We have constructive fraud, constructive trusts, constructive notice, and why not constructive contract, a contractual obligation existing in contemplation of law, in the absence of any agreement express or implied from facts? With this apology we shall use the term quasi contract as covering an obligation created by law and enforceable by an action ex contractu. We are not for the present interested in the circumstances which may give rise to this obligation as between individuals; nor as between an individual and a private corporation, or quasi public corporation, so-called, as a railroad or other public utility. In these cases the doctrine of unjust enrichment usually controls. Our inquiry relates to the conditions under which an individual may recover in implied assumpsit for money or property received from him by a municipal corporation and applied to municipal purposes under an invalid express contract-invalid for want of power to make the contract, or by reason of an irregular exercise of power. Does the fact that a municipality has been enriched at the expense of the individual, in such cases, give him a remedy in quasi contract?
Knowlton, Jerome C. "Quasi-Contractual Obligations of Municipal Corporations." Mich. L. Rev. 9, no. 8 (1911): 671-83.