The term common law has many connotations. The first three set out here are the most-common usages within the legal community. Other connotations from past centuries are sometimes seen, and are sometimes heard in everyday speech.
Common law as opposed to statutory law and regulatory law
The first definition of "common law" given in Black's Law Dictionary, 10th edition, 2014, is "The body of law derived from judicial decisions, rather than from statutes or constitutions; [synonym] CASELAW, [contrast] STATUTORY LAW."  This usage is given as the first definition in modern legal dictionaries, is characterized as the “most common” usage among legal professionals, and is the usage frequently seen in decisions of courts. In this connotation, "common law" distinguishes the authority that promulgated a law. For example, the law in most Anglo-American jurisdictions includes "statutory law" enacted by a legislature, "regulatory law" (in the U.S.) or “delegated legislation” (in the U.K.) promulgated by executive branch agencies pursuant to delegation of rule-making authority from the legislature, and common law or "case law", i.e., decisions issued by courts (or quasi-judicial tribunals within agencies). This first connotation can be further differentiated into
- (a) pure common law
- arising from the traditional and inherent authority of courts to define what the law is, even in the absence of an underlying statute or regulation. Examples include most criminal law and procedural law before the 20th century, and even today, most contract law and the law of torts.
- (b) interstitial common law
- court decisions that analyze, interpret and determine the fine boundaries and distinctions in law promulgated by other bodies. This body of common law, sometimes called "interstitial common law", includes judicial interpretation of the Constitution, of legislative statutes, and of agency regulations, and the application of law to specific facts.
Publication of decisions, and indexing, is essential to the development of common law, and thus governments and private publishers publish law reports. While all decisions in common law jurisdictions are precedent (at varying levels and scope as discussed throughout the article on precedent), some become "leading cases" or "landmark decisions" that are cited especially often.
Common law legal systems as opposed to civil law legal systems
Black's Law Dictionary 10th Ed., definition 2, differentiates "common law" jurisdictions and legal systems from "civil law" or "code" jurisdictions. Common law systems place great weight on court decisions, which are considered "law" with the same force of law as statutes—for nearly a millennium, common law courts have had the authority to make law where no legislative statute exists, and statutes mean what courts interpret them to mean.
By contrast, in civil law jurisdictions (the legal tradition that prevails, or is combined with common law, in Europe and most non-Islamic, non-common law countries), courts lack authority to act if there is no statute. Civil law judges tend to give less weight to judicial precedent, which means that a civil law judge deciding a given case has more freedom to interpret the text of a statute independently (compared to a common law judge in the same circumstances), and therefore less predictably. For example, the Napoleonic code expressly forbade French judges to pronounce general principles of law. The role of providing overarching principles, which in common law jurisdictions is provided in judicial opinions, in civil law jurisdictions is filled by giving greater weight to scholarly literature, as explained below.
Common law systems trace their history to England, while civil law systems trace their history through the Napoleonic Code back to the Corpus Juris Civilis of Roman law.
Law as opposed to equity
Black's Law Dictionary 10th Ed., definition 4, differentiates "common law" (or just "law") from "equity". Before 1873, England had two complementary court systems: courts of "law" which could only award money damages and recognized only the legal owner of property, and courts of "equity" (courts of chancery) that could issue injunctive relief (that is, a court order to a party to do something, give something to someone, or stop doing something) and recognized trusts of property. This split propagated to many of the colonies, including the United States. For most purposes, most jurisdictions, including the U.S. federal system and most states, have merged the two courts. Additionally, even before the separate courts were merged, most courts were permitted to apply both law and equity, though under potentially different procedural law. Nonetheless, the historical distinction between "law" and "equity" remains important today when the case involves issues such as the following:
- categorizing and prioritizing rights to property—for example, the same article of property often has a "legal title" and an "equitable title", and these two groups of ownership rights may be held by different people.
- in the United States, determining whether the Seventh Amendment's right to a jury trial applies (a determination of a fact necessary to resolution of a "common law" claim) vs. whether the issue will be decided by a judge (issues of what the law is, and all issues relating to equity).
- the standard of review and degree of deference given by an appellate tribunal to the decision of the lower tribunal under review (issues of law are reviewed de novo, that is, "as if new" from scratch by the appellate tribunal, while most issues of equity are reviewed for "abuse of discretion", that is, with great deference to the tribunal below).
