Common law and precedent are related in a direct, mechanical way: precedent is how common law is made. When a judge decides a case and explains the reasoning, that decision becomes a reference point for later courts facing similar questions. Stack those reference points across decades, and the accumulated body of rulings is common law. Precedent isn’t a supplement to common law; it is the tool that builds it and the doctrine of stare decisis is what holds the whole structure together.
Common Law in One Paragraph
Common law is law that comes from court decisions rather than from statutes passed by a legislature. When a judge rules and explains why, that reasoning carries weight beyond the parties in the courtroom. Over time, those rulings accumulate into legal principles that courts treat as authoritative. It is often called “judge-made law,” and that is exactly what it is: rules built case by case. Common law fills the enormous space where no statute exists. Legislatures cannot anticipate every possible dispute, so courts develop rules for situations statutory law does not cover, and those rules evolve as new facts arise. A rule developed for horse-drawn carriages can be adapted for automobiles and later for autonomous vehicles, all through the same process. That adaptability works only because courts do not start over each time. They build on what came before.
What Precedent Is
A precedent is a court decision that serves as authority for resolving a similar legal question later. Two distinctions inside that idea do most of the work.
Binding Versus Persuasive Authority
Binding precedent comes from a higher court in the same jurisdiction, and lower courts must follow it. A U.S. Supreme Court decision on federal law or the Constitution binds every federal and state court in the country.1Constitution Annotated. Supreme Court Review of State Court Interpretations of Federal Law A federal circuit court’s decisions bind the district courts within that circuit. A state supreme court’s rulings bind every lower court in that state.
Persuasive authority is a decision a court may consider but is not obligated to follow. Rulings from courts in other states, from lower courts, or from courts at the same level fall into this category. A trial court in Ohio might find a well-reasoned opinion from a Virginia appeals court useful on a novel question, but nothing forces it to follow that opinion. Legal treatises and the Restatements of the Law published by the American Law Institute also function as persuasive authority where binding precedent does not exist.
Holding Versus Dicta
Not everything in a judicial opinion is binding. Only the holding is. The holding is the part of the decision necessary to resolve the actual dispute, the legal principle the court had to reach to decide who wins and who loses. Everything else, including side observations, hypothetical musings, and commentary on issues that were not at stake, is called obiter dicta, usually just “dicta.” Dicta is not binding on any court, though it can be persuasive when it comes from an influential court or a respected judge. Dissenting opinions are generally treated as dicta too. Much of legal argument turns on whether a particular passage in an opinion is holding or dicta, because that classification determines whether a later court has to follow it.
Stare Decisis: The Doctrine That Ties Them Together
The formal doctrine connecting precedent to common law is stare decisis, Latin for “to stand by things decided.” It is the principle that once a court resolves a legal question, future courts should follow that resolution rather than reinvent the answer. Without stare decisis, precedent would be optional guidance rather than a structural feature of the legal system, and common law as it exists would not.
The doctrine serves several purposes at once. It makes law predictable, so people and businesses can plan with some confidence about legal consequences. It promotes fairness by treating similar cases the same way. And it preserves public confidence in the judiciary by keeping outcomes from swinging on which judge hears a case.
Vertical and Horizontal Stare Decisis
Stare decisis runs in two directions. Vertical stare decisis is the straightforward one: lower courts must follow the decisions of higher courts in the same chain of authority. A federal district court in California is bound by Ninth Circuit precedent. The Ninth Circuit is bound by the U.S. Supreme Court. A state trial court is bound by its state appellate courts and state supreme court. Ignoring binding precedent from above almost guarantees reversal on appeal.1Constitution Annotated. Supreme Court Review of State Court Interpretations of Federal Law
Horizontal stare decisis is looser. It refers to a court’s practice of following its own prior decisions. The Supreme Court generally adheres to its past rulings but has the power to overturn them. Lower appellate courts sometimes revisit their own precedent as well, though cautiously. Horizontal stare decisis is a strong presumption rather than an absolute command, and that flexibility is what lets common law correct its own mistakes over time.
How Precedent Actually Builds Common Law
The relationship is easiest to see when you trace a legal concept across a chain of cases. Negligence is the clearest example. Early English courts did not recognize negligence as a distinct basis for liability. If someone harmed you, the question was usually whether the act was a direct trespass, not whether the person had been careless.
That changed through individual decisions. In the 1928 case Palsgraf v. Long Island Railroad, New York’s highest court addressed who can sue for injuries caused by another’s carelessness. Chief Judge Cardozo’s opinion established that a duty of care exists only toward people within the foreseeable zone of danger, not to the world at large. That holding became binding precedent in New York and persuasive authority everywhere else, and it shaped how American courts think about negligence.
