Case Law Research

Understanding Case Law and Precedent

Case law—the body of law derived from judicial decisions—forms the backbone of the American legal system. Unlike statutes, which are enacted by legislatures, case law develops through the accumulation of court decisions over time. Understanding how precedent works is essential to effective legal research.

What Is Precedent?

Precedent (also called stare decisis, Latin for "to stand by things decided") is the principle that courts should follow the rules established in prior decisions when deciding similar cases. This doctrine serves several purposes:

• Predictability — Parties can anticipate how courts will rule based on prior decisions
• Consistency — Similar cases receive similar treatment
• Efficiency — Courts don't need to reason through every issue from scratch
• Legitimacy — The legal system appears fair when like cases are treated alike

Binding vs. Persuasive Authority

Not all precedent carries the same weight. The key distinction is between binding (mandatory) and persuasive authority:

• Binding authority — A court must follow these decisions. Generally, a court is bound by decisions from higher courts within the same jurisdiction.
• Persuasive authority — A court may consider these decisions but is not required to follow them. This includes decisions from courts in other jurisdictions, lower courts, or courts at the same level.

Court Hierarchy and Binding Authority

Understanding which courts' decisions bind which other courts is fundamental to case law research. The analysis differs for federal and state court systems.

Federal Court System

The federal court system has three levels:

1. U.S. Supreme Court — Decisions bind all federal and state courts on questions of federal law
2. U.S. Courts of Appeals — 13 circuits; decisions bind district courts within that circuit
3. U.S. District Courts — Trial courts; decisions do not bind other courts but may be persuasive

Circuit Court Binding Rules

• A circuit court's decisions bind all district courts within that circuit
• A circuit court's decisions do not bind other circuit courts (though they may be persuasive)
• A circuit court panel is generally bound by prior panel decisions within that circuit
• Only an en banc decision (the full circuit) or Supreme Court decision can overrule circuit precedent

State Court Systems

Most states have a three-tier system similar to the federal structure:

1. State Supreme Court (sometimes called Court of Appeals or Supreme Judicial Court) — Final authority on state law
2. Intermediate Appellate Courts — Bind trial courts within their geographic or subject matter jurisdiction
3. Trial Courts — Decisions generally do not bind other courts

State Law in Federal Court

When federal courts decide state law issues (typically in diversity jurisdiction cases), they must apply state law as the state's highest court would. Federal courts will:

• Follow the state supreme court's decisions on state law questions
• Consider intermediate appellate court decisions as strong indicators of state law
• Attempt to predict how the state supreme court would rule if no controlling decision exists

Finding Cases

There are several methods for finding relevant cases. Experienced researchers typically combine multiple approaches for comprehensive results.

The Digest System and Key Numbers (Westlaw)

West's Key Number System is one of the most powerful tools for case research. Understanding how it works will dramatically improve your research efficiency.

How the Key Number System Works

West editors read every published case and identify the legal propositions discussed. Each proposition is:

1. Summarized in a headnote (a brief statement of the legal point)
2. Assigned to a Topic (one of approximately 450 broad legal subjects)
3. Given a Key Number within that topic (a specific subdivision)

For example, the topic "Negligence" contains hundreds of Key Numbers, each addressing a specific aspect of negligence law—such as "Negligence k272" for "Duty of care toward invitees."

Using Key Numbers to Find Cases

Understanding and Using Headnotes

Headnotes are editorial summaries that appear at the beginning of cases in Westlaw, Lexis, and other databases. They are powerful research tools but come with important caveats.

What Headnotes Contain

• Summary — A brief statement of a legal point from the case
• Classification — Topic and Key Number (Westlaw) or Headnote Topic (Lexis)
• Location pointer — A link to where in the opinion this point is discussed

How to Use Headnotes Effectively

• Scan for relevance — Quickly review headnotes to determine if a case addresses your issue
• Navigate to relevant sections — Click the headnote to jump directly to that portion of the opinion
• Find related cases — Click the classification to find other cases on the same point
• Extract search terms — Headnotes use legal terminology that can improve your searches

Natural Language vs. Boolean Searching

Modern legal databases offer two primary search methods. Understanding both—and when to use each—makes you a more effective researcher.

Natural Language Searching

Natural language searching allows you to type a question or description in plain English. The database uses algorithms to interpret your query and return relevant results.

