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Common Law



Common Law, a term used to refer to the main body of English unwritten law that evolved from the 12th century onward. The name comes from the idea that English medieval law, as administered by the courts of the realm, reflected the common customs of the kingdom. This system of law prevails in England and Wales and in those countries, such as Canada and the United States, that were originally colonized by English settlers.


The common law is based on the principle of deciding cases by reference to previous judicial decisions, rather than to written statutes drafted by legislative bodies. Common law can be contrasted to the civil law system, based on ancient Roman law, found in continental Europe and elsewhere. Whereas civil law judges resolve disputes by referring to statutory principles arrived at in advance, common law judges focus more intently on the facts of the particular case to arrive at a fair and equitable result for the litigants.

As the number of judicial decisions accumulates on a particular kind of dispute, general rules or precedents emerge and become guidelines for judges deciding similar cases in the future. Subsequent cases, however, may reveal new and different facts and considerations, such as changing social or technological conditions. A common law judge is then free to depart from precedent and establish a new rule of decision, which sets a new precedent as it is accepted and used by different judges in other cases. In this manner, common law retains a dynamic for change. As the United States Supreme Court Justice Oliver Wendell Holmes wrote in his book The Common Law (1881): “The life of the [common] law has not been logic; it has been experiencing.”

In all common law systems, a pyramidal structure of courts exists to define and refine the law. At the base of the pyramid is the trial court. In criminal trials a judge sits with a jury; the judge decides and instructs the jury on the law, and the jury decides on factual issues. Except for cases of defamation, malicious prosecution, or false imprisonment, which are decided by a jury, in civil actions, a judge sitting alone decides issues of both fact and law.

Above the trial courts, layers of appellate (appeal) courts, composed entirely of judges, exist to adjudicate disputes. These disputes centre on whether or not the trial judge applied the correct principles of law and drew the right conclusions from the factual evidence in civil cases. The interpretations of law made by appellate courts form the precedents that govern future cases. Furthermore, the importance of a precedent for any given court depends on that court’s position in the pyramidal structure; for example, a precedent set by an appellate court has greater force in trial courts than in other appellate courts.


Common law has been known as unwritten law because it is not collected in a single source. Reports of the judicial decisions from which the common law was derived were only occasionally circulated from the 12th to the 16th century. Starting in the 17th century, formal reports of some decisions were published by private parties. These early reports were supplemented by infrequent scholarly treatises summarizing large segments of the case law, such as those of Sir Edward Coke (published in 1628) and Sir William Blackstone (published 1765-1769). As reporting improved, the influence of these treatise writers diminished. In the 19th century, the courts themselves took responsibility for overseeing the publication of judgments in both England and the United States. It is primarily the decisions of appellate rather than trial courts that are published.


Common law is distinguished from other forms of judge-made law from parallel court systems. In medieval times, for example, common law courts were secular, as contrasted with the ecclesiastical courts of the Roman Catholic Church. Common law courts did not deal with merchant law, which was administered in mercantile courts, or with maritime law, administered in the admiralty court.

The most important parallel system was equity jurisdiction. Equity originated in early English law when subjects petitioned the monarch for justice. Such petitions were delegated to Lord Chancellor and later to a tribunal called the Court of Chancery. Equity grew into a special body of rules over and above those administered in other royal courts of law. At first, common law courts were more bound by precedent than were courts of equity, which provided remedies based on notions of fairness to litigants who were denied relief on technical grounds under common law.

By the end of the medieval period, common law and equity constituted the vast bulk of all English law. As common law became less formal and as equity accumulated its own set of precedents, these two forms of judge-made law grew closer together. Britain abolished the distinction between common law and equity in the Judicature Act of 1873. The ultimate effect of the growth and absorption of equity jurisdiction was to gradually expand the range of disputes that could be adjudicated in formal courts.

During and after the Industrial Revolution, in response to the growing complexity of the law and the need for greater clarity and accessibility, the British parliament asserted itself as the principal source of new law, modifying and adding to the body of judge-made law by statute. In modern times, the statutes of Parliament have come to encompass most legal relationships. The common law, however, remains in force to help interpret statutes, many of which are primarily restatements of common law rules and principles.


Most of the English common law, as it existed at the time of the American War of Independence, became the foundation of a distinctly American system of law. Common law has varied from state to state, but only one state, Louisiana, differs significantly from the rest, basing its system on the French civil law model.

See also Administrative Law; International Law.