Sources of Law
The unique characteristic of American law is that a very substantial part of it is not to be found in statutes enacted by legislatures but rather in cases decided by the courts. This concept of decided cases as a source of law comes to the USA from England. As a matter of fact, the US legal system is patterned after the English legal system rather than that of the rest of Europe or any other part of the world. The continental countries have codified their laws — reduced them to statutes — so that the main source of law in those countries is to be found in the statutes rather than in the cases.
In the USA statutes must be in keeping with the constitutions - federal and state - and the courts can overrule a statute that is found to violate constitutional provisions. Statutes and constitutions are classified as "written law". Also included under this heading are treaties that by the federal constitution are also a part of the law of the land. Case law, as opposed to written law, is not set forth formally but is derived from an analysis of each case that uncovers what legal propositions the case stands for.