Common law differs from Roman law in one fundamental way: common law is built case by case from judicial decisions that bind future courts, while Roman law, known today as civil law, starts from comprehensive written codes that judges apply rather than create. Everything else that separates the two traditions, from how trials run to whether a jury is ever involved, flows from that single distinction. Roughly 80 countries follow common law systems rooted in England, while more than 150 draw their legal frameworks from the Roman civil law tradition.
Where the Law Comes From
This is the biggest practical gap between the two traditions.
In a common law system, the primary source of law is judicial precedent, known as stare decisis, Latin for “to stand by things decided.” When a higher court rules on a legal question, that ruling binds lower courts facing similar facts within the same jurisdiction.1Congress.gov. Historical Background on Stare Decisis Doctrine Statutes exist and matter, but courts constantly interpret them, and those interpretations carry their own binding force. The doctrine was so central to early common law that it functioned as essentially the entire legal system during periods when legislation was rare.2Federal Judicial Center. Stare Decisis
Civil law systems flip that hierarchy. Comprehensive legal codes are the supreme authority, and judges interpret and apply those codes rather than building law through their decisions. A prior court ruling may be persuasive, and judges in practice pay attention to how other courts have read a code provision, but those rulings do not formally bind future courts the way common law precedent does. The written code remains the definitive statement of what the law is.
The historical roots match the structures. Common law grew out of England after the Norman Conquest of 1066, when royal courts gradually wove local Anglo-Saxon customs into a single body of law through accumulated judicial decisions.3Britannica. Anglo-Saxon Law4Creighton University Libraries. The Emergence of the Common Law of England Roman law took its most influential form in the 6th century AD, when Emperor Justinian I ordered the compilation of centuries of legal scholarship and imperial decrees into the Corpus Juris Civilis.5Max-EuP 2012. Corpus Juris Civilis The philosophy of writing law down comprehensively, rather than letting it emerge from individual disputes, became the defining feature of every civil law system that followed.
How Trials Are Run
Common law courts use an adversarial model. Two opposing sides gather their own evidence and present competing arguments, and the judge acts as a referee ensuring fairness and proper procedure rather than investigating the case independently.6George Mason University School of Law. Rent-Seeking Through Litigation – Adversarial and Inquisitorial Systems Compared The underlying theory is that truth emerges best from a structured contest between motivated opponents.
Civil law courts follow an inquisitorial model. The judge takes an active role in investigating the facts: ordering evidence, questioning witnesses directly, and building the factual record rather than passively receiving what two sides choose to present.7Britannica. Inquisitorial Procedure In countries like France and Germany, an investigating magistrate may spend months examining evidence before a case ever reaches trial, recommending that it proceed only when satisfied that sufficient evidence exists. Lawyers in these systems still advocate for their clients, but they work within a framework the judge controls rather than driving the process themselves.
The jury contrast follows from this. Common law systems rely heavily on juries, panels of ordinary citizens without legal training who evaluate the evidence and determine what actually happened, after which the judge applies the law to those findings. Civil law systems generally do not. The judge or a panel of judges handles both fact-finding and legal analysis, which fits the inquisitorial approach where the court itself builds the record. Some civil law countries use lay judges or mixed panels for certain serious criminal cases, but the common law concept of a standalone jury as the trier of fact is largely absent.
How Judges Reason Through Cases
The two traditions use different styles of logic, and this shapes how lawyers argue and how judges write their decisions.
Common law reasoning is primarily inductive. A judge looks at how previous courts handled similar factual situations, identifies the principles those decisions established, and reasons by analogy to determine whether the current case should follow or depart from that pattern.8Florida International University Faculty. Legal Reasoning Notes The general rule emerges from the ground up, built on the accumulated weight of specific decisions. This is why common law lawyers spend so much time researching past cases and arguing that their client’s situation is or isn’t sufficiently similar to a controlling precedent.
Civil law reasoning is primarily deductive. The judge starts with the general principle stated in the code, identifies the relevant provision, and applies it to the specific facts at hand. The logic runs from the general to the particular. A civil law lawyer’s skill is less about distinguishing prior cases and more about demonstrating how the facts fit within the code’s framework and what the drafters intended.
Contract Remedies
When someone breaks a contract, the default remedy reveals a philosophical gap between the two traditions. Common law treats monetary damages as the standard fix. A court calculates what the broken promise cost you in financial terms and orders the breaching party to pay. Specific performance, where a court orders someone to actually do what they promised, is available but treated as an exceptional remedy reserved for situations where money cannot make the injured party whole, such as sales of real estate or unique items.9Legal Information Institute (Cornell Law School). Specific Performance
Civil law systems often approach this differently. Under traditions influenced by Roman law, specific performance is frequently the primary remedy. The logic is straightforward: you agreed to do something, so the court’s first instinct is to make you do it, not to let you buy your way out. Monetary damages become the fallback when performance is truly impossible or impractical. German law treats specific performance as the general remedy for breach, with damages available when performance fails.
What a Notary Does
A small but telling difference involves notaries. In common law countries like the United States, a notary public is a relatively minor official who verifies identities, witnesses signatures, and administers oaths. In civil law countries, a notary is a highly trained legal professional who drafts contracts, provides legal advice, conducts due diligence on the parties involved, and authenticates documents so they carry near-judicial weight. Civil law notaries serve as preventive legal gatekeepers, ensuring transactions are legally sound before they happen, which reduces the need for litigation after the fact.
Where Each System Is Used
Common law systems dominate in countries with historical ties to the British Empire. The United Kingdom (except Scotland), the United States (except Louisiana), Canada (except Quebec), Australia, and New Zealand all operate under common law traditions.10JuriGlobe. Common Law Systems and Mixed Systems With a Common Law Tradition India uses common law blended with customary and religious law traditions. Civil law systems span continental Europe, Latin America, and large portions of Asia and Africa, reflecting the influence of the Napoleonic Code and other post-Roman codifications.
The exceptions within those lists matter. Scotland blends civil law with common law. Louisiana’s private law is rooted in the French civil tradition, but its public law follows American common law patterns. Quebec’s civil code governs private matters while Canadian common law handles everything else.11Loyola Law Review. The Mixite of Quebec’s Recodified Civil Law Puerto Rico operates under a similar hybrid, with Spanish civil law foundations governing areas like family law and property while American common law applies to constitutional and federal matters. The two traditions have also been quietly borrowing from each other for decades, with common law countries relying more on comprehensive statutes and civil law courts treating established lines of interpretation as practically binding. The core difference, whether judges primarily follow prior rulings or apply written codes, remains the most reliable way to tell the traditions apart.