What Is Common Law?
By the BrainSnail editorial team. How these articles are written and checked, and how to tell us when one is wrong.
Common law is a legal system in which law develops through the decisions of judges in individual cases, with each decision binding future courts. It grew out of medieval England and now underpins the legal systems of a large part of the world, standing alongside the very different civil law tradition.
Built from precedent
Common law is built from precedent. When a court decides a case, the legal reasoning behind that decision becomes binding on lower courts facing similar facts. Over time, an enormous body of law accumulates from decided cases rather than from a single written code.
The formal principle is stare decisis, meaning to stand by things decided. It gives the system predictability, because parties can look at how similar disputes were resolved and anticipate the outcome.
Where it came from
The name comes from the effort after the Norman conquest to establish law common to the whole of England rather than varying by locality. Royal judges travelled the country deciding cases, and their decisions were recorded and reused.
The system spread with British influence, which is why it now operates in the United States, Canada, Australia, India, Nigeria and many other countries. Each has developed its own body of precedent, though courts still sometimes look to decisions from other common law jurisdictions as persuasive.
How it differs from civil law
Most of continental Europe, Latin America and much of Asia use civil law systems, descended from Roman law and reorganised by the Napoleonic and German codes.
The differences are real though often overstated:
- •Civil law starts from a comprehensive written code rather than case decisions
- •Civil law judges are less bound by previous rulings
- •Common law trials are adversarial, with parties driving the case
- •Civil law proceedings are more inquisitorial, with judges investigating actively
How precedent actually works
Not everything in a judgment binds future courts. Only the reasoning essential to the decision, the ratio decidendi, is binding. Other observations, however interesting, are persuasive at most.
Courts also have room to move. A judge can distinguish a precedent by identifying a material factual difference, and higher courts can overrule earlier decisions outright. This is what stops the system from being frozen by decisions made in very different circumstances.
Statute and common law together
No modern common law country runs on precedent alone. Legislatures pass statutes constantly, and where a statute conflicts with common law, the statute wins.
What remains distinctively common law is the interpretive role. Courts decide what statutory words mean in practice, and those interpretations then become precedents themselves. Large areas such as contract and negligence still rest primarily on case law built over centuries.
Why judgments are written the way they are
Common law judgments are long, discursive and often include disagreement, which surprises people used to the short declaratory rulings of civil law courts.
The length has a function. Because the reasoning becomes binding on future courts, judges must set out exactly which facts mattered and why, so later courts can apply or distinguish it. Dissenting opinions are published too, and dissents have occasionally become the majority view decades later, which means preserving the losing argument has real value in a system built on accumulated reasoning.
The takeaway
Common law develops through binding judicial decisions rather than a single written code, it spread from England across much of the world, and it now operates alongside statute with courts shaping how legislation is applied.