A treatise is a formally written document focused on one legal subject. Normally, it is a large secondary source book on a given subject. These books reference appropriate primary sources for their subjects. There are no limitations to what may be called a treatise in the legal arena; some case study books, parts of a larger series, and textbooks are all called treatises.
Legal professionals working in a new area of the law for the first time might refer to one of these books to familiarize themselves with a specific area of law. The summary document provides the professional with the information necessary to glean a basic understanding of a particular area of the law. The professional also uses the treatise as a tool to help reach the detailed information that may be used as a source by the professional.
Law students might use a treatise as an additional source to assist them to find more information about a given subject. Legal textbooks vary in the detail they provide on each subject. Sometimes it is necessary for a law student to search out secondary materials to complete the picture. These types of treatises might be called hornbooks.
Students may purchase these secondary materials along with their textbooks. First-year law students are likely to buy a general treatise that includes basic legal definitions and explanations. These books are helpful for the students as they learn a new vocabulary, because the law includes a large number of words and phrases not used in regular conversation.
Most legal treatises are generally found in law libraries. This is one of the instances where the individual should look for the physical book versus using an online tool. Many forms of legal research are housed in online forums, but most treatises are limited to book format. Research for the most appropriate treatise begins in the law library’s catalog system.
A legal treatise may cover broad subject matter such as contract law or it might focus on a very particular topic such as a specific law. As one is familiarizing oneself with an area of law, one may begin with the book that covers the broad subject matter and then work toward more detail in another book. Each should have references to primary sources that allow one to get to a particular law in the correct jurisdiction to cite in one’s case.