Common Law

Common law is a term used to refer to law that is developed through decisions of the court, rather than by relying solely on statutes or regulations. Also known as “case law,” or “case precedent,” common law provides a contextual background for many legal concepts. Common laws vary depending on the jurisdiction, but in general, the ruling of a judge is often used as a basis for deciding future similar cases. To explore this concept, consider the following common law definition.

Definition of Common Law


  1. Laws that are based on court or tribunal decisions, which govern future decisions on similar cases.


1300-1350       Middle English

What is Common Law

Common law often refers to laws that are based on the customs and principles of society, which are used in court case decisions in situations not covered by civil law statutes. These decisions set a precedent that must be applied to future cases on the same subject. Common law only refers to civil cases, and has no bearing on criminal court cases.

While the term common law is used to refer to principles applied to court decisions, a common law system refers to a legal system that places great weight on judicial decisions made in prior similar cases. In the United States, common law, or precedent, is used to help ensure similar results in similar cases. Courts are bound by the decisions of higher courts on similar matters, by a principle of “stare decisis.” If the court determines a case to be fundamentally different from prior cases heard by other courts, its decision is likely to create precedent for future cases on that subject.

History of Common Law

Common law is a term that was originally used in the 12th century, during the reign of Henry II of England. The ruler established secular tribunals, with the goal of establishing a unified system of deciding legal matters. The King’s judges in these tribunals respected the decisions of one another, such decisions creating a unified “common” law throughout England. The precedent set by the courts through the 12th and 13th centuries were often based on tradition and custom, and became known as a “common law” system.

Common law in the United States dates back to the arrival of the colonists, who brought with them the system of law with which they were most familiar. Following the American Revolution, the newly formed states adopted their own forms of common law, separate from the federal law.

Systems of Common Law vs. Civil Statutory Law

Systems of common law and civil statutory law differ in many ways. Rulings in a common law system rely heavily on prior decisions made in similar cases. Rulings in a statutory law system are based primarily statutory laws. This makes the method by which laws are developed and enacted. While common laws develop over time as judicial decisions are made, and used in future decisions, they generally do not become statutory laws enforceable by law enforcement or enforcement agencies. It takes time for the influence of common laws to spread and become common knowledge.

Statutory laws, on the other hand, rely on the legislative process, in which laws and ordinances are developed and voted on by representatives of the people. Once these new laws go into effect, they are enforceable by law enforcement or governmental agencies, and the letter of the law is usually applied in court. Because common law is based on judicial opinion, parties to a civil lawsuit may draw comparisons between precedent-setting cases. Statutory law does not allow for comparisons. For example, civil statutory laws govern such things as deadlines and statutes of limitations, allowed monetary damages, and sentencing.

Many countries rely on either the common law system, or a civil statutory law system. In the United States, the judicial system is a combination of the two, with statutory laws being applied where appropriate, while requiring the courts to adhere to precedent in determining cases not governed by statute.

Federal Common Law

The use of common law by federal courts is limited to deciding federal cases. While, in certain circumstances, federal court may have jurisdiction to hear a case under state law (known as “diversity jurisdiction”), it cannot create or apply federal common law or precedent to deciding a state law case. Rather, a federal judge hearing such a case must turn to state law precedent.

Supreme Court Ruling on Common Law in Diversity Cases

On July 27, 1934, Harry Tompkins was walking on a narrow footpath by the Erie Railroad tracks in Hughestown, Pennsylvania. As a train approached, something protruding from one of the railcars struck Tompkins and knocked him down, causing his arm to be crushed beneath a train wheel. The train was operated by a corporation registered in New York, so Tompkins filed his civil lawsuit in federal district court.

The district court judge who heard the case followed current federal law of the time, in applying federal common law to the case, rather than common law of either the state of Pennsylvania or New York. Federal common law applied a standard of “ordinary negligence” when determining what level of care the railroad owed to individuals who are not employed by the railroad. Common law in the state of Pennsylvania, where the accident occurred, specifies that the railroad owes a “wanton negligence” duty of care to trespassers, which requires proof of a greater level of negligence. The court found in Tompkins’ favor, and awarded him damages.

Prior to the case of Tompkins v. Erie Railroad, it had already been determined that, when a case is heard in federal court in diversity, meaning that the case is filed in federal court because it crosses state jurisdictions, the state’s statutory law must be applied. It had also been ruled, however, that a federal court hearing a case in diversity was not required to apply the state’s common law, or precedent, to the case.

The railroad appealed the matter to the appellate court, then to the U.S. Supreme Court. After reviewing the case, the Supreme Court ruled that the federal district court did not have the authority to create federal common law when reviewing state law claims in diversity, but must apply state common law.

This topic was quite important, as it was an effort by the Supreme Court to address the issue of “forum shopping,” where plaintiffs in cases that cross jurisdictions take their case to the state or jurisdiction whose laws would give them the greatest advantage. With this decision, the Court overturned federal civil procedures, creating a mandate that federal common law should be applied only to strictly federal cases, and not to diversity cases.

Related Legal Terms and Issues

  • Affirm – To uphold a lower court’s decision.
  • Binding Precedent – A rule or principle established by a court, which other courts are obligated to follow.
  • Civil Lawsuit – A lawsuit brought about in court when one person claims to have suffered a loss due to the actions of another person.
  • DefendantA party against whom a lawsuit has been filed in civil court, or who has been accused of, or charged with, a crime or offense.
  • Diversity Jurisdiction – Jurisdiction of a U.S. federal court to hear a case between residents of different states, if it meets a specified monetary threshold.
  • Jurisdiction – The legal authority to hear legal cases and make judgments; the geographical region of authority to enforce justice.
  • PlaintiffA person who brings a legal action against another person or entity, such as in a civil lawsuit, or criminal proceedings.
  • Stare Decisis – The principle that cases based on similar facts should be decided in a consistent manner, with similar results.

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