Sources of American Law
American law comes from a variety of sources: the Constitution, state constitutions, federal and state statutes, and case law. Understanding this is important because litigants must identify the source of law in their complaint to bring suit in federal court.
Federal and State Constitutions
The Constitution of the United States is the supreme law of the land — no law, regardless of its source, can contravene it. In essence, the Constitution establishes a guideline by which all federal and state laws and regulations must adhere; any law found in violation of the Constitution is declared unconstitutional by the Supreme Court. Over the course of 200 years, the Supreme Court has compiled a vast body of constitutional law based on its interpretation of various phrases and clauses found in the Constitution. These interpretations, of course, have sometimes varied from court to court, which is how the law evolves over time.
Likewise, state constitutions are the supreme law within their respective borders, unless they contradict the U.S. Constitution, an act of Congress, or the provisions of a foreign treaty. Just as the Supreme Court interprets the Constitution, so does the highest court in each of the states interpret its own state's constitution.
Legislative acts constitute a rapidly growing area of American law. Every year, tens of thousands of legislative bodies promulgate new laws and regulations that govern our lives, covering everything from zoning rules to highway speeds, the disposal of hazardous waste, and criminal conduct. Congress and the state legislatures are the best known of these bodies, but county, municipal, and district governments also contribute to statutory law. It has been estimated that there are nearly 50,000 governmental bodies in the United States that act in a legislative capacity.
Stare decisis, Latin for “let the decision stand,” is a doctrine by which the lower courts (as well as the Supreme Court itself) follow precedents established in earlier rulings when deciding a case. While the courts are not absolutely bound by stare decisis, it's highly unusual for them to disregard established case law. Perhaps the biggest violator of stare decisis is the Supreme Court itself.
Through the years, decisions rendered by the various courts have formed a body of law referred to as “case law.” Unlike statutory law or administrative regulations, which are codified and highly organized, case law is found in court opinions, and is generally tied to the particular facts of a case. Sometimes case law is referred to as “unwritten law,” although this is a misnomer.
Case law is a product of our common-law tradition, which was inherited from Great Britain. “Common law” is another way of saying judge-made law. Its origins date back to the Norman conquest of England, when William the Conqueror established a unified legal system based on the rulings of the king's court. The more important decisions from the king's court were collected in something called the Year Books, which served as the basis for settling similar disputes.
Case law differs from statutory law in that it is flexible, and can evolve over time to reflect society's changed values. To some extent, it is the ability of case law to adapt to the times that has helped make the Constitution a “living document,” as many scholars refer to it. Today, a dozen countries have common-law systems, including former British colonies Canada, Australia, India, and New Zealand.