While there are a variety of types of laws that govern, there is a hierarchy to the U.S. legal system.
The legal pyramid is as follows:
III. Administrative Regulations (carry the same weight as statutes)
IV. Case law (court opinions)
When we refer to 'authority' or 'primary authority', we mean "the law." The law being a constitutional or statutory provision, an administrative regulation or a court opinion. 'Secondary authority' refers to material that is NOT the law, but that which leads you to the law or helps to explain the law. Secondary authority is located in legal encyclopedias, jurisprudences, and Amerian Law Reports (ALR), among others. Refer to the tab on secondary sources for more information.
'Authority' or 'primary authority' is divided into two types, mandatory and persuasive. For authority to be mandatory, the court in your jurisdiction (determine jurisdiction at the outset even if the matter is not being litigated) MUST follow the legal rule(s) set forth in the authority you are relying on for your legal situation. Persuasive authority is everything else. Secondary authority is always persuasive. Do not rely on secondary authority unless there is absolutely no primary authority that supports your position.
There are three levels of court: trial, appellate, and court of last resort. Trial is self-explanatory-- it's the basic level, where the action is first brought. Appellate is the next level up, where the losing party at trial can appeal for a different result based on error in the trial court's judgment. Court of last resort (often called the Supreme Court) is the jurisdiction's highest court. The losing party in an appellate case can appeal to this court, again basing the appeal on error in the appellate court's decision.
In the Federal system, the chain goes District Court, Circuit Court of Appeals, and Supreme Court of the United States. State courts may have other names for their court levels. For example, Florida's court system is slightly opposite the Federal-- Circuit (or County) Court, District Court of Appeals, and Supreme Court of the State of Florida.