Two friends, one in Texas and one in Mexico City, each sign a lease. Each assumes that if the landlord cheats, a court will sort it out. Both are right. But the Texan's lawyer will go looking for earlier court decisions about leases like this one, while the lawyer in Mexico City will open a code and look for the article that governs the case, and then for how the highest courts have read that article. Neither lawyer is being quirky. They were taught in different traditions.
Travel a few hours further and the picture shifts again. In Berlin a student becomes a lawyer only after two state exams and two years of supervised training. In Riyadh a judge may rest a ruling on a scholarly tradition of reading the Qur'an and the Prophet's example. In Johannesburg a court applies a 1996 constitution, an English-flavoured procedure and a private law that traces back to Roman-Dutch authors. Same planet, same human troubles, different machinery.
This piece is the map. It does not teach you to practise anywhere. It shows the common ground first, then the main families, then how each trains its lawyers. It describes how legal systems work; it is not legal advice, and laws differ by country and change.
Strip away the Latin and the wigs and every legal system is answering the same five questions. Promises: when will the community force you to keep one? Harm: when must you pay for the damage you cause? Ownership: who holds a thing, and how can everyone else tell? Crime: which wrongs are the community's business, and how is guilt decided fairly? Power: what may rulers do, and who can stop them?
Notice that these are human problems, not legal ones. A village of forty people has them. What law adds is a way to answer them in advance, in writing or in remembered precedent, so that strangers can rely on the answer. The families differ in where they write the answer down and who is trusted to apply it, much more than in what they want to achieve.
Simplified on purpose. "Latin America" means the civil-law codes of Mexico, Argentina, Brazil, Chile and Colombia, which differ among themselves; "continental Europe" means mainly France, Germany and Spain. The EU adds a layer on top (see 35/11).
Read the promise row. The US asks whether something was bargained for (consideration). Chile's code, in the Bello tradition, asks for a lawful cause. France dropped "cause" as a separate requirement in its 2016 reform of the law of obligations; Germany never needed either word and leans on good faith. Four ways of drawing the line between a gift you cannot enforce and a deal you can. We return to this in Contracts & Obligations (35/04).
A source of law is anything a court will accept as a reason. Every system has a stack of them: a constitution on top, then (where relevant) treaties, then statutes or codes, then regulations made under them, then court decisions, scholarship and custom. What differs is how heavily a lawyer leans on each rung.
In the common-law tradition, which began in medieval England and spread to the United States, Canada, Australia, India and much of Africa, judges built large parts of the law case by case: contract, tort and property rules are still found mainly in decisions. Statutes now sit above them and can override them, but a lawyer starts by asking what courts have said. In the civil-law tradition, which grew from Roman law through the medieval universities and then the great codes, the starting point is a code or statute, and decisions illustrate how to apply it. Professors' commentaries matter more than in the US because the code is short and general.
Illustrative scores from 0 (rarely cited) to 4 (the first thing a lawyer reaches for), written by the author to show a pattern, not measured. Real weights vary by field: US contract law leans on cases, but the Uniform Commercial Code is a statute.
The honest picture is convergence. Common-law countries now run on statutes (tax, criminal law, consumer law, the US Constitution itself). Civil-law countries now run on precedent in practice: constitutional courts, and in Latin America the supreme courts, issue rulings that lower judges ignore at their peril. Lawyers in either family now read both kinds of source. The difference is the default, which is the thing a first-year student has to unlearn when she crosses the border.
The civil-law family begins with Rome. In the 530s the Eastern Roman emperor Justinian had his lawyers compile centuries of Roman jurists' writings and imperial rulings into what later ages called the Corpus Juris Civilis: a Code (first issued 529, revised 534), a Digest of the jurists and a textbook, the Institutes (both 533). It was rediscovered and taught at Bologna from about 1100, and for centuries it was the shared legal language of Europe's universities.
The second step was the code: a single, organised statute for a whole area of law, written for citizens as well as lawyers. France's Code civil of 1804 (the "Napoleonic Code") was the model for much of the world. Germany's Bürgerliches Gesetzbuch (BGB) entered into force on 1 January 1900 and was more abstract and technical; it influenced Japan, South Korea and others. Latin America took its own routes. Andrés Bello's Chilean Civil Code (enacted 1855, in force 1857) was adopted, with changes, by several neighbours including Colombia and Ecuador. Argentina's code by Dalmacio Vélez Sarsfield came into force in 1871 and was replaced by the new Civil and Commercial Code in 2015. Brazil's first Civil Code dates from 1916 (in force 1917) and its current one from 2002. Mexico's federal Civil Code was issued in 1928 and took effect in 1932, with each state also having its own.
"In force" counts from the year the code took effect, not the year it was enacted. Justinian's collection was a compilation, not a code in the modern sense.
Notice what a code changes. Before 1804 a French lawyer faced hundreds of local customs plus Roman law; after it, one text. That unity was the point: one citizen, one law. It also explains the civil-law suspicion of judge-made rules. Article 5 of the French Civil Code, still in force, forbids judges from deciding cases by laying down general rules. The legislature speaks; the judge applies.
