Equity has long allowed a person who pays money to another under the mistaken belief a valid contract exists to recover that money when the contract is subsequently canceled for fraud or mistake and the rights of innocent parties have not intervened. In cases where the tortfeasor has benefitted by his wrong, the plaintiff may elect to waive the tort and bring an action in assumpsit for restitution. Such an action arises out of a duty imposed by law devolving upon the defendant to repay an unjust and unmerited enrichment. A constructive trust is one that arises by operation of law against one who, by fraud, wrongdoing, or any other unconscionable conduct, either has obtained or holds legal right to property which he ought not to, in equity and good conscience, hold and enjoy. A constructive trust is an appropriate remedy against unjust enrichment.
Unjust enrichment is an essential fact in nearly every case where a constructive trust is imposed.
The proper basis for impressing a constructive trust is to prevent unjust enrichment. Where a person wrongfully disposes of property of another knowing that the disposition is wrongful and acquires in exchange other property, the other is entitled to enforce a constructive trust of the property so acquired. An equitable lien is a creature of equity based on the equitable doctrine of unjust enrichment, and is a right to have a fund or specific property applied to the payment of a particular debt. A general doctrine of equity permits imposition of an equitable lien where the claimant's expenditure has benefited another's property under circumstances entitling the plaintiff to restitution. Where debts or claims against property are paid in good faith by another on the express or implied request of the owner of the property, the one so paying is entitled to an equitable lien on the property for his reimbursement.