Law is a system of rules that regulates the conduct of a community and is enforced by a controlling authority. Law is usually embodied in an enforceable contract, in the form of a statute or an ordinance, or by a case ruled on by a judge or jury. An important branch of law is criminal law, which deals with offenses against the state and its agencies. Other important branches of law include torts, which deal with injuries to people or their property; bankruptcy, which restructures the debts of businesses; labor law, which covers employment relationships between employers and employees; family law, which addresses divorce proceedings and the rights of children; real estate law and corporate law.
Legal systems vary from country to country. Some, such as the United States, use a common law system in which laws are developed from judicial decisions based on the facts of each case; these decisions are collected into legal books called case law. Other countries, such as Japan, have a civil law system in which laws are embodied in written codes that explicitly specify what judges must do to arrive at a ruling in each case.
The development of law has not always been logical. The felt necessities of a particular age, the prevailing moral and political theories, and intuitions of public policy, whether avowed or unconscious, have had much to do with determining the laws by which men should be governed.
In the 17th century, Edward Coke, a Lord Chief Justice of England and member of parliament, wrote several legal texts that collected and integrated centuries of case law into what became known as common law. He used ancient maxims, such as “He who seeks justice must not expect it of himself” and “one cannot be a judge in his own cause,” to formulate what was then considered sound reasoning. Many of these maxims still serve as guiding principles of common law today.