Common law forms the basis of the legal system in England and other English-speaking countries, especially those that were former British colonies, including Brunei, Canada except for Quebec, Hong Kong, the Philippines, Sri Lanka, and the United States with the exception of Louisiana. Louisiana, Quebec, and South Africa are said to have a pluralistic legal system combining civil, common, customary, and religious law. Furthermore, Louisiana and Quebec use French law, while the South African legal system is based on Roman-Dutch law. India uses a mixture of Hindu and English law.

Common law was invented in England by three courts – King’s Bench, Exchequer, and the Court of Common Pleas – in order to establish a system of law that could supersede the judgments of local courts. Also, in terms of its application to civil law, common law was used to compensate people who committed wrongful acts, known as torts.

The term common law can also refer to the precedent-based element within the legal system, as opposed to statutory law and legislation. The reasoning used to interpret common law is known as casuistry. It is a strict, principle-based reasoning that uses the circumstances of a case to evaluate the laws that are applicable. Decisions made about similar cases in the past are valuable, and casuistry is consequently also known as case-based learning. The case in question is evaluated on the basis of past cases, called paradigms. The strength of the similarity among the cases, in turn, strengthens the reasoning based on them.

The term common law also underlines the fact that this type of law did not originate from equity, maritime, and other special branches of law. Statues serve as brief explanations of common law, and therefore are not very explanatory. Codification is the process by which a statue is passed, in a single document, so that it is understood within existing common law rather than creating the need for new laws.

Judges create common law by writing opinions about cases that bind lower courts in lower jurisdictions. The foundation for common law is formed by torts, property, and contracts. Each state in the US is responsible for its common law, and the system evolves constantly. Federal common laws apply to issues that are not already addressed by statutes.