Law is the set of rules that people or governmental institutions create to regulate their interactions. Its precise definition is a longstanding source of controversy. Regardless of its exact nature, every society needs to have some form of law. It may take the shape of simple customs, a legal system, or even a single piece of legislation. But any form of law must be based on certain principles. These include adherence to human rights norms and standards, separation of powers, participation in decision making, accountability to the law, equality before it, and legal certainty.
Law also has to fit the reality of the physical world. It cannot mandate behaviours that are impossible to achieve or force people into situations that would be physically harmful.
The societal and economic context of law is a key determinant of its nature. Laws are most effective in societies and economies that allow citizens to have a voice in the process of government and have mechanisms for checking the power of their governments. Democracy is a crucial component of this, but it must be balanced with other forms of governing. For example, parliamentary systems can be highly effective at curbing excesses of the executive branch through procedures such as no confidence votes and regular elections.
Another factor is the level of social development that a nation-state (or country) has reached. A society that has advanced its knowledge of the physical world and its limitations can develop laws that are more effective at achieving their principal objectives than less developed societies. This can be seen in areas such as environmental law, where legislation is a powerful tool for change.
Lastly, the extent to which a society embraces scientific thought is an important factor in the creation and evolution of laws. Modern science, for example, has reshaped thinking about the shape and limits of law in ways that earlier writers such as Locke and Montesquieu could not have predicted.
Legal systems vary widely around the world. In common law jurisdictions, judicial decisions are acknowledged as “law” on equal footing with statutes adopted through the legislative process and regulations issued by the executive branch. The principle of stare decisis ensures that decisions by higher courts will bind lower ones to guarantee consistency in lawmaking.
The subject of law is vast and diverse, covering almost every aspect of life. However, three main categories can be identified: contract law, tort law and property law. Contract law covers agreements that involve a transfer of goods or services, such as buying a bus ticket or trading options on the stock market; tort law deals with harms caused to individuals, whether by an automobile accident or defamation; and property law covers ownership of tangible assets such as land and buildings or intangible assets such as stocks and shares. The principles of these subjects converge with each other in many instances.