When to use natural language:

• You're unfamiliar with the legal terminology for your issue
• You want to cast a wide net at the beginning of research
• You're exploring a new area of law
• Your issue doesn't have standard legal phrasing

Example: "Can an employer fire an employee for refusing to violate a law?"

Boolean (Terms & Connectors) Searching

Boolean searching uses specific operators to define precise relationships between search terms. This gives you more control over results.

Key Boolean operators:

• AND — Both terms must appear (often the default): negligence AND premises
• OR — Either term may appear: employee OR worker
• /n — Terms within n words of each other: wrongful /3 termination
• /s — Terms in the same sentence: summary /s judgment
• /p — Terms in the same paragraph: duty /p care /p invitee
• "" — Exact phrase: "reasonable person"
• ! — Root expander (truncation): negligen! finds negligence, negligent, negligently
• * — Wildcard for variable characters: wom*n finds woman, women
• % or NOT — Exclude a term: discharge % firearm

When to use Boolean:

• You know the precise legal terminology
• Natural language returns too many irrelevant results
• You need specific phrases to appear near each other
• You want to exclude certain contexts (like "discharge" in employment vs. firearms)

The "One Good Case" Method

One of the most efficient research strategies is finding a single highly relevant case and using it as a springboard to find others. This method leverages the interconnected nature of legal authority.

Starting Points for Finding That First Case

• Secondary sources — Treatises and practice guides cite leading cases
• Class materials — Cases from your courses may be relevant
• Supervising attorney — Ask if they know of any starting points
• General searching — A natural language search may surface a good case
• Legal-specific AI tools — If permitted, tools like Deep Research AI or Lexis+ AI may suggest a starting case (but you must still verify it and trace how you could have found it conventionally)

Expanding from One Good Case

Once you have a relevant case, use these techniques to find more:

1. Review headnotes — Identify relevant Key Numbers and explore those classifications
2. Check "Citing References" — Use KeyCite or Shepard's to find cases that later cited your case
3. Review "Cases Cited" — Look at the authorities your case relied upon
4. Use "Related Cases" — Both Westlaw and Lexis offer algorithmically related cases
5. Extract terminology — Note how the court phrases the legal standard and use those terms in new searches

Reading and Analyzing Cases

Finding cases is only half the battle. Understanding how to read and analyze them is equally important. This section explains the structure of judicial opinions and how to extract what you need.

Parts of a Case

A typical appellate opinion contains these components:

Caption and Procedural Information

• Case name — The parties involved (e.g., Smith v. Jones)
• Citation — Where the case can be found
• Court and date — Which court decided and when
• Procedural posture — How the case reached this court (appeal from summary judgment, etc.)

The Opinion

• Facts — What happened to bring the parties to court
• Issue(s) — The legal question(s) the court must decide
• Rule — The legal principle(s) the court applies
• Application/Analysis — How the court applies the rule to the facts
• Holding — The court's decision on the legal issue
• Disposition — What the court orders (affirmed, reversed, remanded)

Holding vs. Dicta

One of the most critical distinctions in case analysis is between holding and dicta:

• Holding — The court's decision on a legal issue that was necessary to resolve the case. Holdings are precedential and may be binding on future courts.
• Dicta (or obiter dictum) — Statements in the opinion that are not essential to the decision. This includes hypotheticals, commentary on issues not before the court, and observations that go beyond what's necessary to decide the case. Dicta is not binding precedent, though it may be persuasive.

Identifying Key Facts and Legal Issues

Not all facts in a case are equally important. Learning to distinguish key facts from background information is essential:

Key Facts

Key facts (or "legally significant facts") are those that, if changed, would likely change the outcome. Ask yourself: "If this fact were different, would the court have reached the same result?"

Legal Issues

The legal issue is the question of law the court must answer. It typically combines a legal standard with the key facts. For example:

• "Whether a landlord who knew of a tenant's dangerous dog owed a duty of care to visitors."
• "Whether an employee's refusal to commit perjury constitutes protected activity under the wrongful discharge doctrine."

Reading Strategy

1. Read the headnotes — Get an overview of what the case covers (but remember, don't cite them)
2. Identify the procedural posture — Know what ruling is being appealed
3. Find the issue — Courts often state the issue explicitly
4. Extract the rule — Identify the legal standard the court applies
5. Understand the reasoning — See how the court applies the rule to reach its conclusion
6. Note the holding — Understand exactly what the court decided

Expanding from One Case to Related Cases

Once you've found and analyzed a relevant case, use these strategies to systematically expand your research.

