Secondary sources of law are written materials that explain, analyze, or comment on the law without being the law themselves. Treatises, legal encyclopedias, Restatements, law review articles, and legal dictionaries all fall into this category. Courts aren’t required to follow them, but judges and lawyers rely on them constantly to make sense of primary law and to find their way to the binding statutes and cases that control a given issue.1Legal Information Institute (LII) / Cornell Law School. Persuasive Authority
How They Differ From Primary Law
Primary law comes from government bodies with lawmaking power: the U.S. Constitution, federal and state statutes, administrative regulations, and judicial opinions. When a court within a given jurisdiction issues a decision, lower courts in that jurisdiction must follow its reasoning in later cases with similar facts.2Legal Information Institute (LII) / Cornell Law School. Supremacy Clause
Secondary sources are written by private individuals and organizations: law professors, practicing attorneys, judges writing outside their official role, and groups like the American Law Institute. Because they don’t come from a lawmaking body, no court is obligated to follow them. Their job is to organize and interpret the enormous mass of primary law so a researcher can actually use it. That makes them essential tools even though they sit below primary authority in the legal hierarchy.
How Much Weight Courts Give Them
Courts treat secondary sources as “persuasive authority.” A judge is free to adopt a secondary source’s reasoning, but is never required to. In practice, secondary sources carry the most weight in two situations: when no binding primary authority addresses the issue, and when the primary authority that does exist is ambiguous enough to support more than one reading.1Legal Information Institute (LII) / Cornell Law School. Persuasive Authority
Not every secondary source carries the same weight. Courts give more deference to sources written by recognized experts, sources with a long record of judicial citation, and sources that offer original analysis instead of surface-level summary. A leading treatise on federal civil procedure will outweigh a general encyclopedia entry on the same question. And if binding primary authority exists, citing a secondary source in place of it looks weak. Lawyers reach for secondary sources when they lack better options or want to add analytical depth to a primary-source argument.
The Main Types of Secondary Sources
Each major category serves a different research purpose. The right one to reach for depends on how much you already know about the issue.
Legal Encyclopedias
Legal encyclopedias summarize legal topics alphabetically, much like a general encyclopedia confined to the law. The two national sets are American Jurisprudence (Am. Jur. 2d) and Corpus Juris Secundum (C.J.S.), both covering virtually every subject area and pointing researchers toward relevant cases, statutes, and regulations.3U.S. Department of the Interior. Legal Encyclopedias Many states publish their own encyclopedias covering state law.
Use an encyclopedia at the start of a project when you need the basic framework, key terminology, and citations to follow. They are less useful for advanced work because they describe the law at a high level without the critical analysis courts find persuasive. Think of them as a map, not a guide.
Treatises
Treatises are comprehensive works on a specific area of law, written by recognized scholars or experienced practitioners. They can run to many volumes and cover a doctrine’s history, its current application across jurisdictions, and the tensions within it. Prosser and Keeton on torts, Corbin on contracts, and Wright and Miller’s Federal Practice and Procedure are standard examples.
The depth of a good treatise is what gives it weight in court. A treatise doesn’t just restate the law; it explains why the law developed as it did and sometimes argues for a particular interpretation. When a lawyer cites Wright and Miller on a procedural question, judges pay attention because the authors’ expertise is established.
Restatements of the Law
Restatements are published by the American Law Institute, an organization of prominent professors, judges, and lawyers. Each Restatement covers a broad area of common law and distills the prevailing rules from case law across U.S. jurisdictions into clear statements of principle. Restatements exist for contracts, torts, property, agency, conflict of laws, and several other subjects.4Legal Information Institute (LII) / Cornell Law School. Restatement of the Law
Each section opens with a “black letter” statement of the rule, then adds commentary and hypothetical illustrations. Courts cite Restatements often, and some states have formally adopted specific provisions as the governing law in their jurisdiction. That gives Restatements an unusual status: they start as secondary sources but can effectively become primary law once a court adopts them. Among secondary sources, they are among the most frequently cited and most likely to sway a decision.4Legal Information Institute (LII) / Cornell Law School. Restatement of the Law
Law Reviews and Bar Journals
Law reviews are academic journals published by law schools, typically edited by students, featuring long articles by professors, judges, and practitioners. A law review article might examine how courts have applied a doctrine across jurisdictions, critique a recent Supreme Court decision, or argue for a new interpretation to address an emerging problem. These articles often run thirty pages or more and carry extensive footnotes.
