Law is the system of rules a nation or community recognizes as regulating its members’ actions. It encompasses all the institutions and procedures that are used by governments to uphold rights, settle disputes, protect people from abuses of public power, and govern social change. It is also the body of rules that a legal system must be able to produce and enforce. The precise definition of law is a matter of longstanding debate.

One view, associated with Holmes, defines it as the body of norms that are promulgated so that people can study and internalize them, and use them to guide their actions, plan expectations, and settle disputes. This ontology, or epistemology, of law requires that the laws be open and relatively stable and that they operate impersonally and without bias.

Another approach is based on moral considerations and argues that the proper purpose of law is to serve the common good. It is a view that was popularized by Cicero and St Augustine of Hippo. It holds that positive law is valid only if its makers are motivated by the care of the common good; otherwise it is invalid. This principle is known as the Rule of Law, and it has been a central theme of debates about law for centuries.

In practice, the definition of law varies widely across nations and communities. It is influenced by the political history and culture of the region, the economic structure of society, and the way in which people perceive the purpose and function of law. The most important consideration is who has the power to make and enforce law, since this determines whether the basic functions of law are served. In a democracy, the legislature makes the law; in authoritarian regimes, the executive branch of government carries out this role. In either case, the political landscape is vastly different from one country to the next. This reality makes it very difficult to generalize about what constitutes a ‘law’. Some legal pragmatists (like Posner) argue that it is better to trust judges’ insight into new situations than to rely on strained analogies with ancient precedents.