Using Citators to Expand Research

Citators (KeyCite on Westlaw, Shepard's on Lexis) serve two functions: verification and expansion. For expansion:

• Citing References — Find every case, statute, and secondary source that cites your case
• Table of Authorities — See what authorities your case cited, which may lead to seminal cases
• Negative Treatment — Cases that distinguish or criticize your case may present the opposing view or alternative approaches

Following Headnote Classifications

Each headnote in your case has been classified. Click through to find all other cases with the same classification. This is particularly effective because:

• Human editors have determined these cases address the same legal point
• You can limit by jurisdiction to find binding authority
• You may discover cases your keyword searches missed

Using "More Like This" Features

Both Westlaw and Lexis offer features that algorithmically find similar cases:

• Westlaw: "Related Cases" and "More Like This Headnote"
• Lexis: "More Like This" and "Search Within Results"

These can surface relevant cases that don't share exact terminology with your starting case.

Checking Secondary Sources

Don't forget to return to secondary sources after finding cases. A treatise or ALR annotation might cite additional relevant authorities you haven't discovered through case-based research.

Westlaw vs. Lexis for Case Research

Both Westlaw and LexisNexis are comprehensive legal research platforms. For case law research, each has distinct strengths.

Westlaw Advantages

• Key Number System — West's proprietary classification system is unique to Westlaw and is the most comprehensive subject organization of case law
• Headnote consistency — West has used the same classification system since the 1800s, making it easier to track how courts have treated issues over time
• KeyCite — Some researchers prefer KeyCite's interface and depth indicators
• Digest searching — Direct access to the West Digest System

Lexis Advantages

• Search Within Results — Lexis's ability to search within search results is particularly flexible
• Shepard's Reports — Some prefer Shepard's detailed treatment analysis
• Practice Area Pages — Well-organized by substantive area
• Natural language search — Some researchers find Lexis's natural language algorithms more intuitive

Practical Recommendations

• Use Westlaw when you want to leverage Key Numbers and digest classification
• Use Lexis when you prefer its search interface or Shepard's treatment analysis
• Use both for comprehensive research—different editorial decisions mean each may surface cases the other doesn't
• Check the same case in both to see different headnote classifications that might lead to different related cases

Unpublished Opinions and Their Treatment

Not all judicial opinions are "published" in the traditional sense. Understanding the distinction between published and unpublished opinions is important for research and citation.

What Are Unpublished Opinions?

Courts designate some opinions as "unpublished" (also called "non-precedential" or "not for publication"). These decisions:

• Do not appear in official print reporters (like F.3d or regional reporters)
• Are typically available in electronic databases and may appear in "appendix" reporters (like the Federal Appendix)
• Often involve straightforward applications of settled law
• May be shorter and contain less detailed analysis

Citation Rules for Unpublished Opinions

Rules about citing unpublished opinions vary significantly by jurisdiction:

Federal Courts

Federal Rule of Appellate Procedure 32.1 allows citation of federal unpublished opinions issued after January 1, 2007. However:

• Courts may accord them less weight than published opinions
• They are generally not considered binding precedent
• Local circuit rules may impose additional requirements

State Courts

Rules vary dramatically by state. Some states:

• Prohibit citation of unpublished opinions entirely
• Allow citation only for limited purposes (like law of the case)
• Allow citation but require disclosure that the opinion is unpublished
• Treat them the same as published opinions

Finding Unpublished Opinions

On Westlaw and Lexis, unpublished opinions appear in search results alongside published opinions. To identify them:

• Westlaw: Look for "Not Reported" or the Federal Appendix citation (Fed. Appx.); filter using "Status" options
• Lexis: Check the "Publication Status" field; use filters to include or exclude unreported decisions

When Unpublished Opinions Are Useful

Even where citation is restricted, unpublished opinions can be valuable for:

• Understanding how a court applies law — See how judges handle similar facts
• Finding cited authorities — The cases an unpublished opinion cites may be useful published authorities
• Predicting outcomes — Patterns in unpublished decisions may suggest how a court will rule
• Identifying arguments — See what arguments parties have made in similar cases

Next Steps

Now that you understand case law research, continue building your skills:

• Citators — Learn to use KeyCite and Shepard's to verify your cases and expand your research
• Statutory Research — Understand how to research statutes, which cases often interpret
• Secondary Sources — Review how secondary sources can lead you to relevant case law