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Northern Illinois University
College of Law
David C. Shapiro Memorial Law Library

Basic Legal Research

Understanding Courts and Legal Authority

Understanding the basic structure of the U.S. court systems and the hierarchy of their authority is a vital skill for any legal researcher. Without this skill you will be unable to determine whether a given authority is mandatory or persuasive.

  • The United States is a common law system. This means courts decide disputes. These decisions develop into legal principles that will apply to future similar cases.
  • The prior decided cases create precedent.  Precedent is mandatory authority within the jurisdiction where the precedent was issued.
  • Other jurisdictions may look at these decisions persuasively, but are not bound to the decisions outside their jurisdiction.

Legal Terminology Related to Courts & Legal Authority

Authority: Items that may bind a court or influence a court. Jurisdiction and court level determine whether legal authority is mandatory or persuasive.

  • Mandatory (Binding): Authority that a court must follow, i.e., that is binding on a court.
  • Persuasive: Authority that a court may, but is not bound to, follow. For example, decisions from one jurisdiction may be persuasive authority in the courts of another jurisdiction.

Precedent: A judicial decision that creates a rule that other courts must follow when deciding later cases that are similar or identical to the case that created the rule.

Court Opinion: The written decision issued by the court.

Jurisdiction: A court's power to hear matters and issue binding decisions.

Trial Court: Trial courts are at the bottom of the judicial hierarchy in a jurisdiction.  They are usually persuasive primary authority.  Trial court opinions bind the parties involved in the case, but other trial courts hearing similar cases are not bound by the opinions, and the appellate courts in the jurisdiction are not bound by the trial court opinions.

Intermediate Appellate Court: The middle of the judicial hierarchy in a jurisdiction, they are considered the intermediate court.  Their opinions are binding on the courts below them (trial courts). 

Supreme Court: The court of last resort, or the highest court in the judicial hierarchy.  The opinions of a supreme court are binding on all the courts below it (Trial and Appellate).


Amy E. Sloane, Researching the Law 15 (2014).

Federal Courts Structure & Maps

Illinois Courts Structure & Maps

Illinois Court Structure

Illinois Circuit Court map


Amy E. Sloane, Researching the Law 15 (2014).


Videos About Court Authority

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