ASSUMP'SIT (Lat. 3d pers. sing. perf. assumere, to undertake). The technical name of a form of action at common law. It was first used as a form of action on the case (see after the Statute of Westminster IL (1285), in which the plaintiff pleaded that the defendant undertook to perform some act by doing or giv ing something, the breach of which undertaking resulted in damage to the plaintiff. If the de fendant's promise or undertaking did not amount to the assumption of a common-law duty, a breach of which would be a tort (q.v.), it was necessary for the plaintiff to allege and prove that he had given consideration—that is, that he had given up a right or suffered a detriment in return for the defendant's promise—in order to show that lie had suffered damage. This was the origin of the modern doctrine of considera tion in the law of contracts. The action of as sumpsit is now limited as an action on contract, and as quite distinct from actions on the ease, notwithstanding their common origin. The term assumpsit is also applied in substantive law, though less frequently, to the promise, contract, or obligation of one against whom the action of assumpsit would lie. Express or special as sumpsit is the form of assumpsit brought to re cover damages for the breach of a bilateral contract, either express or implied in fact—that is, a contract in which the promise of one party to the contract is given in exchange for the promise the other, the mutual promises being expressed in spoken or written language, or im plied from the acts and conduct of the parties. It was not the proper form of action in which to recover on contracts under seal, the action in that case being in debt or covenant. Common,
general, or indcbitatus assumpsit is a form of assumpsit in which the use of that action was extended, for reasons now purely historical, so as to apply in nearly every case in which the common-law action of debt would lie. It was used to recover a liquidated sum of money. as distinguished from mere damages, as in an action to recover the purchase price of goods sold and delivered, or for money lent. The obligation to pay the liquidated sum may arise from con tract. express or implied; or, in the absence of contract, it may be an obligation imposed on the defendant. by law, aomethnes incorrectly terminal a contract implied in law, and known to modern legal writers as a quasi contract (q.v.). Thus. indcbitatus assumpsit was at common law the proper form of action in which to recover a penalty imposed by statute or money paid by mistake.
In modern times the use of this form of as sumpsit has been still further extended. so as to cover nearly all cases where the defendant is under an obligation to pay a sum of money to the plaintiff, even though unliquidated, pro vided the money is not payable as damages. The various forms of declaration in indebitalus us sumpsit were known as common counts (q.v.). The usual plea to the declaration in assumpsit is at common law non assumpsit, under which the defendant may give in evidence most defenses. Consult Could, 7'reatise on the Principles of Plemlitog in Civil Actions (Chicago, lS99).