Definition
Eign law is an archaic term for foreign law — the body of legal rules belonging to a jurisdiction other than the one in which a dispute is being heard. A court confronts eign law when a case involves parties, transactions, or interests connected to another state or nation whose legal rules differ from those of the forum. The term is rarely encountered outside historical legal texts; modern practice and scholarship use "foreign law" almost exclusively.
Common Confusion
Eign law should not be confused with alien law (rules applicable to non-citizen persons) or with the law of nations (what is now called public international law). Eign law in its historical usage is specifically the private law of a foreign jurisdiction invoked by the conflict-of-laws analysis of a domestic forum — a horizontal, court-to-court problem, not a question of citizenship status or international treaty obligation.
Why It Matters in Research
The term "eign law" functions primarily as a historical variant pointing toward what modern doctrine calls conflict of laws or private international law. Researchers encountering this term in older American or English sources should treat it as a direct synonym for "foreign law" in the conflict-of-laws sense and follow the trail into that larger body of doctrine.
The Bouvier entry cited here is fragmentary — it defines eign law by reference to the conflict-of-laws framework without completing the exposition — which is itself a research signal: the substantive doctrine was developed under "conflict of laws," not under "eign law," even in Bouvier's own era. A researcher who stops at the eign law entry will miss the full treatment.
Because the term drops out of use well before the twentieth century, it will not appear in modern statutory codes, federal or state court opinions after roughly the mid-nineteenth century, or contemporary secondary sources. Its usefulness is confined to reading historical materials — early American treatises, colonial-era pleadings, and English common law texts — where the variant spelling or phrasing appears.
Historical Dictionary Support
Bouvier's Law Dictionary provides the sole historical dictionary entry for this term in the Law Mind corpus, and that entry is notably incomplete: it defines eign law as arising when a case in one state involves foreign persons or interests and the domestic and foreign rules diverge, but breaks off with a cross-reference ("See —") rather than completing the definition. This incompleteness is instructive. Bouvier plainly regarded "conflict of laws" as the operative doctrinal home; "eign law" appears to function in his usage as a descriptive label for the phenomenon that triggers that analysis, not as a free-standing doctrine with its own rules.
No entry for "eign law" appears in Black's Law Dictionary or other standard sources in the corpus, reinforcing its status as an archaic variant rather than a term of art with independent doctrinal content. Historical sources are silent on any distinction between eign law and foreign law; the terms appear to be interchangeable.