In the book "Commentaries to the Laws of England" written by William Blackstone, the author summarized the available legal material, as well as enshrined the rules and methods of interpretation of the law, which are typical for the theory of law at present also. In view of the peculiarities of the legal system of England, Blackston brought the rules of interpretation concerning not only state-established rules of conduct, but also customs. This approach allowed him to acquire and summon their popularity among judges as well as among legal scholars.