Measuring Legal Concepts

Abstract

Concepts are said to be the building blocks of law, underlying the rules, standards and principles that comprise legal doctrine. Despite the acknowledged importance of legal concepts, it remains an open question which of all legal concepts are most fundamental to law.

This Article attempts to identify the core and penumbra of the legal concept space by developing a novel conceptual and methodological framework for measuring how fundamental a given concept is to law. The paper then implements that framework through one a series of three empirical studies featuring an analysis of: (a) every entry in Black’s Law Dictionary; (b) all federal statutes and regulations currently in force; (c) ~1 million judicial decisions; and (d) ~600,000 private contracts.

Analyses reveal that less than 2% of all legal concepts underlie the majority of the legal concept space and comprise the majority of references to legal concepts within legal doctrine. Comparing across sources of law reveals a strong correlation between how often a concept is invoked within codified legal instruments (“law in books”) and how often it is invoked within judicial decisions (“law in action”), as well as between a concept’s centrality within public legal instruments and its centrality within private legal instruments. Comparative analyses between legal sources as a whole and non-legal corpora—including the entirety of the Google Books corpus (n=300 billion words)—further reveal that the most fundamental legal concepts are disproportionately more likely than peripheral legal concepts to appear in ordinary written and spoken communication.

Taken together, these results suggest that legal doctrine is largely built upon a small core of foundational legal concepts, such as reasonable, personhood, and consent, which traverse multiple areas of law and more closely resemble ordinary concepts accessible to laypeople than specialized concepts requiring expert legal knowledge. Surrounded by this core is a massive penumbra of technical legal concepts, such as tortious interference, parol evidence, and fee simple determinable subject to executory interest, seldom encountered by jurists and laypeople alike. By illuminating the legal concept space, this Article provides a clearer view of the nature of legal doctrine that provides novel evidence for classic jurisprudential debates along with decision-relevant insights for legal practice and education.

Keywords: empirical legal studies, legal education, experimental jurisprudence, law and psychology, law and cognitive science, natural language processing

JEL Classification: K10,K12,K30,K40,K49