Definition
To cross, cut across, or meet at a point. In legal usage, the term carries two distinct applications:
1. Physical intersection: The crossing of one physical thing by another — roads, railways, property lines, waterways. This is the dominant legal sense in older property, highway, and railroad law.
2. Conceptual intersection: The overlap or confluence of two legal doctrines, bodies of law, rights, or interests — as when criminal law and civil forfeiture "intersect," or when constitutional equal protection doctrine "intersects" with Title VII statutory claims.
The physical sense is the older and more technically precise legal usage. The conceptual sense is a modern analytical usage that has become standard in legal scholarship, judicial opinions, and encyclopedic legal writing.
Common Language
Modern common usage (Wiktionary): To cut into or between; to cut or cross mutually; to divide into parts. Also, of two sets, to have at least one element in common.
Historical common usage (Webster's 1913): To cut into or between; to cut or cross mutually; to divide into parts.
Editorial note: The common and legal meanings track closely in the physical sense. The gap emerges in the conceptual legal usage — when lawyers write that two doctrines "intersect," they mean something more structural than mere crossing: they mean that the application of one legal rule activates, complicates, or modifies the operation of another. This analytical sense has no direct counterpart in ordinary English usage and does not appear in historical dictionary definitions.
Common Confusion
In historical railroad and highway law, "intersect" had a precise technical meaning distinct from "run along," "parallel," or "cross at grade." Anderson's notes that a railroad running along a turnpike so as to require a change in the traveled path does not intersect the turnpike — it merely encroaches on or occupies the same corridor. Researchers reading historical right-of-way disputes, condemnation proceedings, or franchise grants should not assume that any physical proximity constitutes an intersection in the legal sense. The distinction controlled liability, compensation obligations, and statutory duties.
Why It Matters in Research
This term functions differently depending on the era and context of the source material a researcher is working with.
In historical sources (pre-20th century), "intersect" appears almost exclusively in its physical sense — railroad law, highway law, and property surveys. When a 19th-century statute or case uses the word, it is almost always describing a literal crossing of physical infrastructure, and the legal consequences (duties to construct crossings, liability for accidents, compensation for disruption) turned on whether an intersection technically occurred. Anderson's cautionary note — that mere alteration of the traveled path is not an intersection — reflects genuine litigation over this question.
In modern sources, "intersect" is used analytically to describe the relationship between legal fields or doctrines. When a court or encyclopedia says that criminal law and civil forfeiture "intersect," or that Title VII "intersects" with constitutional equal protection, it signals that a researcher needs to look at multiple bodies of law simultaneously and understand how each modifies the operation of the other. This usage is a research navigational cue, not a legal term of art with a fixed definition.
Researchers should be alert to the shift: a word search for "intersect" in historical databases will surface physical infrastructure disputes; the same search in modern legal scholarship or secondary sources will surface doctrinal overlap analysis. The two literatures rarely cross-reference each other, and conflating the usages can mislead a research strategy.
Historical Dictionary Support
Anderson's Dictionary of Law provides the most direct historical legal definition: "ordinarily, to cross." The entry is terse but usefully followed by an illustrative negative — a railroad running along a turnpike so as to require a change in the traveled path does not intersect it. This signals that Anderson understood "intersect" as requiring a true crossing, not merely an encroachment or a forced deviation. The physical precision of this definition was functionally important in railroad and highway franchise law, where statutory duties often attached only upon an intersection.
Anderson's entry does not address the modern conceptual usage at all, which is unsurprising for a 19th-century source. Historical dictionaries as a class are uniformly silent on the analytical sense of the term. Researchers relying solely on historical dictionaries to define "intersect" in a modern legal context will find the sources incomplete.
Webster's 1913 and Wiktionary both align with Anderson's physical definition, with Wiktionary additionally noting the set-theoretic sense (two sets sharing at least one element). That mathematical usage is the closest common-language analog to the modern legal analytical sense — two legal regimes "intersecting" when they share at least one operative domain — though legal writers rarely make this parallel explicit.
Encyclopedia Cross-Reference
The Law Mind Family Law Encyclopedia: Domestic Violence — Intersection with Custody and Visitation
The Law Mind Criminal Law Encyclopedia: Civil Forfeiture and Its Intersection with Criminal Law
The Law Mind Constitutional Law Encyclopedia: Title VII and Constitutional Intersections — Employment Discrimination and Equal Protection