A quasi-contract is a fictionalcontract recognised by a court. The notion of a quasi-contract can be traced to Roman law and is still a concept used in some modern legal systems.
History
In common law jurisdictions, the law of quasi-contract can be traced to the medieval form of action known as indebitatus assumpsit. In essence, the plaintiff would recover a money sum from the defendant as if the defendant had promised to pay it: that is, as if there were a contract subsisting between the parties. The defendant's promise—their agreement to be bound by the "contract"—was implied by law. The law of quasi-contract was generally used to enforcerestitutionaryobligations. The form of action known as indebitatus assumpsit came to include various sub-forms known as the common money counts. The most important of these for the later development of the law of quasi-contract included: actions for money had and received to the plaintiff's use; actions for money paid to the defendant's use; quantum meruit; and quantum valebat. Quasi-contractual actions were generally used to remedy what would now be called unjust enrichment. In most common law jurisdictions the law of quasi-contract has been superseded by the law of unjust enrichment.
Quasi-contract and contract
A quasi-contract was distinct from a contract implied in fact.
Contract implied in fact. A person's assent to be bound by an agreement can be expressed or implied. In the latter case, assuming the requisite formalities for a valid contract are met, there is a perfectly normal contract. The only distinction between a contract arising by express agreement between two people and a contract implied-in-fact is that the latter was recognised by a court drawing inferences from facts proved at trial. When the plaintiff sued on either sort of contract, she was suing in the law of contract in respect of a consensually assumed obligation and her remedy for the defendant's breach was damages.
Quasi-contract. In contrast, quasi-contract refers to situations in which a defendant is bound as if there were a contract. When the plaintiff sued on such a 'contract' by bringing an action of indebitatus assumpsit, she was not enforcing some consensually assumed obligation, but rather an obligation imposed by law.
