An authoritative source, in the legal context, is a body of law which takes precedence over others. An authoritative source is known to be reliable because its authority or authenticity is widely recognized.
All legal information comes from either primary or secondary sources. Primary sources articulate the law. Primary sources include the following: Constitutions, treaties and other binding international agreements, statutes as enacted, statutes as codified, agency regulations, court decisions, decisions by agency adjudicative bodies, executive orders, presidential proclamations, and certain government orders (such as some military orders, including some verbal ones).
Court decisions, often referred to as case law, have their own hierarchy of most authoritative to least authoritative. Within the federal system, case law from the United States Supreme Court is the most authoritative source of law on an issue. Next would be case law from the federal circuit court of appeals, then decisions by federal district courts. In the state context, the decision of the Supreme Court of a particular state is the most authoritative source of law on a state law issue, followed by state appellate courts, and state district/circuit courts.
While primary sources articulate the law, secondary sources analyze the law. When writing a memo or a brief, you must rely on relevant primary sources. However, secondary sources are referred if no primary sources exists or adding support to the secondary authority.
A secondary authoritative source is one that has been written by an expert who is recognized in his or her field of expertise; some examples include peer-viewed journal articles, government websites, public records and books by reputable, well-known publishers. Some sources to look for are those that contain complete first-hand accounts of an event that happened and lack a one-sided view.
Secondary sources are a helpful place to start research, especially if the assigned topic is unfamiliar. Writers can save time since secondary sources provide an overview of the legal issues and point to relevant primary authority.
There are several reliable secondary sources: Hornbooks, Legal Encyclopedias, American Law Reports (ALR), Periodicals are reliable secondary sources.
Legal sources such as books about laws and articles about laws in magazines and academic journals may be reliable sources. Whether a legal source is reliable or not needs to be considered separately for each source. Law sources that are written by authoritative experts in law, such as legal scholars, and published by respected independent publishing houses are generally reliable sources.