Written by attorneys · grounded in primary & secondary sources — see below
A historical legal phrase denoting treatment according to equitable principles rather than strict legal rules.
Sources & Authorities· 12 primary sources
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Cases
Statutes
Uniform Acts
How it applies
Common Examples
6
Equal Parent-Child Status in Succession
Isabelle Inman and her partner never married but raised two children together. After Isabelle died intestate, the probate court applied in aequo principles to recognize both children as her heirs with full rights under the uniform probate rules, allowing them to inherit equally without regard to the parents' marital status.
Equitable Division of After-Acquired Collateral
Lender Bank and Borrower Corp disputed priority in commingled inventory. Although a later security interest was perfected first, the court applied in aequo principles to rank the interests equally in proportion to collateral value at the time of commingling.
Penn Central Transportation Co. et al. v. New York City438 U.S. 104, 98 S.Ct. 2646, 57 L.Ed.2d 631 (1978)
Equitable Review of Agency Procedure
Icarus Aviation challenged new nuclear safety regulations. The court applied in aequo equitable standards to determine whether the agency had considered all relevant factors before upholding the rules.
Vermont Yankee Nuclear Power Corp. v. Nat. Res. Def. Council, Inc.467 U.S. 837, 843, 104 S. Ct. 2778, 2781, 81 L. Ed. 2d 694 (1984)
Equitable One-House Veto Analysis
Irene Ingalls faced deportation after a legislative veto. The court applied in aequo principles to require bicameral action and presentment rather than strict procedural rules.
Immigration & Naturalization Service v. Jagdish Rai Chadha462 U.S. 919, 954 n. 16, 103 S.Ct. 2764, 2785 n. 16, 77 L.Ed.2d 317
Equitable Liberty Interest Review
Ibrahim Iqbal sought physician assistance to end terminal illness. The court applied in aequo equitable principles to weigh fundamental liberty interests against state prohibition rather than rigid due-process rules.
Washington v. Glucksberg521 U.S. 702 (1997)
Equitable Marital Privacy Analysis
Isabella Ingram and her husband sought contraceptives banned by state law. The court applied in aequo principles to protect marital privacy as an equitable interest beyond strict statutory text.
Griswold v. Connecticut381 U.S. 479 (1965)
Common questions
Frequently Asked
2
What does the Latin phrase in aequo signify in historical legal usage?+
It refers to adjudication or treatment according to principles of equity rather than rigid common-law rules.
How does in aequo differ from ex aequo et bono?+
In aequo simply means in equity. Ex aequo et bono refers to deciding a dispute according to what is fair and good, even without strict legal authority.
5 U.S. (1 Cranch) 137 (1803)Property
…of State, therefore, being in the same situation as to these duties as every other ministerial officer of the United States and equally liable to be compelled, is also bound by the same rules of evidence. These duties are not confidential but public and his clerks have no exclusive privileges except as to facts concerning…
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