There are three bases of American law:
The American legal system has its roots in the British system, which is based on common law. In this system, judges shape the law through their decisions, interpretations, and rulings, which are then collected into a body of law known as case law that other judges can use as reference. When judges make decisions, they look to similar cases for precedent, a court ruling from the past similar to the current case. The Latin phrase stare decisis denotes the legal doctrine of relying on precedent.
Example: The Fourth Amendment states that citizens are protected from “unreasonable searches and seizures” and that search warrants can only be issued based on “probable cause.” Many cases have laid down rules about how the courts should handle such matters. In the case Mapp v. Ohio (1961), the Supreme Court applied the exclusionary rule—which states that any evidence obtained through an illegal search is excluded from trial—to state courts. Since then, judges have referred to the precedent set in Mapp v. Ohio to keep illegally obtained evidence out of the courtroom.
The U.S. Constitution is the supreme law of the land. No law or act of government—at the local, state, or federal level—can violate its principles. Similarly, a state’s constitution is the supreme law within the state’s borders, so long as the state constitution does not conflict with the national Constitution.
Federal courts have assumed the power of judicial review, the right to determine the constitutional legality of state and federal laws, congressional and presidential acts, and lower-court rulings. Likewise, each state court has assumed the power to determine the legality of legislative and gubernatorial decisions within its own borders.
The power of judicial review is not codified in the Constitution, however. Many state supreme courts had already assumed this power by the time the Constitution was ratified in 1789, and Chief Justice John Marshall set a precedent for federal judicial review in the 1803 case Marbury v. Madison. Federal courts use their power of judicial review sparingly, primarily because they have no means of enforcing their decisions. Nevertheless, judicial review is the most significant power of the judiciary branch.
Statutes are laws passed by Congress and states legislatures. Congress passed an unprecedented number of statutes in the twentieth century, covering such issues as environmental regulation, criminal law, and contracts. State governments can also pass statues according to the rules of their own constitutions. Some government agencies can issue administrative regulations, which have the force of law.
There are two types of courts in the United States: federal and state. Each type of court has a certain jurisdiction, the unique power to hear and decide on certain types of cases. Federal courts, for example, have jurisdiction over cases that involve the national government or parties from more than one state or from another country. Only federal courts can hear these cases, not state courts. Each state court has jurisdiction over cases that involve disputing parties from within its own borders. There are four types of jurisdiction:
These types of jurisdiction are not mutually exclusive, which means that a court might have both original and limited jurisdiction or appellate and general jurisdiction.