categories in complicated sense uniting antique traditions, represented by Aristotle and Cicero, and patristic (St. Augustine, etc.). Synthesis of pagan and Christian discourses allowed John of Salisbury to create in his «Policraticus», completed in 1159, dedicated to chancellor Thomas Becket (who became an archbishop in 1162) and reflected the author’ philosophical and political views. Also, he introduced to the reader his reaction on the different intellectual, political and ecclesiastical problems of the twelfth century - a theory, where, in the researchers’ opinion, there is no self-contradictions. Distinguishing a «divine» justice, which is equated with equality and «earthly» justice in the patristic tradition, the scholastic noticed that any secular state is guided by the latter, while the former, as the ideal justice, is the highest destiny. The aim of having a sacral power sovereign who yields to priesthood in dignity is reaching a «divine justice», which is impossible without law (i. e. «God’s law») domination and liberty (in its Christian sense, i.e. «free will», that means the right of choice between good and evil).