Definition
In civil law, expromissio is a form of novation in which a creditor accepts a new debtor in place of the original one, with the original debtor being fully released from the obligation. The transaction is complete upon the creditor's acceptance of the substitution — no consent from the original debtor is required. The new debtor (the expromissor) assumes the entire debt, and the old debtor walks away discharged.
This distinguishes expromissio from other debt-assumption arrangements in which the original debtor remains liable, either primarily or as a surety. Under expromissio, the release is immediate and absolute: there is no recourse against the prior obligor.
---
Common Confusion
Expromissio is closely related to but distinct from delegatio, another civil law mechanism for substituting a debtor. In delegatio, the original debtor typically participates in or initiates the substitution and may retain a role in the transaction. In expromissio, the new debtor approaches the creditor independently — the original debtor's cooperation is not required, and their release follows automatically from the creditor's acceptance. Both are species of novation by debtor substitution, but the procedural posture and the role of the original debtor differ. Researchers encountering either term in historical sources should not treat them as interchangeable.
---
Why It Matters in Research
Expromissio is a Roman and civil law term with limited direct application in modern common law jurisdictions, but it surfaces with some frequency in three research contexts:
First, in historical civil law materials — particularly sources drawing on Justinian's Corpus Juris Civilis and the civilian commentators — expromissio appears as part of a structured taxonomy of novation. Researchers working with Louisiana, Quebec, or other mixed or civil law jurisdictions may encounter it in older treatises, court opinions, or legislative commentary when the legal history of novation or debt assignment is under examination.
Second, because Black's Law Dictionary carried the definition forward through multiple editions with minimal elaboration, researchers relying solely on Black's may underestimate the term's doctrinal complexity. The Black's entries cite Bouvier's Institutes but say nothing about the distinction from delegatio or the doctrinal debate among civilians about whether expromissio required an express agreement or could be implied from conduct.
Third, in comparative law scholarship and in modern civil law jurisdictions that codified Roman-derived novation rules, expromissio (or its functional equivalent) may appear under different labels. French and Louisiana civilian doctrine, for instance, address the same mechanism under the broader heading of novation by substitution of debtor, without necessarily preserving the Roman terminology. A researcher searching only for "expromissio" in those sources may miss the substantive doctrine.
---
Historical Dictionary Support
Both Black's editions define expromissio identically and briefly: a species of novation by which a creditor accepts a new debtor, releasing the old. Both editions cite Bouvier's Institutes (no. 802) as authority. The second edition drops a reference to Webster that appears in the first, suggesting that by the second edition the editors no longer considered it a term with meaningful common-language standing.
The Black's definitions are accurate but thin. They capture the operative result — release of the original debtor upon acceptance of the new — but do not address the theoretical underpinning (the extinction of the original obligation and creation of a new one), the requirement of the creditor's affirmative consent, or the absence of any requirement for the original debtor's participation. These are features that matter when distinguishing expromissio from related concepts and that are addressed more fully in the civilian treatise tradition Black's gestures toward but does not reproduce.
Bouvier's Institutes, the cited authority, situates expromissio within a broader discussion of obligations and their extinction — a context that makes the term's doctrinal significance clearer than the dictionary entry alone conveys.
---
Jurisdictional Note
Expromissio as a formal legal category is largely confined to civil law and mixed jurisdictions. In common law systems, analogous outcomes — discharge of one debtor and substitution of another — are achieved through novation doctrine without resort to the Roman terminology. Louisiana courts and scholars are the most likely domestic American context in which the term or its direct civilian equivalent will be encountered.
---