(law) An assumption or undertaking by one person (the promisor) to perform an act for, or to pay a sum to, another person (the promisee), often without express agreement from the promisee to perform an act or remit consideration in return. An assumpsit is created, for example, when one person employs another without any written agreement as to compensation. In such an arrangement, the law will imply a duty to pay reasonable wages. An assumpsit also arises when one person receives money that belongs to another, in which event the law implies a duty to remit the sum to the owner.
(a) An express assumpsit is one in which the promisor states the assumption in distinct and definite language. A person who agrees to work for another on certain tasks for a specified time has made an express assumpsit.
(b) An implied assumpsit is one in which a promise is inferred by law from the conduct of a party or the circumstances of the case. If, without any express statement, a person begins working for another who knows and does not object to that work, a court may find that an implied assumpsit has arisen.
(c) An action in assumpsit is a court action to recover damages for breach of an oral or other informal contract. A seller who delivers goods to a buyer based on an oral contract and who does not receive payment may recover the proceeds in an action in assumpsit.