Law is a field of study that encompasses all of the rules and guidelines of an activity or agreement that are recognized as binding on participants. It serves four principal purposes: setting standards, maintaining order, resolving disputes, and protecting liberties and rights. It is the source of a broad range of scholarly inquiry in history, philosophy, social science (such as sociology and economic analysis), and empirical science (such as meteorology). Law also describes all professions that deal with advising people about laws or representing them in court.
Laws are created by governments at every level: federal, state, and local. Federal laws govern the entire nation, whereas state and local laws apply to the citizens of that state or municipality.
Most of the world uses a civil law system, in which the sources that are recognized as authoritative are primarily legislation-that is, statutes and constitutions passed by government-and custom. The modern world’s civil law systems largely derive from a 6th century AD codification of the legal practice of the Roman Empire by the Byzantine Emperor Justinian, known as the Corpus Juris Civilis.
Religious law is based on precepts from the teachings of religious scripture. Examples include Jewish Halakha, Islamic Sharia, and Christian canon law. These sources can be interpreted and supplemented by human elaboration through the methods of ijtihad (reasoning by analogy), Qiyas, and Ijma. These methods differ from those of natural (empirical) science, which are descriptive rather than normative.