Later cases built on that foundation. One decision applied the duty of care to medical professionals, another to product manufacturers, another to property owners hosting visitors. Each ruling created a new, more specific precedent. Over time, the accumulation produced the body of negligence law that exists today, covering what counts as a “reasonable” standard of care, how far the duty extends, and whether harm was a foreseeable result of the defendant’s conduct. No legislature wrote that body of law. Courts built it, precedent by precedent.
When Precedent Does Not Control the Outcome
Precedent is the backbone of common law, but it does not always dictate the result. Two situations recur.
Distinguishing Cases
When a party faces unfavorable precedent, the most common strategy is to distinguish the earlier case. The argument is that the facts or legal context of the current dispute are meaningfully different from the precedent, so the earlier ruling should not apply. If the court agrees the factual differences are legally significant, it can reach a different conclusion without overturning the original precedent. The earlier case remains good law; it just does not govern the situation at hand. The opposite move is equally common: when favorable precedent exists, a lawyer argues the facts are closely analogous and the same rule should apply. Both moves show how central precedent is to the system.
Cases of First Impression
Sometimes a court faces a legal question no court in its jurisdiction has previously decided. These are cases of first impression, and they are where new common law gets created most visibly. With no binding precedent, the court reasons from broader legal principles, looks to persuasive authority from other jurisdictions, and applies its best judgment about how the law should develop. The resulting opinion becomes the first precedent on that issue. Cases involving new technology are frequent examples; the first time a court had to decide whether email communications could form a binding contract, it was working without directly applicable precedent.
When Courts Overturn Their Own Precedent
Stare decisis is a strong presumption, not an unbreakable rule. Courts can and do overturn prior decisions, though the bar is deliberately high. The party asking a court to abandon precedent carries a heavy burden and must show a special justification beyond simply arguing the earlier case was wrongly decided.2United States Court of Appeals for the Armed Forces. Miscellaneous Matters – Judicial Review – Stare Decisis
Courts weighing whether to overturn precedent generally consider whether the prior decision has proven unworkable in practice, whether later legal developments have undermined its reasoning, whether people and institutions have built their affairs around the existing rule, and whether overturning it would damage public confidence in the stability of the law.2United States Court of Appeals for the Armed Forces. Miscellaneous Matters – Judicial Review – Stare Decisis Reliance interests often matter most. When people have organized their lives around a rule, courts are reluctant to pull it out from under them even if the original reasoning was questionable.
The best-known example is Brown v. Board of Education, in which the Supreme Court in 1954 unanimously declared that racial segregation in public schools violated the Fourteenth Amendment. The Court explicitly rejected the “separate but equal” doctrine that had stood since Plessy v. Ferguson in 1896, holding that “in the field of public education the doctrine of ‘separate but equal’ has no place” and that “separate educational facilities are inherently unequal.”3National Archives. Brown v. Board of Education (1954) Brown shows both the power and the limits of stare decisis. Plessy survived nearly sixty years before the Court concluded it was fundamentally wrong. The bias toward stability lets bad precedent persist, but the ability to overturn it means common law can eventually self-correct.
The Limit: Statutes Can Displace Common Law
Common law does not exist in isolation. Legislatures can pass statutes that replace, modify, or codify common law rules, and when a statute directly addresses a subject previously governed only by court decisions, the statute controls. Courts presume, though, that legislatures do not intend to displace common law unless they say so clearly. If a statute uses a term with an established common law meaning, courts generally interpret it according to that common law definition. When a statute covers a topic previously governed by common law, the default assumption is that the legislature intended to keep the substance of the common law intact unless it clearly indicated otherwise.4Congress.gov. Statutory Interpretation – Theories, Tools, and Trends A party arguing that a new statute changed settled common law bears the burden of proving the legislature intended the change. The Uniform Commercial Code works this way in practice: it replaced many common law rules on the sale of goods with standardized statutory provisions, but it also states that common law principles of contract continue to supplement its provisions wherever the UCC does not specifically displace them.
The takeaway for anyone reading a court opinion, negotiating a contract, or trying to make sense of a legal problem is that huge areas of American law, including contract principles, property rules, and tort liability, still rest primarily on judge-made common law built through precedent. When a lawyer says “the case law supports our position,” that is the relationship at work: prior decisions, accumulated through precedent and held in place by stare decisis, forming a body of common law that governs the situation in front of you.