Law is a set of rules created and enforced by social or governmental institutions to regulate behavior, with its precise definition a matter of longstanding debate. It has been variously described as a science and as the art of justice. Law or the law may also refer to the profession of lawyers, judges and other people who work in legal systems.

Law may be a social construct, meaning that it is a human construction that we make up as we go along, rather than something that is built up by natural processes (like the laws of gravity). It can be seen as an arbitrary and subjective system that changes in response to human activity.

In order for a law to exist, there needs to be a participant who can assign true or false values to mathematically undecidable propositions (e.g., a judge presiding over a court case). The act of assigning these values is what forms the experience that a participant brings into the situation and the probability estimates she uses to predict whether or not a particular action will succeed. The participant’s prediction about the outcome of her action is a legal event, and as these events happen the law can be updated in response. This flowing process is what Holmes called “law”—a continually changing set of probabilities that are based on the participants’ own experiences and the interactions of those experiences with other people.

The aims of a functioning legal system vary from nation to nation, but generally include such objectives as keeping the peace, maintaining the status quo, preserving the rights of minorities against majorities, promoting social justice, and providing for orderly social change. Different legal systems have varied success in serving these purposes, ranging from those that are dictatorial in nature and oppress their populations to those that are democratically elected but lack stability or the ability to implement necessary social change.

There are several philosophies about what the law is and how it functions, known as schools of legal thought. The two main philosophies are natural law and legal positivism. Differentiating these philosophies is important to understanding the function and role of law. However, there is much more to the study of law than just understanding different philosophies. It is important to understand how law is connected to politics and how the laws of a country affect its citizens. This is why it is critical to understand political philosophy and the history of a nation’s political systems in order to fully appreciate the role of its law. It is also important to understand the difference between formal and persuasive sources of law, since these sources dictate how a judge should rule in cases. Examples of formal sources are statutes or legislation and judicial precedents, while persuasive sources can include foreign judgements, principles of morality, equity, or justice, and professional opinions. In addition, it is important to recognize that not all sources of law are legally binding.