It differs from day-to-day spoken English in a variety of ways including the use of specialized vocabulary, syntactic constructions, and set phrases such as legal doublets.
The use of Law French during this period had an enduring influence on the general linguistic register of modern legal English.
In 1362, the Statute of Pleading was enacted, which stated that all legal proceedings should be conducted in English (but recorded in Latin).
From 1066, Latin was the language of formal records and statutes, and was replaced by English in the Proceedings in Courts of Justice Act 1730.
Examples of mixed language doublets are: "breaking and entering" (English/French), "fit and proper" (English/French), "lands and tenements" (English/French), and "will and testament" (English/Latin).
Thus, the extensive use of French and Latin words in Legal English results in a relatively formal style.
Further, legal English is useful for its dramatic effect: for example, a subpoena compelling a witness to appear in court often ends with the archaic threat "Fail not, at your peril"; the "peril" is not described (being arrested and held in contempt of court) but the formality of the language tends to have a stronger effect on the recipient of the subpoena than a simple statement like "We can arrest you if you don't show up".
According to Walter Probert, judicial lawyers, roughly starting in the twentieth century, often manipulate the language to be more persuasive of their campaign ideals.