Legal Definitions - key-number system

The key-number system is a sophisticated indexing and classification tool used in legal research, primarily developed by West Publishing Company (now Westlaw). Its purpose is to organize and categorize the vast body of American court decisions by assigning unique numbers to specific legal concepts or points of law. This system allows legal professionals to efficiently locate all published cases that discuss a particular legal issue, regardless of the jurisdiction or date of the decision, by simply looking up the corresponding key number. It functions much like a universal library catalog for legal principles found within court opinions.

Here are some examples illustrating the application of the key-number system:

• Imagine a defense attorney preparing for a trial involving a client accused of assault. The attorney wants to find all relevant case law concerning the legal defense of self-defense when the alleged victim was the initial aggressor. Instead of sifting through countless cases using broad keyword searches, the attorney can use the key number specifically assigned to "self-defense" under the "assault and battery" topic. This allows them to quickly identify and review all reported cases that have addressed this precise legal point, providing a comprehensive understanding of how courts have ruled on similar facts.

• Consider a law student writing a research paper on the concept of "duty of care" in premises liability cases, specifically focusing on the obligations property owners owe to invitees versus licensees. The student can utilize the key-number system to find the specific key number for "duty of care" within the broader "torts" (civil wrongs) category, then narrow it down to sub-categories related to "landowners" and "invitees/licensees." This ensures they gather all pertinent case law from various jurisdictions that have defined and applied these distinct duties, forming a robust foundation for their analysis.

• A judge's law clerk is drafting a court opinion in a contract dispute and needs to verify the established legal precedent regarding the elements required for a valid "offer and acceptance." To ensure the judge's reasoning aligns with existing law, the clerk can use the key number designated for "offer and acceptance" under the "contracts" topic. This provides an efficient way to access a curated collection of cases that have thoroughly discussed and applied these foundational principles of contract formation, helping the clerk to accurately cite and apply the law.