The phrase is almost synonymous with “horn law.” There are a number of venerable sources of law that distill the common law on various subjects known as Restatement of the Law. Specific titles will be “The Restatement (First) of Contracts” or “The Restatement of Agency”, etc. Each of these volumes is divided into sections beginning with a text in bold that summarizes a basic rule on an aspect of contract law, agencies, etc. This “restatement” is followed by comments and examples that extend to the principle invoked. . In a case before the U.S. Supreme Court in 1831, Jackson ex dem. Bradstreet Huntington, the phrase “black letter” has been used: “It is rare that a case in our time tastes so much of the black letter; but the conduct of decisions in New York makes it inevitable… ».  The phrase “Black-Letter Law” was used in Naglee v.
Ingersoll, 7 Pa. 185 (1847). The set does not come from the connection with Black`s Law Dictionary, which was first published in 1891. Instead, he probably refers to the practice of writing law books and quoting blackletter-type legal precedents, a tradition that survived long after the passage to the Roman text and awarded for other printed works. In common law, the informal legal doctrine of a black nature contains the fundamental principles of the law, generally accepted by the courts and/or enshrined in the statutes of a particular court. The letter of the law is its effective implementation, thus showing that black laws are statutes, laws, laws, laws, provisions, etc., which have been or have been written in the history of the law of the state concerned or that have been or have been indicated in legal texts. This is often the case for many common law precedents. An example of such a state in the common law jurisdiction, and the use of the black letter doctrine is Canada. Canada is a monarchical state, with its roots in colonial England, and the Black Letter Act is the principles of the law accepted by the majority of judges in most provinces and territories. Sometimes this is called “horn book law,” which means a treaty or manual that is often accepted as authoritarian, competent and general in the field of Canadian law. As a jurist, the law of the horn book or the law of black letters is a fundamental and recognized legal principle, which does not need an additional explanation, since a horn book is a basic basis. The law is the rule that a principle, a provision, references, conclusions, observations, etc., should not require further explanation or clarification if their nature shows that they are fundamental and elementary.
Another synonym usually used in the United Kingdom is the “trite law.” 1-300, 301-600, 601-900, in the laws of the common law, black letter laws are established laws that are no longer questionable.  Some examples are the “Black Letters Act,” which states that contracting requires review, or “schwarzbuchengesetz,” where the registration of a trademark requires well-established use in commercial transactions. The law of the black letter may be contrasted with legal theory or unresolved legal issues.