English law
Common law is a term with historical origins in the legal system of England. It denotes, in the first place, the judge-made law that developed from the early Middle Ages as described in a work published at the end of the 19th century, "The History of English Law before the Time of Edward I", in which Pollock and Maitland expanded the work of Coke (17th century) and Blackstone (18th century). Specifically, the law developed in England's Court of Common Pleas and other common law courts, which became also the law of the colonies settled initially under the crown of England or, later, of the United Kingdom, in North America and elsewhere; and this law as further developed after those courts in England were reorganised by the Supreme Court of Judicature Acts passed in the 1870s, and developed independently, in the legal systems of the United States and other jurisdictions, after their independence from the United Kingdom, before and after the 1870s. The term is used, in the second place, to denote the law developed by those courts, in the same periods (pre-colonial, colonial and post-colonial), as distinct from within the jurisdiction, or former jurisdiction, of other courts in England: the Court of Chancery, the ecclesiastical courts, and the Admiralty court.
Mens rea
The levels of "mens rea" and the distinction between them vary between jurisdictions. Although common law originated from England, the common law of each jurisdiction with regard to culpability varies as precedents and statutes vary.
The vast majority of criminal prosecutions in the United States are carried out by the component states in accordance with the laws of the state in question. Historically, the states (with the partial exception of civil-law Louisiana) applied common law rules of "mens rea" similar to those extant in England, but over time American understandings of common law "mens rea" terms diverged from those of English law and from each other. By the late 1950s to early 1960s, the common law of "mens rea" was widely acknowledged to be a slippery, vague, and confused mess. This was one of several factors that led to the development of the Model Penal Code.