Quasi-contract
A fictional contract imposed by law to prevent unjust enrichment.
Last updated
A quasi-contract, also called an implied-in-law or constructive contract, is a court-created legal fiction. Its origins lie in Roman law, and it continues to appear in some modern legal systems. The doctrine is based on the Roman principle that no one should become wealthy at another’s expense.
History
In common law, the idea of a quasi-contract grew out of the medieval legal action known as indebitatus assumpsit. Under this action, a plaintiff could recover money from a defendant as if the defendant had promised to pay it—as if a real contract existed. The defendant’s agreement was implied by law, not by actual consent. This area of law was mainly used to enforce restitution.
The indebitatus assumpsit action developed several sub-forms, called common money counts. The most important for the later law of quasi-contract were: (i) money had and received for the plaintiff’s use; (ii) money paid for the defendant’s use; (iii) quantum meruit; and (iv) quantum valebant. These quasi-contractual claims were generally used to remedy what is now called unjust enrichment. In most common law systems, the law of unjust enrichment has since replaced the law of quasi-contract.
A quasi-contract is different from a contract implied in fact, and from an express contract. In a contract implied in fact, a person’s agreement to be bound can be shown by conduct rather than words.
If the required formalities are met, this is still a normal contract. The only difference from an express contract is that the court infers the agreement from proven facts. When a plaintiff sues on either an express or an implied-in-fact contract, they are enforcing a consensual obligation, and the remedy for breach is damages.
In contrast, a quasi-contract binds a defendant as if there were a contract. When a plaintiff sues using indebitatus assumpsit, they are not enforcing a consensual obligation. Instead, they are enforcing an obligation imposed by law.
Last updated 2026-09-30 from the source article.
Quick Facts
- Field
- Law
- Known for
- Fictional contract recognized by a court to enforce restitutionary obligations
- Origin
- Roman law
- Related doctrine
- Nemo debet locupletari ex aliena jactura (no one should grow rich out of another's loss)
- Common law origin
- Medieval form of action indebitatus assumpsit
Facts from the source article.
Lore & Background
In common law jurisdictions, the law of quasi-contract traces to the medieval form of action known as indebitatus assumpsit. Under this form, a plaintiff would recover a money sum from the defendant as if the defendant had promised to pay it—that is, as if a contract existed. The defendant's promise was implied by law, and quasi-contract was generally used to enforce restitutionary obligations. The form of action indebitatus assumpsit came to include various sub-forms known as the common money counts, including actions for money had and received to the plaintiff's use, money paid to the defendant's use, quantum meruit, and quantum valebant.
Quasi-contractual actions were generally (but not exclusively) used to remedy what would now be called unjust enrichment. A quasi-contract is distinct from a contract implied in fact. In a contract implied in fact, a person's assent to be bound is inferred from facts proved at trial, but it remains a consensual obligation. In contrast, a quasi-contract binds a defendant as if there were a contract, but the obligation is imposed by law, not by consent.
Reader's Guide
The significance of quasi-contract lies in its role as a legal fiction that allows courts to impose obligations to prevent unjust enrichment, even when no actual agreement exists between parties. Originating in Roman law and developed through the common law action of indebitatus assumpsit, it provided a mechanism for restitution that did not rely on the plaintiff proving a consensual contract. The doctrine's core principle—that no one should profit from another's loss—remains influential.
In most common law jurisdictions, the law of quasi-contract has been superseded by the law of unjust enrichment, but its historical development shaped modern restitution law. The distinction between quasi-contract and implied-in-fact contract highlights the difference between obligations imposed by law and those arising from actual (though unexpressed) consent. Understanding quasi-contract is essential for grasping the evolution of restitutionary remedies and the boundaries between contract and unjust enrichment.
Frequently Asked Questions
What is a quasi-contract?
A quasi-contract is not a real agreement between parties but a fictional one that a court imposes to force one person to pay restitution to another. It is sometimes called an implied-in-law or constructive contract.
Where does the quasi-contract concept originate?
The idea stretches back to Roman law, where courts recognized obligations that felt contract-like even though no actual deal was struck. In common-law jurisdictions, it evolved through the medieval action known as indebitatus assumpsit.
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Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Quasi-contract (CC BY-SA 4.0).
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