acted vi et armis contra pacem regis (with force and arms against the King's Peace). This action became known as trespass on the case. To bring the claim within trespass on the case, the plaintiff would characterise the defendant's breach of agreement as a wrong. During the 15th century, the received learning was that an action on the case did not lie for mere inaction ("nonfeasance"). By the beginning of this 16th century, this was no longer the case. Provided a plaintiff could show that the defendant was guilty of misfeasance, deceit, or the plaintiff had made a pre-payment, the plaintiff could bring assumpsit for nonfeasance. By the beginning of the 16th century lawyers recognised a distinct species of action on the case known as assumpsit, which had become the typical phrase in the pleadings. Assumpsit in lieu of debt The question that arose in the 16th century was whether assumpsit could be brought in lieu of debt. For a plaintiff, assumpsit was the more desirable course: the defendant would not be able to elect to wage his law as he would in debt sur contract. In order to bring assumpsit, the plaintiff would plead that, the defendant being indebted to the plaintiff, the defendant had later promised to pay the debt. In short, the plaintiff would separate the existence of the debt (which generated an action of debt sur contract) from a promise to pay the debt (which would generate an assumpsit for nonfeasance). This form of pleading gave rise to the name of the action: indebitatus assumpsit. The practice of the King's Bench and the Court of Common Pleas differed during the course of the 16th century. In the King's Bench, it was not necessary for the plaintiff to prove the subsequent promise. The Common Pleas disagreed. Matters came to a head in Slade's Case in 1602. The case effectively established that assumpsit could be used in lieu of debt: the law would imply a promise to pay the debt from the existence of the debt itself.Slade's Case effectively put an end to the use of debt sur contract, and with it wager of law. Of course, it was not possible to bring assumpsit where the proper action was debt sur obligation (that is, debt on a deed or bond). Common counts Claims in actions of assumpsit can be divided into: (a) common or indebitatus assumpsit, brought usually