Law is the system of rules that a society or government develops to deal with criminal and business activities and with social relationships. It is a very complex subject and it can be applied in many different ways. It is an important idea that has been debated for millennia and it is impossible to understand modern societies without understanding the role of the law. It is an essential concept for a democracy and it has been defended by philosophers and politicians from Aristotle (c. 350 BC) through the medieval philosophers Sir John Fortescue and Niccolo Machiavelli; by the Enlightenment writers such as Montesquieu (1748); and by American constitutionalism in The Federalist Papers.

There are many different definitions of the law but it is generally understood to be a set of enforceable standards that guides behaviour. It is usually a matter of public knowledge and it should be transparent and objective. It is often based on social and economic interests, but it also has religious and moral dimensions. It is generally agreed that it should not compel people to do things which are immoral or beyond their abilities. It is a general principle that the law must be well-drafted and clear and that it should be enforced consistently and fairly.

It is also usually agreed that the law should be open and accessible to all members of society. The requirement for access is one of the central tenets of the Rule of Law and it requires that laws be publicly available, easily digestible by individuals and that they should be published in advance of their being applied so that individuals can be held responsible for obeying them. It is usually also required that law be formulated and implemented by expert authorities in an objective way, and it should be codified into a coherent form so that laws on similar subjects fall together and are not spread out in a confusing manner.

In practical terms this means that laws must be written, drafted by professionals in the field and put into a form that can be printed and distributed. They must then be read and understood by individuals, and they must be interpreted in a context of changing social circumstances. The requirements for clarity and certainty can be challenging to meet in practice, but they are a necessary part of the philosophy of the law.

Some legal systems are more effective than others at serving these various purposes. For example, an authoritarian regime may keep the peace and maintain the status quo but it is likely to oppress minorities or political opponents. In contrast, a democracy based on the rule of law is more likely to allow for change and to promote social justice. There are, however, many other factors that influence how well a particular legal system serves its purpose. These include the ability of a government to keep the peace, to prevent civil war and foreign invasions and the capacity of judges to interpret and apply the law in a fair and consistent manner.