What is common law?

“Common law” as opposed to “statutory law” is the body of law derived from judicial opinions or decisions in particular cases, rather than from statutes, constitutions, or treaties, that have express provisions creating rights, obligations, and causes of action. Although the term “common law” is frequently used in the study and practice of the legal system, the laws of the United States, and even in some areas of International Law, it is difficult to define this bulk of legal doctrines and concepts, primarily because the common law touches on virtually all areas of the law as a whole. 

Laws that fall under the scope of the common law are historical descendants of the English legal system that was in place prior to the discovery and subsequent colonization of the United States. The traditional English legal system was distinct from other civil law systems around the world. Civil law and common law are often pitted against each other as the two most prominent forms of legal systems in the Western World. Civil law, however, developed at the height of the Roman empire and is still commonly utilized throughout Europe and in Latin America.

In the United States’ judicial system, there term “Federal common law” has been used to refer to the body of case law that has been derived from cases adjudicated by the federal courts that contain federal questions and other issues that concern the federal government such as disputes between citizens of different states (i.e. diversity of citizenship cases). The federal common law, however, excludes those cases that are predominately governed by state law.

“General federal common law” is similar to the federal common law in that it is case law derived from judicial opinions issued by the federal courts sitting in diversity of citizenship. This was so in the period before the landmark case of Erie v. Tompkins, 304 U.S. 64, 58 S. Ct. 817 (1938). Following the Supreme Court’s holding in Erie, federal courts are now required to apply the substantive (but not the procedural) laws of the state in which the particular federal court sits. Although the court made clear in Erie that there is no longer a general federal common law applicable to all disputes heard in federal courts, the notion of at least some “federal common law” continues to persist today.

While the term “common law” may be used quite frequently among legal scholars and legal practitioners alike, the bounds of this legal notion are quite fluid. As such, a basic understanding of common law as a whole would require an in-depth exploration of the ‘common laws’ of various sub-fields within the law, including Property Law, Contract Law, and Criminal Law.