Common Law: Legal Systems

Common law legal systems have three distinctive elements: judicial decisions are sources of law, judges play passive roles at trials, and juries resolve fact disputes. The United Kingdom, the United States, and most other former English colonies have common law legal systems. Most continental European countries and their former colonies have a civil law legal system, as does Louisiana, whose legal system was established when Spain and France exercised sovereignty over that jurisdiction. In civil law systems, judicial decisions are not sources of law, judges play an active role at trial, and juries play a much reduced role.

The most distinctive element of a common law legal system is, unsurprisingly, the common law. Common law is judge-made law, or legal decisions whose foundations are provided by previous judicial decisions. Judges on common law cases interpret legal rulings in cases with similar facts rather than using legislation or constitutional provisions. For example, in the famous case of MacPher-son v. Buick Motor Company, 217 N.Y. 382 ( 1916 ), Judge Benjamin N. Cardozo ( 1870–1938

Judges in common law systems also use common law methods when engaging in statutory and constitutional interpretation. Courts interpreting the free exercise clause of the First Amendment or the Voting Rights Act of 1965 rely on the text of those measures, the history of those measures, and previous judicial decisions interpreting those measures. When discussing the extent to which school districts could rely on racial classifications, the opinions in Parents Involved in Community Schools v. Seattle School District No. 1, 551 U.S. 701 ( 2007 ), spent far more time interpreting the Supreme Court's decision in Brown v. Board of Education, 347 U.S. 483 ( 1954 ), than they did interpreting the equal protection clause of the Fourteenth Amendment. Judges in common law systems may not, however, treat judge-made law as higher than statutes or constitutional provisions. Congress may overturn judicial decisions interpreting a federal statute by passing a statute with clear language. Congress may similarly overturn judicial decisions interpreting the Constitution by proposing a constitutional amendment that is subsequently ratified by the states.

Common law trials are structured by the adversary system. In common law legal systems, each party is responsible for producing the relevant evidence or making the relevant legal arguments. Judges may not ask questions of the witness, insist that certain witnesses be called, or make independent motions to obtain relevant evidence. If, for example, neither the prosecution nor the defense in a murder trial wishes to introduce available DNA evidence, the trial judge may not independently produce that evidence for the jury. Judges are also expected to make decisions based entirely on the legal arguments raised by the parties. If a defendant in a murder trial consciously elects not to challenge the constitutionality of capital punishment, the trial judge will normally not consider whether the death penalty is constitutional. Alabama Legislative Black Caucus v. Alabama, 135 S. Ct. 1257 ( 2015 ), illustrates the passivity of common law judges. The issue in that case was whether the Alabama Legislative Black Caucus at trial argued that the Alabama state legislature violated the Constitution when determining the boundaries for specific legislative districts. The majority opinion claimed that argument had been made, if not clearly. The dissent denied the argument had been made. The justices were nevertheless united in their belief that they could rule on the constitutionality of particular legislative districts in Alabama only if the plaintiff had actually argued that particular districts were unconstitutionally drawn.

Juries are a staple of common law legal systems. Modern legal theory assigns juries the responsibility for finding facts and judges the responsibility for determining law. In a murder trial, for example, the judge will instruct the members of the jury that they are to find the defendant guilty if and only if they conclude that the defendant killed the victim, that the killing was premeditated, and that the killing was not done in self-defense. In practice, however, juries may exercise some control over the law. Throughout American history, juries have found defendants who have broken unpopular laws not guilty. In some communities, for example, juries are unlikely to convict a defendant for a minor drug crime, such as smoking a joint, even when presented with overwhelming evidence that the defendant once did so. A jury verdict of not guilty cannot be appealed as against the weight of the evidence, even when the judge is convinced that the jury made a mistake or made no effort to apply the law. A jury verdict of guilty can be appealed as against the weight of the evidence if on the basis of the evidence no reasonable person could believe the defendant guilty (defendants may also appeal if some evidence was unconstitutionally or illegally admitted at their trial). Jury verdicts in civil cases may also be appealed, but only if no reasonable person would agree with the verdict. Such appeals are rarely successful.

Globalization and constitutional borrowing are blurring the sharp differences between common law and civil law legal systems. European justices are increasingly inclined to treat past precedents as sources of law. American justices are becoming more aggressive at trial even as their counterparts overseas become less aggressive. Jury trials are rapidly being replaced by plea bargains and judicially encouraged settlements. Nevertheless, as any lawyer who has either moved to or from Louisiana, the one civil law jurisdiction in the United States, can attest, the private law of contracts, torts, and property still differs substantially between civil law and common law jurisdictions.

SEE ALSO Common Law .


Cardozo, Benjamin N. The Nature of the Judicial Process. New Haven, CT: Yale University Press, 1921.

Holmes, Oliver Wendell, Jr. The Common Law. Boston: Little, Brown, 1881.

Merryman, John Henry, and Rogelio Pérez-Perdomo. The Civil Law Tradition: An Introduction to the Legal Systems of Europe and Latin America. 3rd ed. Palo Alto, CA: Stanford University Press, 2007.

Shapiro, Martin. Courts: A Comparative and Political Analysis. Chicago: University of Chicago Press, 1981.

Mark A. Graber
University of Maryland Carey School of Law