A quasi-contract (also called an implied-in-law contract or constructive contract) is not a contract in the true sense. There is no offer, acceptance, or mutual intent to be bound. Instead, courts construct the obligation as a remedial device to reverse unjust enrichment — the principle that a person who receives a benefit at another's expense, under circumstances making retention inequitable, must pay its reasonable value.
The doctrine traces back to Roman law's quasi ex contractu obligations and was absorbed into English common law through cases such as Moses v. Macferlan (1760), where Lord Mansfield grounded the action in the idea that the defendant was bound "by the ties of natural justice and equity to refund the money." Modern U.S. doctrine is summarized in the Restatement (Third) of Restitution and Unjust Enrichment (2011).
To recover, a claimant typically must show:
- A benefit conferred on the defendant by the plaintiff;
- The defendant's knowledge or appreciation of that benefit; and
- Retention of the benefit under circumstances that would be unjust without payment.
The usual remedy is quantum meruit ("as much as he deserved") for services or quantum valebant for goods — measured by the reasonable market value of what was provided, not by any agreed price (since none exists).
Quasi-contract is unavailable where an enforceable express contract already covers the same subject matter, and it generally will not aid a plaintiff who conferred a benefit officiously (a volunteer) or as a pure gift. Common factual settings include emergency medical services rendered to an unconscious patient, mistaken payments to the wrong recipient, and work performed under a contract later found void or unenforceable (for example, under the Statute of Frauds).
In civil-law systems, analogous doctrines appear under gestion d'affaires (negotiorum gestio) and enrichissement sans cause in the French Civil Code, and §§ 812–822 of the German Bürgerliches Gesetzbuch (BGB) governing ungerechtfertigte Bereicherung.
Example
In Cotnam v. Wisdom (Arkansas Supreme Court, 1907), physicians who treated an unconscious streetcar-accident victim who later died were allowed to recover the reasonable value of their services from his estate on a quasi-contract theory, even though the patient never agreed to treatment.
Frequently asked questions
An implied-in-fact contract is a real agreement inferred from the parties' conduct and shows genuine mutual assent. A quasi-contract has no assent at all — the court imposes the obligation by law to prevent unjust enrichment.
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