Ripley v. Fitch

Determined by the court — That under this issue the defendant cannot give in evidence payment of the note; this would be to surprise the plaintiff, when he comes prepared only to prove the promise. The defendant by undertaking to prove payment, admits, that he did promise contrary to his plea; and to show that he is discharged from it, by having performed it. The distinction is, that in an implied promise payment may be given in evidence under the plea of non-assumpsit, for that extinguishes the promise, whichi continues no longer than the duty subsists, but in an express promise, both reason and the law is otherwise. The defendant moved for liberty to alter his plea, and to plead full payment; which was allowed by the court. The cause was afterwards referred.