What is law? Where laws come from and what they do

Law is a system of rules that a society recognizes as binding, made and applied by its institutions, such as legislatures and courts, and backed by the power to enforce them. What sets it apart from morality, custom or the rules of a club is that it has official sources, official judges of what it means, and official consequences for breaking it. Its job is to settle disputes peacefully, keep order, protect rights and limit power.

In short

• Law comes from several sources: constitutions, statutes passed by legislatures, decisions of courts, regulations, custom, religious texts and treaties.
• It splits into kinds that work differently: public and private, criminal and civil, domestic and international.
• The rule of law means that everyone, the government included, is bound by public rules applied by independent courts.

Not legal advice

This note explains general principles found in many legal systems. Laws differ from country to country, and nothing here is advice about any particular situation; for that, ask a qualified lawyer where you live.

What makes a rule a law?

A rule is a law when the institutions a society recognizes say it is, and stand ready to apply it. "Don't lie" is a moral rule; "don't lie under oath" is also a law, because a statute makes perjury a crime and a court can punish it. The philosopher H. L. A. Hart, in The Concept of Law (1961), put it this way: a legal system joins rules that tell people what to do with rules about the rules, saying who can make, change and apply them. That second layer is what lets a court say, with authority, which rules count.

Law is old. The Code of Hammurabi, carved in cuneiform in Babylon around 1750 BC, set out 282 laws on matters from theft to wages, with fixed penalties. Rome's Twelve Tables, around 450 BC, were displayed publicly so citizens could know the rules they lived under. That idea, that law should be written down and known in advance, runs through everything that follows.

Where do laws come from?

Most legal systems draw on the same handful of sources, ranked so that the higher one wins when two conflict:

Source	What it is	Example
Constitution	The founding law that sets up government and limits it	[[what-is-the-us-constitution
Statutes	Laws passed by a legislature	A national road traffic act
Regulations	Detailed rules made by government agencies under a statute's authority	Vehicle safety standards
Case law	Courts' decisions, which in some systems bind later courts	A supreme court ruling on what a statute means
Custom	Long-standing practice accepted as binding	Customary land rights in many African and Pacific countries
Religious law	Rules drawn from sacred texts and their scholars	Islamic law (sharia) in family matters in some countries
Treaties and international law	Agreements between states, and accepted state practice	The Geneva Conventions

How much weight each one carries depends on the legal tradition. In common law countries such as England and the United States, judges' decisions are a main source of law in their own right; in civil law countries such as France and Germany, the written codes come first. The two traditions are compared in common law vs civil law. Between countries, the Statute of the International Court of Justice lists the sources of international law in its Article 38: treaties, "international custom, as evidence of a general practice accepted as law", general principles of law, and, as a subsidiary means, court decisions and the writings of leading scholars.

What are the main kinds of law?

Law is divided in several overlapping ways, and the divisions matter, because they decide who brings a case, what has to be proved and what can happen at the end:

Division	One side	The other side
Who it governs	Public law: the state and its relations with people (constitutional, administrative, criminal, tax)	Private law: relations between private parties (contract, property, family, torts, which are civil wrongs that cause harm)
What it does	Criminal law: the state prosecutes wrongs against society and can punish	Civil law in this sense: one party sues another, usually for money or an order
Where it applies	Domestic law: within one country	International law: between states, and increasingly over individuals

The word "civil" is a trap here: it can mean non-criminal law, as in this table, or the code-based legal tradition of continental Europe, which is something else.

One accident, four kinds of law

Take one event, step by step. A driver who has been drinking runs a red light and hits a delivery van, injuring its driver.

1. Criminal law. The state, not the injured driver, prosecutes the drunk driver for driving under the influence. To convict, it must prove guilt beyond a reasonable doubt. The penalty can be a fine or prison.
2. Civil law (torts). The van driver sues for medical bills and lost wages. Here the standard is lower: in the United States, a "preponderance of the evidence", meaning more likely than not; in England, "the balance of probabilities". The remedy is money, not punishment.
3. Contract law. Both drivers' insurers pay out, or refuse to, according to the terms of their policies.
4. Administrative law. A licensing agency suspends the drunk driver's license, through its own procedure and with its own right of appeal.

