By Samantha Paul Not every legal rule in the United States begins with a bill passed by a legislature. Many important principles were developed as judges decided disputes and explained the reasons for their rulings. Those accumulated decisions form what lawyers call common law, a central feature of the American legal system. It influences questions about negligence, contracts, property, and other disputes that statutes do not fully answer. Yet common law is neither an alternative to the Constitution nor a collection of rules that judges can change at will. Its authority depends on precedent, jurisdiction, and the relationship between judicial decisions and written law.
Common Law: The Basic Legal Meaning
Common law is a body of legal principles built through judicial decisions rather than established solely by legislation. U.S. courts inherited much of this tradition from English law and adapted it to American constitutional government. Published decisions explain how rules apply to actual disputes, creating guidance for later cases.
The term has a second, broader use: a “common-law system” refers to a legal tradition that gives substantial weight to prior judicial decisions. The United States has that tradition, although modern statutes and regulations govern many subjects.
That distinction explains why a rule may be described as “common law” even after a legislature has enacted related legislation. Courts may continue to use earlier case decisions to fill gaps, define legal duties, or interpret statutes, provided those decisions do not conflict with controlling written law.
How Precedent and Stare Decisis Work
Precedent is a prior decision that helps determine the result of a later case. Stare decisis—Latin for “to stand by things decided”—expresses the practice of following applicable prior rulings. The goal is consistency: similar disputes should not turn entirely on which judge happens to hear them.
Binding precedent generally comes from a higher court with authority over the court deciding the new case. For example, the U.S. Supreme Court’s holdings on federal constitutional questions bind state and federal courts. Decisions from courts in other jurisdictions may be persuasive rather than binding.
Judges compare the material facts and legal issues, not simply the titles of cases. They can distinguish a precedent when the differences matter. A court with appropriate authority can also overrule an earlier decision, but doing so is subject to institutional and legal constraints.
A trial court also needs to identify the specific legal holding of a decision. Remarks that were not necessary to reach the result, sometimes called dicta, can be informative but do not automatically have the same binding force. A later decision may clarify the boundary between the holding and background discussion.
Common Law Compared with Statutory Law
Statutory law consists of written rules enacted by Congress or a state legislature. Common law develops through case decisions. Both operate together: a statute might set a filing deadline while court decisions explain what must be proved and how ambiguous words should be interpreted.
Where valid legislation replaces a common-law rule, courts must follow the statute. Constitutional provisions take precedence over conflicting statutes and common-law doctrines. Administrative regulations may also control when issued under lawful authority.
Common law should not be confused with “civil law” as a category of noncriminal disputes. In legal-system comparisons, “civil-law systems” instead describes traditions built primarily around comprehensive codes.
Where Common Law Matters Most
Tort law offers a familiar illustration. Courts developed many rules concerning the duty to use reasonable care, causation, and recovery for injury. Contract law likewise contains judge-made principles about offers, acceptance, and remedies, although commercial statutes modify significant areas.
The 1928 New York decision in Palsgraf v. Long Island Railroad Co. is regularly studied for its competing approaches to foreseeability and negligence. It is influential, but its treatment does not automatically determine the law in every state.
Criminal law also has common-law roots, but modern American crimes and punishments are predominantly defined by statutes; the authority to punish cannot simply be assumed from an old common-law label.
State Law, Federal Law, and Historical Limits
Most American common law is state law, so two states may recognize different rules for similar disputes. Federal courts use federal common law only in limited fields involving distinctly federal interests. Under Erie Railroad Co. v. Tompkins (1938), federal courts hearing ordinary state-law claims through diversity jurisdiction generally apply state substantive law rather than inventing a general federal common law.
Because precedents can be narrowed, displaced by legislation, or overruled, legal research must check whether a case remains authoritative.
Frequently Asked Questions
Q. Can a judge rely on a decision from another state?
Yes, as persuasive authority if no controlling local decision resolves the issue. The judge must still follow binding law from courts with jurisdiction over the case.
Q. Do juries create common law?
Juries ordinarily decide disputed facts and apply the instructions given by the judge. Appellate court opinions are the main source of precedential legal rules.
Q. How can a researcher tell whether an old case is still good law?
Researchers check subsequent opinions, statutes, and citator services that flag when decisions have been criticized, distinguished, reversed, or overruled. A well-known case may be historically important without controlling today.
Q. Is common law the same as an unwritten social custom?
No. An everyday custom does not become enforceable law merely because people follow it. A court may sometimes consider custom as evidence, but a common-law rule derives its authority from recognized legal decisions.