In the fourth book of the “Ancient Rus'” series, the author shows the consistent maturation of thought in the Russian word - in the unity of feeling and will. The formation of the Old Russian mentality is shown through the main categories of knowledge and consciousness in the constant improvement of forms of knowledge. Ends and beginnings, causes and goals, space and time, quality and quantity and others are examined on extensive ancient Russian material in order to show “from the inside” the events that took place, the difficult path that our ancestors took to the formation of modern mentality in its cognitive aspects. The book may be useful for anyone interested in the development of Russian mentality in its dramatic moments.