- the remedies available and rules of procedure to be applied.
Courts of equity rely on common law principles of binding precedent.
Archaic meanings and historical uses
In addition, there are several historical (but now archaic) uses of the term that, while no longer current, provide background context that assists in understanding the meaning of "common law" today.
In one usage that is now archaic, but that gives insight into the history of the common law, "common law" referred to the pre-Christian system of law, imported by the Saxons to England, and dating to before the Norman conquest, and before there was any consistent law to be applied. That usage is obsolete today. It is both underinclusive and overinclusive, as discussed in the section on "misconceptions".
"Common law" as the term is used today in common law countries contrasts with ius commune. While historically the ius commune became a secure point of reference in continental European legal systems, in England it was not a point of reference at all.
The English Court of Common Pleas dealt with lawsuits in which the Monarch had no interest, i.e., between commoners.
Black's Law Dictionary 10th Ed., definition 3 is "General law common to a country as a whole, as opposed to special law that has only local application." From at least the 11th century and continuing for several centuries after that, there were several different circuits in the royal court system, served by itinerant judges who would travel from town to town dispensing the King's justice in "assizes". The term "common law" was used to describe the law held in common between the circuits and the different stops in each circuit. The more widely a particular law was recognized, the more weight it held, whereas purely local customs were generally subordinate to law recognized in a plurality of jurisdictions.
Misconceptions and imprecise nonlawyer usages
As used by non-lawyers in popular culture, the term "common law" connotes law based on ancient and unwritten universal custom of the people. The "ancient unwritten universal custom" view was the view among lawyers and judges from the earliest times to the mid-19th century. But for 100 years, lawyers and judges have recognized that the "ancient unwritten universal custom" view does not accord with the facts of the origin and growth of the law, and it is not held within the legal profession today.
- Under the modern view, “common law” is not grounded in “custom” or "ancient usage", but rather acquires force of law instantly (without the delay implied by the term "custom" or "ancient") when pronounced by a higher court, because and to the extent the proposition is stated in judicial opinion. From the earliest times through the late 19th century, the dominant theory was that the common law was a pre-existent law or system of rules, a social standard of justice that existed in the habits, customs, and thoughts of the people. Under this older view, the legal profession considered it no part of a judge's duty to make new or change existing law, but only to expound and apply the old. By the early 20th century, largely at the urging of Oliver Wendell Holmes (as discussed throughout this article), this view had fallen into the minority view: Holmes pointed out that the older view worked undesirable and unjust results, and hampered a proper development of the law. In the century since Holmes, the dominant understanding has been that common law “decisions are themselves law, or rather the rules which the courts lay down in making the decisions constitute law”. The reality of the modern view can be seen in practical operation: under the old "pre-existing custom" view, (a) jurisdictions could not logically diverge from each other (but nonetheless did), (b) a new decision logically needed to operate retroactively (but did not), and (c) there was no standard to decide which English medieval customs should be "law" and which should not. All three tensions resolve under the modern view: (a) the common law in different jurisdictions may diverge, (b) new decisions need not have retroactive operation, and (c) court decisions are effective immediately as they are issued, not years later, or after they become "custom", and questions of what "custom" might have been at some "ancient" time are simply irrelevant.
- Common law, as the term is used among lawyers in the present day, is not frozen in time, and no longer beholden to 11th, 13th, or 17th century English law. Rather, the common law evolves daily and immediately as courts issue precedential decisions (as explained later in this article), and all parties in the legal system (courts, lawyers, and all others) are responsible for up-to-date knowledge. There is no fixed reference point (for example the 11th or 18th centuries) for the definition of "common law", except in a handful of isolated contexts. Much of what was "customary" in the 13th or 17th or 18th century has no part of the common law today; much of the common law today has no antecedent in those earlier centuries. Among legal professionals (lawyers and judges), the change in understanding occurred in the late 19th and early 20th centuries (as explained later in this article), though lay dictionaries were decades behind in recognizing the change.
- The common law is not "unwritten". Common law exists in writing—as must any law that is to be applied consistently—in the written decisions of judges.
- Common law is not the product of "universal consent". Rather, the common law is often anti-majoritarian.