Earlier court decisions guide how later, similar cases should be decided

Precedents create consistent legal rules over time

Courts generally follow prior decisions to ensure stability and predictability

Promotes equal treatment for similar cases

A court resolves a dispute and articulates a legal principle

Later courts adopt and apply that principle in comparable situations

Repeated application turns principles into well-established legal rules

Rules are refined as new fact patterns arise

Courts clarify definitions, standards, and exceptions over many decisions

Judges compare current facts to earlier cases

They extract governing legal principles and apply them to the dispute

Even when statutes exist, courts interpret ambiguous terms

Judicial interpretations can effectively shape how statutes operate in practice

Decisions of higher courts bind lower courts within the same jurisdiction

Trial courts must follow appellate and supreme court rulings

Binding precedent

Persuasive precedent

Vertical precedent

Horizontal precedent

The legal rule necessary to decide the case

The portion that typically carries precedential force

Comments not essential to the outcome

May be persuasive but usually not binding

Small factual differences can limit a precedent’s reach

Courts define which facts are “material” to the rule

A court follows precedent in principle but finds the current case materially different

Limits precedent without overruling it

A higher court (or sometimes the same high court) replaces an earlier rule

Usually justified by

Common law often changes gradually through a series of decisions

New exceptions and clarifications accumulate

Legislatures enact statutes; courts apply and interpret them

Common law fills gaps where statutes are silent

A clear statute can replace or modify common-law rules

Courts then interpret the statute and apply it to cases

Some areas of common law are later written into statutes

Courts still interpret coded rules, creating new precedent about their meaning

Negligence standards, duty of care, causation principles

Offer/acceptance, consideration, remedies, implied terms

Easements, possession doctrines, nuisance

Some jurisdictions historically recognized common-law crimes; many are now statutory

Similar cases tend to have similar outcomes

Lawyers can advise clients by referencing prior cases

Courts can adjust rules to new contexts without waiting for legislation

Written judgments become primary legal sources

Legal research often focuses on finding and analyzing relevant precedents

Large numbers of cases can make the law difficult to navigate

Different courts may interpret precedents differently until clarified by higher courts

Judges are not legislators; judge-made law can raise separation-of-powers debates

Extensive litigation and legal research can be expensive

Primary source: judicial decisions and precedent (alongside statutes)

Method: reasoning from cases to rules

Primary source: comprehensive codes and statutes

Method: applying codified rules, with less reliance on binding precedent (though case guidance may still matter)

Courts decide what counts as “foreseeable” and “reasonable”

Over time, detailed standards develop through repeated decisions