Common law is law developed through judicial decisions, and the term also describes the legal tradition that originated in England and gives precedent an important role. In the United States, common-law principles operate alongside constitutions, statutes and regulations; they are not permission for judges to disregard written law.

A useful starting question is: Does “common law” describe a legal system, a particular rule, or a specialized phrase such as common-law marriage? Identifying that meaning prevents a common mistake: assuming every court decision creates a new rule, or that a statute makes earlier decisions irrelevant.

Common law, precedent and stare decisis

These terms connect, but they do different jobs:

• Common law: rules developed through decisions, often by applying and adapting earlier reasoning to new disputes.
• Case law: the body of reported judicial decisions; case law includes decisions interpreting constitutions and statutes as well as common-law rules.
• Precedent: an earlier decision whose legal reasoning or holding bears on a later issue; its authority depends on the court, jurisdiction and question decided.
• Stare decisis: the principle of following precedent, with rules about when a court may reconsider its own decisions.
• Statutory law: law enacted by a legislature, such as Congress or a state legislature.

A decision applying a statute is precedent without necessarily creating a freestanding common-law rule. Likewise, a judge's observation about an issue the court did not need to decide does not automatically bind later courts.

The federal district court's plain-language precedent definition is a useful introduction. For an actual dispute, however, court hierarchy matters more than whether a reader thinks an older decision was mistaken.

Common law versus statutory law and civil law

“Civil law” has two meanings. In a legal-system comparison, it means the civil-law tradition. In a courthouse discussion, it may mean noncriminal matters, such as a contract lawsuit. A civil lawsuit in an American common-law jurisdiction does not become a civil-law-system case simply because it is not criminal.

Nor are the traditions opposites in which one uses only decisions and the other only statutes. The Federal Judicial Center's comparison of legal traditions explains that common-law countries have extensive legislation, while civil-law countries also use judicial decisions, sometimes with significant precedential authority. Mixed systems and local variations make absolute labels unreliable.

How to work out which authority controls

For a U.S. legal question, use this sequence: identify the governing jurisdiction → read applicable written law → find controlling interpretations → compare the material facts. The sequence is a research framework, not a guarantee that the answer will be simple.

1. Identify the jurisdiction and issue. A state contract question, a federal constitutional question and a federal statutory question can involve different sources of law. Filing in federal court does not make every issue federal law.
2. Check the court hierarchy. A controlling higher-court holding generally binds a lower court within the relevant hierarchy. A decision from another jurisdiction may be persuasive rather than binding; a trial-court decision is not automatically binding on another trial judge.
3. Compare what was actually decided. Look at the legal issue, holding and materially relevant facts. A case about interpreting a statute is not necessarily authority for a different common-law claim. Distinguishing a case requires a legally meaningful difference, not simply a preferred result.
4. Check for later changes. Read amendments, effective dates, overruling decisions and current treatment. Ask whether a statute displaced the earlier rule, preserved part of it, or left an issue for courts to resolve. An old quotation alone cannot establish today's rule.

In Rodriguez de Quijas v. Shearson/American Express, the Supreme Court instructed lower federal courts to follow its directly controlling precedent and leave overruling to that Court, even when other decisions appeared to undermine the precedent's reasoning. “The judge thinks it is wrong” is not a general exception to binding authority.

What happens when a statute and common law conflict?

A valid, applicable statute generally controls over a conflicting common-law rule, subject to governing constitutional limits. But first determine whether there really is a conflict: the statute may regulate only one part of a relationship, leave other common-law rules intact, or require interpretation itself.

Courts' interpretations of that statute can then become important precedent. Written law and case law therefore interact; they are not competing sources from which a judge simply chooses a favorite. Statutory language, jurisdiction and later authority matter more than a blanket slogan that “statute always beats cases.” A constitutional holding presents a different question from a court-created rule that a legislature can change.

Hypothetical negligence example: A customer slips in a shop. Earlier state cases explain the care a shopkeeper owes customers. Suppose an applicable state statute also imposes a specific inspection requirement. A court would read that statute, check controlling decisions about its effect, and assess the relevant facts. Whether a violation establishes negligence, supplies evidence, or has some other consequence depends on that jurisdiction's law; the accident alone does not decide liability.

Hypothetical contract example: Two businesses dispute whether an exchange created an enforceable agreement. Earlier cases may explain general contract principles. Suppose an applicable enactment requires this type of agreement to be in writing. The court must examine the enactment, any exceptions and controlling interpretations before applying broader contract principles. Calling the dispute “common law” does not erase the statutory requirement or establish that an exception applies.

These fictional examples illustrate a method, not the outcome of a particular state's case.

How common law operates in the United States

The English common-law tradition influenced American law, but American jurisdictions developed their own institutions, statutes and decisions. State law is central to many ordinary private-law disputes. The applicable state's law must be identified rather than assuming one nationwide set of judge-made rules.

For federal civil cases, the Rules of Decision Act, 28 U.S.C. § 1652, directs use of state laws where they apply, except where the Constitution, treaties or Acts of Congress otherwise require or provide. In Erie Railroad Co. v. Tompkins, the Supreme Court rejected federal general common law and recognized that applicable state law includes judicial decisions as well as statutes.

That does not mean federal common law never exists. In Rodriguez v. FDIC, the Court emphasized its limited role, referring to areas such as admiralty and interstate disputes. It rejected the particular federal tax-refund allocation rule at issue and remanded; it did not decide who ultimately owned the refund under state law. A federal setting alone does not authorize a court to invent a general rule.

A short history, and two phrases that need care

Common law developed in medieval England as royal courts and traveling judges helped establish rules applied across the realm. Over time, recorded decisions and reasoning from earlier cases became important to the tradition. That history explains the name; it does not mean every old English rule remains current American law.

Two familiar phrases have more specific meanings:

• Common-law marriage: a form of legally recognized marriage available under the law of particular jurisdictions, not a general reward for living together. The Texas State Law Library's guide describes agreement to marry, living together in Texas after that agreement, and representing to others that the couple is married. It explains that Texas has no fixed minimum cohabitation period and recognizes same-sex informal marriages. Eligibility, proof and recognition still require the applicable law; there is no nationwide “seven-year marriage” rule.
• Common-law crimes: do not assume historical offenses can be prosecuted everywhere without legislation. For example, Minnesota Statutes § 609.015 abolishes common-law crimes while allowing common-law rules to inform statutory interpretation. That is a labeled state example, not a statement of every jurisdiction's criminal law.

Common questions about common law

What does common law mean in simple terms?

It often means legal rules developed through court decisions. It can also mean the broader English-origin legal tradition. The surrounding sentence tells you which meaning is intended.

Does the United States use common law?

Yes, the common-law tradition is an important influence, but U.S. law also includes constitutions, legislation and regulations. State and federal authority differ, and legal traditions can be mixed; the label does not supply one rule for all American disputes.

Is common law the same as statutory law?

No. Statutory law comes from legislation; common-law rules develop through decisions. Courts interpret statutes, and applicable legislation can change common-law rules, so researching a problem often requires both enacted text and cases.

Is every court decision binding precedent?

No. The relevant court hierarchy, jurisdiction, issue and holding matter. A decision can be persuasive without binding the court handling the later dispute. Current treatment must also be checked before relying on it.

Common law is most useful as a way to understand how legal rules develop, not as a shortcut around written law. For a real dispute, identify the jurisdiction, check current legislation and controlling decisions, and obtain advice about the specific facts and procedure.