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Circuit Riders: Basic Legal Research

A guide for non-law librarians

The U.S. Legal System


This unit on the U.S. Legal System includes sections on Sources of Law and Weight of Authority and Civics Education Resources for all ages.

It ends with a review video that describes our federal and state (South Carolina) systems of government using examples of how the legislative, executive, and judicial branches work together.

Sources of Law

To understand the legal research process, begin with how our legal system works. The United States legal system has three systems of government; federal and state, each of which has its own set of laws, and a third system of government, that of the Native American nations. Tribal Nations also have their own set of laws. (This guide does not delve into this area of law, but there are resources available. See, our guide on American Indian and Indigenous Law.)

The four sources of federal and state law are:

  1. constitutions;
  2. statutes and ordinances;
  3. rules and regulations; and
  4. case law.

Constitutions are the foundation of our legal system. All federal and state governmental authority flows from the United States Constitution and the state constitutions.
The United States Constitution is the "supreme law of the land" and no laws, state or federal, may violate it. Each state has its own constitution. The laws of a particular state may not conflict with the constitution of that state or the U.S. Constitution.

Federal and State Laws

The Separation of Powers doctrine divides governmental authority among three branches: Legislative, Executive, and Judicial. These three branches of federal and state government are responsible for creating the remaining sources of law

  • Legislative branches enact laws called statutes and ordinances.
  • Executive branches enforce and implement these laws through rules and regulations.
  • Judicial branches interpret these laws by deciding cases and issuing written opinions.

Flowcharts of the federal and state legal systems as described above.


Weight of Authority

Scales of justice.


Identifying the rules that apply to a particular legal issue in your jurisdiction requires legal research. The legal research process involves not only locating legal authorities, but also determining their importance. 


Primary v. Secondary
Legal researchers utilize two types of authority, referred to as primary and secondary authority.

Primary authority is the law, which includes constitutions, statutes and ordinances, rules and regulations, and case law. These authorities form the rules that courts follow.

Secondary authority is not the law. Secondary authorities, such as legal dictionaries and encyclopedias, books and treatises, and journal articles, explain and analyze the law and help researchers both understand and locate primary authorities.


Mandatory v. Persuasive
Authorities that courts must follow are called mandatory (or binding) authority.
Authorities that courts may follow if persuaded to do so are called persuasive (or non-binding) authority.

Secondary authority is always persuasive.

Primary authority (the law) may be mandatory or persuasive depending upon:

  • the jurisdiction where the dispute is to be decided; and
  • the level of the court that decided a particular case.

U.S. Legal System Video

This video describes our federal and state (South Carolina) systems of government using examples of how the legislative, executive, and judicial branches of each system work together.