Law is a system of rules enforced by a sovereign government to regulate social and private behaviour. Its precise nature has been debated for centuries, with many commentators describing it as both a science and an art. The principal purposes of law are to establish standards, maintain order, resolve disputes and protect liberties and rights. The governing bodies of most states have a variety of tools to exercise this power, ranging from legislative instruments such as bills and regulations to judicial decision-making and executive orders. In addition, governments have a range of specialised agencies and departments to control specific aspects of public life. These may include the military, police and civil service. The latter have the power to monitor, punish and prosecute citizens and are therefore a powerful form of control.
Modern societies are governed by a complex mix of laws, with some countries using a mixture of constitutional, common and civil law systems. Most western countries have a legal system that combines elements of common law with statutory law, while some, such as Japan, use a purely constitutional law approach. Other nations have a civil law tradition that is based on categories, concepts and rules derived from Roman law and canon law, often supplemented or modified by local custom.
The term law encompasses many types of regulations, but some of the most prominent are contract law, property law, and criminal law. Contract law governs agreements to exchange goods or services and can cover everything from buying a bus ticket to trading options on a derivatives market. Property law establishes people’s rights and duties toward tangible objects such as houses and cars, and intangible assets like bank accounts and shares of stock. Criminal law defines the actions that are considered a crime and how they are punished, but there is also civil liability for some crimes.
Whether a society uses a common law, civil or constitutional system, it can be difficult to empirically verify the contents of its law. It is impossible for any human being to observe the entire universe and determine what should be deemed right or wrong in all circumstances. Nevertheless, there are certain universal principles that can be applied to any situation.
A major part of the law in any given jurisdiction depends on a judge’s interpretation of a case and is largely dependent on the decisions of judges in other cases that have been tried previously. The earliest English legal authority, Sir William Blackstone, referred to judges as “the living oracles who must decide in all doubtful cases.” However, Blackstone also wrote that a ruling should not be followed if it was “clearly contrary to reason and the law of God.” This principle is the basis for the doctrine of precedent. Other important legal principles include agency and insurance law, air and carriage of goods law, bills of exchange, bankruptcy and insolvency law, and commercial law derived from the medieval Lex Mercatoria and the UK Sale of Goods Act.