Law is the system of rules and principles that a society recognizes as binding upon its members. It includes both the body of laws that a government enacts and the customs and policies that are recognized as legal by judicial decisions. It can also be defined as the set of commandments and principles that a people accept as divinely mandated or morally sanctioned. The study of the law is referred to as jurisprudence.
The most fundamental aspects of a nation-state’s system of law include its political structure, the nature of power that supports it and the extent to which the state’s citizens enjoy basic civil liberties. These factors differ from nation to nation. Despite these differences, certain features are common to all nation-states. For example, the fact that law is a product of political action means that the existence of law depends on who has the power to make and enforce it. The people or groups that have the military strength to dominate a region tend to have control over politics and law, though revolts against existing political-legal authority are a recurrent feature of most nations.
In the United States, the law is primarily administered by the federal government. Federal law traditionally focused on areas where there was an express grant of legislative power to the federal government, like the military, money, foreign relations (especially international treaties) and tariffs, but broad interpretations of various clauses in the Constitution have enabled the scope of federal law to be expanded.
State and local government have jurisdiction over a number of matters in the United States, including some areas that fall within the sphere of national law. State and local governments also have the power to regulate a number of aspects of daily life, from land use planning to traffic enforcement. State and local governments can also pass laws relating to specific industries, such as tobacco or firearms.
An important element of a system of law is that it must be interpreted and enforced by a judge or other legal official. Judges can decide cases based on the written words of the constitution, a statute or a court decision. Court cases are usually preceded by a written complaint, which details the facts of the case and why the plaintiff is seeking a remedy. The plaintiff may be represented by a lawyer, and the defendant will usually have a lawyer as well.
When a court decides a case, it typically issues a written opinion that explains its reasoning and makes a final decision. The opinion identifies the applicable law and refers to earlier cases that have provided a precedent that the judges must follow in reaching their decision. The opinion also identifies the governing legislation or textbook that the judges used to support their decision. The judge’s opinion is usually cited by future courts in the same case or in similar cases. When a judge’s decision is appealed, an en banc panel of judges will generally hear the case.