Law is a set of rules created and enforced through social or governmental institutions to regulate behaviour. Its precise definition is a subject of long-standing debate. Some see law as an instrument of justice; others regard it as a system that ensures order and protects against government or private abuse of power. Its scope extends into virtually every aspect of life. Its three main subjects are presented below for convenience, though they often intertwine and overlap:

Contract law covers agreements to exchange goods or services; property law defines people’s rights and duties toward tangible assets like land or cars; and criminal law concerns what a citizen can or cannot do within a governed society. The law also governs the relations between different parts of a society: labour law refers to the tripartite industrial relationship between employee, employer and trade union; public and administrative law deals with a country’s management of its infrastructure such as energy, water, telecomms and transport; while civil procedure and evidence law concern the rules that courts must follow as trials and appeals proceed.

The most fundamental requirement of law is that it be public, both in the sense of actual promulgation and in the sense of accessibility and intelligibility. The former involves the formal requirement that laws should be clear and accessible so that ordinary citizens can study them, internalize them, figure out what they require of them, and use them as a framework for their plans and expectations and for settling disputes with others. The latter requires legal institutions and procedures that are independent, accountable, transparent and impartial.

A second principle of law is that it should be general rather than aimed at particular individuals. This reflects a desire to avoid invidious discrimination, but it is a problem because the facts about individuals’ lives and their social environments are constantly changing. This is reflected in the fact that, even when laws are formally general in character, they can often seem to target individuals.

A third principle of law is that it should be enforceable. This is a problem because, in many places, the most powerful actors are not the institutions of the state. A number of important philosophies have tried to resolve this dilemma: the legacy of Aristotle and medieval thinkers who sought to distinguish lawful from despotic kingship; the European Enlightenment’s debate about natural right theory; and American constitutionalism in the Federalist Papers and (oddly) Niccolo Machiavelli. More recently, Max Weber and others have reshaped thinking on the extension of the state, showing that modern military, police and bureaucratic power raises new problems for accountability that earlier writers such as John Locke and Montesquieu could not have imagined. This has prompted a shift to more pragmatic ideas about the nature of law. This is embodied in the work of legal pragmatists such as Posner (1995). They put much more faith in judges’ insight into new situations than they do in formal rules and strained analogies with ancient precedents.