In common law legal systems, precedent is a principle or rule established in a previous legal case that is either binding on or persuasive for a court or other tribunal when deciding subsequent cases with similar issues or facts. Common-law legal systems place great value on deciding cases according to consistent principled rules, so that similar facts will yield similar and predictable outcomes, and observance of precedent is the mechanism by which that goal is attained. The principle by which judges are bound to precedents is known as stare decisis (a Latin phrase literally means, "Let the decision stand"). Common-law precedent is a third kind of law, on equal footing with statutory law (that is, statutes and codes enacted by legislative bodies) and subordinate legislation - that is, delegated legislation (in U.K. parlance) or regulatory law (in U.S. parlance) (that is, regulations promulgated by executive branch agencies).
In the common-law tradition, courts decide the law applicable to a case by interpreting statutes and applying precedent, which record how and why prior cases have been decided. Unlike most civil-law systems, common-law systems follow the doctrine of stare decisis, by which most courts are bound by their own previous decisions in similar cases, and all lower courts should make decisions consistent with previous decisions of higher courts. For example, in England, the High Court and the Court of Appeal are each bound by their own previous decisions, but the Supreme Court of the United Kingdom is able to deviate from its earlier decisions, although in practice it rarely does so.
In law, a binding precedent (also known as a mandatory precedent or binding authority) is a precedent which must be followed by all lower courts under common law legal systems. In English law it is usually created by the decision of a higher court, such as the Supreme Court of the United Kingdom, which took over the judicial functions of the House of Lords in 2009. In Civil law and pluralist systems precedent is not binding but case law is taken into account by the courts.
The U.S. Supreme Court has final authority on questions about the meaning of federal law, including the U.S. Constitution. For example, when the Supreme Court says that the First Amendment applies in a specific way to suits for slander, then every court is bound by that precedent in its interpretation of the First Amendment as it applies to suits for slander. If a lower court judge disagrees with a higher court precedent on what the First Amendment should mean, the lower court judge must rule according to the binding precedent. Until the higher court changes the ruling (or the law itself is changed), the binding precedent is authoritative on the meaning of the law.
A judge in a subsequent case, particularly in a different jurisdiction, could find the dissenting judge's reasoning persuasive. In the jurisdiction of the original decision, however, a judge should only overturn the holding of a court lower or equivalent in the hierarchy. A district court, for example, could not rely on a Supreme Court dissent as a basis to depart from the reasoning of the majority opinion. However, lower courts occasionally cite dissents, either for a limiting principle on the majority, or for propositions that are not stated in the majority opinion and not inconsistent with that majority, or to explain a disagreement with the majority and to urge reform (while following the majority in the outcome).
Nonpublication of opinions, or unpublished opinions, are those decisions of courts that are not available for citation as precedent because the judges making the opinion deem the cases as having less precedential value. Selective publication is the legal process which a judge or justices of a court decide whether a decision is to be or not published in a reporter. "Unpublished" federal appellate decisions are published in the Federal Appendix. Depublication is the power of a court to make a previously published order or opinion unpublished.
By definition, a case of first impression cannot be decided by precedent. Since there is no precedent for the court to follow, the court uses the plain language and legislative history of any statute that must be interpreted, holdings of other jurisdictions, persuasive authority and analogies from prior rulings by other courts (which may be higher, peers, or lower courts in the hierarchy, or from other jurisdictions), commentaries and articles by legal scholars, and the court's own logic and sense of justice.
Stare decisis is not usually a doctrine used in civil law systems, because it violates the legislative positivist principle that only the legislature may make law. Instead, the civil law system relies on the doctrine of jurisprudence constante, according to which if a court has adjudicated a consistent line of cases that arrive at the same holdings using sound reasoning, then the previous decisions are highly persuasive but not controlling on issues of law. This doctrine is similar to stare decisis insofar as it dictates that a court's decision must condone a cohesive and predictable result. In theory, lower courts are generally not bound by the precedents of higher courts. In practice, the need for predictability means that lower courts generally defer to the precedent of higher courts. As a result, the precedent of courts of last resort, such as the French Cassation Court and the Council of State, is recognized as being de facto binding on lower courts.
Precedent viewed against passing time can serve to establish trends, thus indicating the next logical step in evolving interpretations of the law. For instance, if immigration has become more and more restricted under the law, then the next legal decision on that subject may serve to restrict it further still. The existence of submerged precedent (reasoned opinions not made available through conventional legal research sources) has been identified as a potentially distorting force in the evolution of law.