In the common-law world a decision does two jobs: it settles the case, and its reasoning (the ratio decidendi) binds later courts below it in the same system. This is stare decisis, "stand by what has been decided". A US federal court of appeals must follow the Supreme Court; the Supreme Court is not absolutely bound by its own past, and does overrule itself. Brown v. Board of Education (1954) abandoned the "separate but equal" rule of Plessy v. Ferguson (1896) for public schools, and Dobbs v. Jackson Women's Health Organization (2022) overruled Roe v. Wade (1973). Precedent is strong, not absolute.
In classic civil-law theory, a judgment binds only the parties. Prior decisions are persuasive evidence of what the code means. In practice, a line of consistent rulings from a high court (French jurisprudence constante) steers lower courts, and some countries have made that explicit. Brazil's Constitution lets the Supreme Federal Court issue súmulas vinculantes, binding summaries of settled constitutional questions, by a two-thirds vote of its ministers (a rule added in 2004). Mexico's system lets certain lines of Supreme Court rulings, called jurisprudencia, bind lower courts. The EU's Court of Justice interprets EU law for all member states, whichever family they belong to.
A useful rule of thumb: in a common-law case, ask "what did the last court say about facts like mine?"; in a civil-law case, ask "what does the article say, and how have the highest courts read it?" The two questions meet in the middle more often than the textbooks admit. We practise both in Legal Reasoning & Writing (35/02).
Common and civil law are the two largest families, but they are not the whole map, and they are not tidy. Three more things sit alongside them.
Religious law. In Islamic law the sources are the Qur'an, the example of the Prophet (sunna) and the work of jurists (fiqh), organised in several schools of jurisprudence. Few states apply it as an uncodified whole today. Egypt's civil code of 1948, for example, was drafted on largely civil-law lines, while its constitution names the principles of Islamic law as the main source of legislation and family law draws on Islamic jurisprudence. Saudi Arabia's 1992 Basic Law names the Qur'an and the Sunna as its constitution and its courts have historically applied uncodified fiqh, though the state has recently been issuing written codes. Canon law governs the Catholic Church internally; Jewish halakha guides religious courts and, in Israel, shapes personal status law; Hindu, Muslim and other communities in India have their own personal laws for family matters.
Customary law. Across Africa, the Pacific and among Indigenous peoples in the Americas, unwritten community rules about land, marriage and dispute resolution still operate alongside the state's law. Several constitutions, including South Africa's, recognise customary law, subject to the constitution's rights. It is law in the full sense: it is applied by recognised authorities and has real consequences.
Mixed systems. Many places combined traditions. Scotland has civilian roots with strong common-law influence. South Africa's private law grew from Roman-Dutch authors and has English-style procedure and, since 1996, a constitution with a Constitutional Court. Louisiana's private law descends from French and Spanish civil law inside a common-law country. Quebec's Civil Code (the current one in force since 1994) governs private law while its public law follows the common-law model. Japan took French and then German codes and added American-style constitutional review after 1947.
Short labels only: every real system is a blend. Check a current source before relying on any entry.
You can tell a family by its classroom. In the US, law is a graduate degree: four years of any bachelor's degree, then three years for a Juris Doctor, then a state bar exam. Law school teaches by the case method, with Socratic questioning about decisions. In England and Wales you can read law at university or take any degree, and since the Solicitors Qualifying Examination began in autumn 2021 a would-be solicitor passes two exam stages and completes two years of qualifying work experience.
On the continent, law is an undergraduate degree, taught from the code and the commentaries. Germany's route is the classic: about four and a half years of study (nine semesters is the standard span) and a first state exam, then two years of supervised training, then a second state exam. Spain requires a law degree, a professional master's and a state exam before one can practise as an abogado. Latin American countries typically offer a five-year degree (licenciatura or abogacía), then a professional title and registration; Brazil adds the OAB bar exam, and Chile adds a supervised practice period before the Supreme Court grants the title. Mexico requires a professional licence (cédula profesional) but has no general bar exam.
Typical, rounded years under current rules as the author understands them. Individual routes vary by university, by year and by whether you work part-time; this is an illustration of structure, not a guide to qualifying.
Every society has to answer the same five questions: promises, harm, ownership, crime and power. The families differ mostly in where the answer is written (cases or codes) and who is trusted to apply it. Most real systems blend, and a lawyer's first skill is knowing which source carries the weight where she is standing.
Try this: pick a country you care about and look up whether it is common law, civil law or mixed. Then find one thing a court there decided in the last year and ask whether the judges quoted earlier cases, an article of a code, or both.
Sources. Legal families, Justinian's compilations (Code 529, revised 534; Digest and Institutes 533), the French Code civil (1804) and its article 5, the BGB (in force 1 January 1900), Bello's Chilean code and its adoption elsewhere, Vélez Sarsfield's Argentine code, Brazil's codes of 1916 and 2002, Mexico's Federal Civil Code (1928, in force 1932) and Louisiana, Quebec, Scotland and South Africa as mixed systems: Merryman and Pérez-Perdomo, The Civil Law Tradition; Zweigert and Kötz; Wikipedia's "Civil law (legal system)" as a cross-check. Brazil's Constitution, art. 103-A (binding summaries, two-thirds of the Supreme Federal Court's members, added by Amendment 45 of 2004). SQE: Solicitors Regulation Authority and Wikipedia ("Solicitors Qualifying Examination": in effect from autumn 2021; two years' qualifying work experience). Court dates: Brown 1954, Plessy 1896, Dobbs 2022, Roe 1973. Education routes are summarised from national rules and are approximate. This piece describes how legal systems work and is not legal advice.