The paper presents an analysis of the work of the American researcher Daniel H. Kaiser “The Growth of Law in Medieval Russia”, reveals the logic and concept of the author. The work was published in 1980, translated into Russian in 2024. Despite the time that has passed since the first edition, the work is practically not outdated. Changes in law from the 13th century to the 15th century are considered against the background of the substitution of “horizontal” relations (direct contacts of the parties to disputes and legal relations) with «vertical» relations involving the intervention of public authorities. The article presents a critique of D. Kaiser's concept from the point of view of modern historical and legal science, its undoubted advantages and inherent contradictions.