Where does law come from? In most modern states the answer includes constitutions, statutes passed by legislatures, regulations made by government agencies, and court decisions. But countries weigh these sources differently, and comparative lawyers group legal systems into broad families that share a history and a way of reasoning.
Common law
The common law grew up in England after the Norman Conquest of 1066, as royal judges travelling the country built a body of law “common” to the whole realm. Its key feature is precedent. Under the doctrine of stare decisis (Latin for “to stand by things decided”), courts follow earlier decisions on the same legal point, and lower courts are bound by higher ones. What binds is the ratio decidendi, the legal reasoning necessary to the decision; side remarks, called obiter dicta, are only persuasive. A judge facing an awkward precedent may “distinguish” it by showing that the facts differ in an important way.
The common law spread through the British Empire and is the basis of law in England and Wales, Ireland, most of the United States, most of Canada, Australia, New Zealand, India and many other countries. Statutes are central there too, and a valid statute overrides judge-made law.
Civil law
The civil law family is the most widespread in the world, covering continental Europe, Latin America and much of Asia and Africa. Its roots lie in Roman law, especially the great compilation made under the emperor Justinian in the sixth century, which was rediscovered and taught in medieval universities such as Bologna. Its modern form comes from comprehensive codes, above all the French Civil Code of 1804 (the Napoleonic Code) and the German Civil Code, in force from 1900. In civil law systems the code is the starting point, judges reason from its general principles, and the writings of legal scholars carry great weight. Earlier decisions matter in practice, especially those of top courts, but they are not formally binding in the same way as common law precedent.
Religious and customary law
Religious law includes Islamic law, Jewish law (halakha) and Catholic canon law. In Islamic legal thought, sharia is the divine path, while fiqh is the human scholarly effort to understand it, drawing on the Quran, the example of the Prophet, scholarly consensus and reasoning by analogy. Many countries apply religious law mainly in family matters such as marriage and inheritance.
Customary law consists of unwritten practices that a community accepts as binding, often administered by elders or traditional leaders. Several African and Pacific states formally recognize it; South Africa's constitution, for example, recognizes customary law subject to the constitution and its bill of rights.
Mixed systems
Many places blend families. Scotland, South Africa, Quebec and the US state of Louisiana combine civil law roots with common law methods and are called mixed jurisdictions.
International law
International law governs relations mainly among states. There is no world legislature, so its sources are different. The Statute of the International Court of Justice, Article 38, lists treaties, international custom and the general principles of law, with judicial decisions and the writings of leading scholars as subsidiary means of finding the law. Enforcement is weaker than in domestic law and relies heavily on consent, reciprocity and reputation, yet most states follow most of their international obligations most of the time.
Worked example: one dispute, two traditions
A homeowner hires a builder to repair a roof. The builder finishes, but the roof leaks in the first heavy rain, damaging furniture. The homeowner refuses to pay the final bill, and the builder sues. How might lawyers approach the case in two traditions?
In a common law court, the homeowner's lawyer would search for earlier decisions with similar facts: cases where builders were held responsible for defects, and what the courts said about the duty to do work with reasonable skill. The builder's lawyer might argue that those precedents are distinguishable, because in this case the homeowner chose cheaper materials against advice. The judge would identify the ratio of the most relevant binding precedent and apply it, alongside any statute on consumer contracts.
In a civil law court, the lawyers would begin with the articles of the civil code on contracts for work, which set out the builder's obligations and the remedies for defective performance. They would cite leading scholarly commentaries on how those articles are understood, and point to decisions of the highest court as strong guidance. The judge would reason from the code's general rules to the facts.
The result might well be the same in both courts: the builder must fix the roof or reduce the bill. What differs is the starting point and the style of argument: in one, a chain of past cases; in the other, a structured code. In a mixed jurisdiction such as Scotland, a lawyer might draw on both habits at once.