Definition
A Latin phrase meaning "according to equity" or "in equity." Used in legal writing and argument to signal that a claim, remedy, or principle rests on equitable grounds rather than strict common law rules. The phrase invokes the authority of conscience and fairness as a basis for legal relief, distinct from rights enforceable purely at law.
Closely related is the companion phrase EX AEQUO ET BONO, meaning "according to what is just and good" or "according to equity and conscience." Where ex aequitate signals a grounding in equity generally, ex aequo et bono carries the stronger connotation of deciding a matter according to broad principles of justice and fairness rather than any formal legal rule — a standard sometimes invoked in arbitration and international law when parties expressly authorize a tribunal to depart from strict legal doctrine.
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Common Confusion
EX AEQUITATE and EX AEQUO ET BONO are related but not interchangeable. Ex aequitate simply locates a principle or remedy within the domain of equity. Ex aequo et bono goes further, authorizing decision-making by pure fairness independent of established legal rules. Black's 2nd Edition entry conflates the two under a single heading, which can mislead researchers into treating them as synonyms. They share a root concept but function differently in legal argument and in international arbitration contexts where ex aequo et bono has technical procedural significance.
The term also invites confusion with IN AEQUITATE, which similarly means "in equity" but appears less frequently in historical sources. The prepositional variation (ex versus in) does not produce a meaningful substantive difference; both phrases locate a matter within equity's domain.
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Why It Matters in Research
This phrase appears almost exclusively in older legal writing, arguments, and treatises — it is a term of historical legal Latin rather than modern usage. Researchers encountering it in primary sources from the seventeenth through nineteenth centuries should read it as a signal that the author is distinguishing equitable grounds from legal ones, often to argue for a remedy unavailable at common law.
The Black's 2nd Edition entry is notably compressed and typographically corrupted in digitized versions. The source line "Hee lib. 3, c@ 10, § 3" reflects OCR degradation of what is almost certainly a citation to Heeresbach or, more likely, to a civilian or equity treatise. Researchers relying on digitized versions of Black's 2nd Edition should be alert to such corruption throughout the Latin phrase entries, where special characters and abbreviations are especially prone to scanning errors.
Because the phrase signals equitable jurisdiction, documents using it connect directly to the historical divide between courts of law and courts of equity — a divide that shapes the structure of remedies doctrine through the merger of law and equity in modern federal and most state practice. Post-merger, the phrase retains historical significance but no longer marks a live jurisdictional boundary in most American courts.
In international arbitration, ex aequo et bono (the companion phrase) retains active technical meaning: tribunals empowered to decide ex aequo et bono are released from strict application of positive law. This remains relevant in investor-state and commercial arbitration contexts and distinguishes such clauses from standard choice-of-law provisions.
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Historical Dictionary Support
Black's 2nd Edition provides a minimal entry, pairing ex aequitate with ex aequo et bono and citing Blackstone's Commentaries (3 Bl. Comm. 168) for the latter. Blackstone uses ex aequo et bono to describe the civil law standard of equitable decision-making, contrasting it with the technical rigor of common law pleading. Earlier editions of Black's and contemporaneous legal dictionaries such as Bouvier's treat these Latin maxims as part of the general vocabulary of equity jurisprudence without extended analysis.
Historical sources uniformly agree that the phrase carries no independent doctrinal content beyond its directional function — it tells the reader that equity, not law, is the relevant framework. What historical dictionaries do not capture is the subsequent specialization of ex aequo et bono in international law and arbitration, a development occurring largely in the twentieth century and therefore outside the scope of nineteenth-century reference works.
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Jurisdictional Note
In U.S. federal courts and in most states that have merged law and equity, these phrases function as historical markers rather than jurisdictional signals. In international arbitration, ex aequo et bono retains operative force when expressly authorized by the parties or the governing arbitration rules.
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Encyclopedia Cross-Reference
The Law Mind Constitutional Law Encyclopedia: Ex parte Young — The Fiction That Permits Suits Against State Officers (for equitable relief doctrine in constitutional litigation context)
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