Bar journals are published by state and local bar associations and carry shorter, practice-oriented articles written mostly by working lawyers. A bar journal piece will focus on how a practitioner should actually handle an issue, not on academic theory. Both are secondary sources, but law review articles generally carry more weight with courts because of their depth.
American Law Reports (ALR)
ALR sits between encyclopedias and law review articles. Each entry, called an “annotation,” focuses on a single narrow legal issue and collects case law from across the country addressing it. An annotation might summarize the leading cases from every jurisdiction that has considered the enforceability of physician non-compete agreements, organize them by outcome, and cite related secondary sources.
ALR is especially valuable when you know the general area of law but need to see how different courts have handled a specific factual scenario. Someone has already done the work of gathering the cases. The trade-off is coverage: ALR doesn’t try to cover every topic, so whether a useful annotation exists on your issue is unpredictable.
Legal Dictionaries
Legal dictionaries define the specialized vocabulary of the law rather than analyzing it. Black’s Law Dictionary is the most widely cited. Courts occasionally cite dictionary definitions when the meaning of a statutory term is disputed, which gives these dictionaries a small but real role in judicial reasoning beyond helping researchers decode what they’re reading.
Practice-Oriented Secondary Sources
Some secondary sources exist less to explain the law in the abstract and more to help lawyers apply it day to day. These tend to be specialized, frequently updated, and tied to specific practice areas.
Loose-Leaf Services
Loose-leaf services compile primary and secondary materials on a specific area of law into a single, regularly updated resource. A loose-leaf service on labor law, for example, gathers the relevant federal and state statutes, implementing regulations, key agency decisions, and expert commentary in one place.
These services are most common in heavily regulated fields like tax, environmental law, employment, and securities. Their value is currency: they capture regulatory changes faster than treatises or encyclopedias, which may take months or years to publish new editions.
Jury Instructions and Form Books
Pattern jury instructions are standardized sets of instructions that courts give to juries on the legal standards they must apply. The judge’s chosen instructions in a case are primary law, but the published collections of pattern instructions are secondary sources. They break the elements of claims and defenses into plain language, which makes them a useful quick reference for understanding what a party has to prove.
Form books provide templates for contracts, pleadings, and motions. No one should file a template without adapting it to the specific situation, but these collections reflect established conventions and save drafting time.
Uniform Laws and Model Acts
The Uniform Law Commission drafts proposed legislation on subjects where consistency across states is desirable. A uniform act, like the Uniform Commercial Code, aims to establish identical rules in every state that adopts it.5Uniform Law Commission. FAQs A model act is less ambitious and expects state legislatures to modify it based on local conditions. In either case, the proposal has no legal force until a state enacts it. Before adoption, the draft is a secondary source. Once a state passes it, that state’s enacted version is primary law.6Legal Information Institute (LII) / Cornell Law School. Uniform Laws Courts also sometimes consult the official comments accompanying a uniform act to interpret ambiguous statutory language.
How to Use Secondary Sources in Research
The most effective technique is sometimes called the “one-hop” method. Start with a secondary source to orient yourself, then use its citations to jump straight to the relevant primary authority. A treatise or encyclopedia entry will cite the controlling statutes and leading cases on whatever issue it covers, which beats searching a case database cold.
Which secondary source you start with depends on what you already know. For a completely unfamiliar area, a legal encyclopedia gives you the big picture. If you understand the general framework but need depth on a specific issue, a treatise or ALR annotation is more efficient. For a genuinely novel question with no clear answer in existing law, a law review article may be the only source with anything useful to say.
Don’t stop at the secondary source. A clear treatise explanation can feel like the answer, but secondary sources can be outdated, can reflect the author’s preferred interpretation rather than the majority rule, and can miss recent developments. Use the secondary source to get pointed in the right direction, and then confirm what it says by reading the primary sources it cites.
Where to Access Secondary Sources
Many of the most valuable secondary sources sit behind expensive paywalls. Commercial databases like Westlaw and LexisNexis carry treatises, ALR annotations, legal encyclopedias, and law review articles, but individual subscriptions cost thousands of dollars per year. Law students get access through their schools, and practicing lawyers through firm subscriptions.
For everyone else, public law libraries are the best option. Most county and state law libraries provide free on-site access to commercial legal databases, including Westlaw and similar platforms. Remote access generally isn’t available, so you need to visit in person, but the access itself is free. Law school libraries sometimes allow public access to their physical collections, though policies vary. A growing number of law review articles are available through open-access repositories, and some older editions of well-known treatises have entered the public domain.