Case law is a set of past rulings by tribunals that meet their respective jurisdictions' rules to be cited as precedent. These interpretations are distinguished from statutory law, which are the statutes and codes enacted by legislative bodies, and regulatory law, which are regulations established by executive agencies based on statutes. The term "case law" is applied to any set of previous rulings by an adjudicatory tribunal that guides future rulings; for example, patent office case law.
In common law countries the term is used for judicial decisions of selected appellate courts, courts of first instance, agency tribunals, and other bodies discharging adjudicatory functions. In common law countries, "case law" is a near-exact synonym for "common law".
In common law systems
In the common law tradition, courts decide the law applicable to a case by interpreting statutes and applying precedents 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.
Generally speaking, higher courts do not have direct oversight over the lower courts of record, in that they cannot reach out on their own initiative (sua sponte) at any time to overrule judgments of the lower courts. Normally, the burden rests with litigants to appeal rulings (including those in clear violation of established case law) to the higher courts. If a judge acts against precedent and the case is not appealed, the decision will stand.
A lower court may not rule against a binding precedent, even if it feels that it is unjust; it may only express the hope that a higher court or the legislature will reform the rule in question. If the court believes that developments or trends in legal reasoning render the precedent unhelpful, and wishes to evade it and help the law evolve, it may either hold that the precedent is inconsistent with subsequent authority, or that it should be distinguished by some material difference between the facts of the cases. If that judgment goes to appeal, the appellate court will have the opportunity to review both the precedent and the case under appeal, perhaps overruling the previous case law by setting a new precedent of higher authority. This may happen several times as the case works its way through successive appeals. Lord Denning, first of the High Court of Justice, later of the Court of Appeal, provided a famous example of this evolutionary process in his development of the concept of estoppel starting in the High Trees case: Central London Property Trust Ltd v. High Trees House Ltd  K.B. 130.
How case law is made
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The different roles of case law in civil and common law traditions create differences in the way that courts render decisions. Common law courts generally explain in detail the legal rationale behind their decisions, with citations of both legislation and previous relevant judgments, and often an exegesis of the wider legal principles. The necessary analysis (called ratio decidendi), then constitutes a precedent binding on other courts; further analyses not strictly necessary to the determination of the current case are called obiter dicta, which constitute persuasive authority but are not technically binding. By contrast, decisions in civil law jurisdictions are generally very short, referring only to statutes. The reason for this difference is that these civil law jurisdictions adhere to a tradition that the reader should be able to deduce the logic from the decision and the statutes, so that, in some cases, it is somewhat difficult to apply previous decisions to the facts presented in future cases.
Some pluralist systems, such as Scots law in Scotland and so-called civil law jurisdictions in Quebec and Louisiana, do not precisely fit into the dual "common-civil" law system classifications. Such systems may have been heavily influenced by the Anglo-American common law tradition; however, their substantive law is firmly rooted in the civil law tradition. Because of their position between the two main systems of law, these types of legal systems are sometimes referred to as "mixed" systems of law.
Law professors in common law traditions play a much smaller role in developing case law than professors in civil law traditions. Because court decisions in civil law traditions are brief and not amenable to establishing precedent, much of the exposition of the law in civil law traditions is done by academics rather than by judges; this is called doctrine and may be published in treatises or in journals such as Recueil Dalloz in France. Historically, common law courts relied little on legal scholarship; thus, at the turn of the twentieth century, it was very rare to see an academic writer quoted in a legal decision (except perhaps for the academic writings of prominent judges such as Coke and Blackstone). Today academic writers are often cited in legal argument and decisions as persuasive authority; often, they are cited when judges are attempting to implement reasoning that other courts have not yet adopted, or when the judge believes the academic's restatement of the law is more compelling than can be found in precedent. Thus common law systems are adopting one of the approaches long common in civil law jurisdictions.
Judges may refer to various types of persuasive authority to reach a decision in a case. Widely cited non-binding sources include legal encyclopedias such as Corpus Juris Secundum and Halsbury's Laws of England, or the published work of the Law Commission or the American Law Institute. Some bodies are given statutory powers to issue Guidance with persuasive authority or similar statutory effect, such as the Highway Code.
In federal or multi-jurisdictional law systems there may exist conflicts between the various lower appellate courts. Sometimes these differences may not be resolved and it may be necessary to distinguish how the law is applied in one district, province, division or appellate department. Usually only an appeal accepted by the court of last resort will resolve such differences and, for many reasons, such appeals are often not granted.
Any court may seek to distinguish its present case from that of a binding precedent, in order to reach a different conclusion. The validity of such a distinction may or may not be accepted on appeal. An appellate court may also propound an entirely new and different analysis from that of junior courts, and may or may not be bound by its own previous decisions, or in any case may distinguish them on the facts.
Where there are several members of a court, there may be one or more judgments given; only the ratio decidendi of the majority can constitute a binding precedent, but all may be cited as persuasive, or their reasoning may be adopted in argument. Quite apart from the rules of precedent, the weight actually given to any reported judgment may depend on the reputation of both the reporter and the judges.
The legal systems of the Nordic countries are sometimes included among the civil law systems, but as a separate branch, and sometimes counted as separate from the civil law tradition. In Sweden, for instance, case law arguably plays a more important role than in some of the Continental civil law systems. The two highest courts, the Supreme Court (Högsta domstolen) and the Supreme Administrative Court (Regeringsrätten), have the right to set precedent which is in practice (however not formally) binding on all future application of the law. Courts of appeal, both general courts (hovrätter) and administrative courts (kammarrätter) may also issue decisions that act as guides for the application of the law, but these decisions may be overturned by higher courts.
- Garner, Bryan A. (2001). A Dictionary of Modern Legal Usage (2nd, revised ed.). New York: Oxford University Press. p. 177.
In modern usage, common law is contrasted with a number of other terms. First, in denoting the body of judge-made law based on that developed in England… [P]erhaps most commonly within Anglo-American jurisdictions, common law is contrasted with statutory law ...
- Black's Law Dictionary - Common law (10th ed.). 2014. p. 334.
1. The body of law derived from judicial decisions, rather than from statutes or constitutions; CASE LAW [contrast to] STATUTORY LAW.
- Apple, James G. "A Primer on the Civil-Law System" (PDF). fjc.gov. Retrieved 4 May 2018.