The difference in standards of proof is not theoretical. In 1995 a Los Angeles jury acquitted the former football player O. J. Simpson of murdering Nicole Brown Simpson and Ron Goldman; in 1997 a civil jury found him liable for their deaths and awarded $33.5 million in damages. The same facts can fail the criminal standard and pass the civil one.

What is the rule of law?

The rule of law is the principle that power is exercised through law rather than at the whim of whoever holds it. The United Nations states it as "a principle of governance in which all persons, institutions and entities, public and private, including the State itself, are accountable to laws that are publicly promulgated, equally enforced and independently adjudicated". Its roots in English law go back to the Magna Carta of 1215, which promised that the king would act against free men only by "the law of the land", and to the writ of habeas corpus, which makes a jailer justify a detention before a judge.

The American legal philosopher Lon Fuller gave a useful checklist in The Morality of Law (1964). A system of rules fails as law, he argued, to the degree that its rules are not:

1. general, applying to classes of people rather than named individuals;
2. public, so people can know them;
3. prospective, not punishing what was legal when it was done;
4. clear enough to follow;
5. consistent, not demanding contradictory things;
6. possible to obey;
7. stable enough to plan around;
8. applied by officials as written.

A law kept secret, or one that changes weekly, or one officials ignore, fails that test even if it was properly passed.

Does an unjust law still count as law?

This is one of the oldest questions in legal philosophy, and it divides two schools.

Still argued

Natural law theorists hold that law must answer to a higher moral standard, and that a rule which badly violates it is not truly law. The idea runs from Cicero through Thomas Aquinas, and in 1963 Martin Luther King Jr. drew on it in his Letter from Birmingham Jail: "I would agree with St. Augustine that 'an unjust law is no law at all.'" Legal positivists hold that what the law is and what it ought to be are separate questions. John Austin put it in 1832: "The existence of law is one thing; its merit and demerit another." Hart defended that view, arguing that calling an evil law "not law" muddies the moral question of whether to obey it. The two positions met head-on in 1958, when Hart and Fuller debated in the Harvard Law Review how courts should treat laws made under the Nazis. Hart himself held that a rule could be valid law and still too wicked to obey, so the disagreement is less about obedience than about whether calling such rules "law" is accurate, and whether it matters.

The question is practical, not only academic. After the Second World War, the Nuremberg trials had to answer defendants who said they had obeyed the laws of their state. And modern constitutions answer part of it by writing moral limits into law itself, as bills of rights and human rights treaties do, so that a statute breaking them can be struck down by a court.

How do legal systems differ around the world?

Every country mixes the sources above in its own way, but most belong to a few families: the common law of England and its former colonies; the civil law of continental Europe, Latin America and much of Asia; religious law, chiefly Islamic law in some countries' family and criminal law; and customary law, especially in parts of Africa and the Pacific. Many are mixed: Scotland, South Africa, Quebec and Louisiana combine common and civil law. Within each, law reaches from crimes to copyright, and it changes as legislatures pass new rules, a process traced in how a bill becomes a law.

Check yourself

• Without looking, name four sources of law and say which one usually wins when they conflict.
• Why could the same person be acquitted of a crime and still be found liable in a civil case for the same act?
• What is the difference between the natural law and the positivist answer to "is an unjust law still law"?

Sources

• Legal Positivism — Stanford Encyclopedia of Philosophy
• The Rule of Law — Stanford Encyclopedia of Philosophy
• What is the Rule of Law — United Nations and the Rule of Law
• Statute of the International Court of Justice — International Court of Justice
• Letter from a Birmingham Jail — Martin Luther King Jr., 1963, African Studies Center, University of Pennsylvania
• The Code of Hammurabi, translated by L. W. King — The Avalon Project, Yale Law School