on an implied promise, and (b) special or express assumpsit, founded on an express promise.See also Where a plaintiff brought assumpsit in lieu of debt sur contract, it was necessary for the plaintiff to specify how the antecedent debt had arisen. It was insufficient for the plaintiff to merely allege that, being indebted, the defendant promised to pay. This gave rise to the "common counts": common ways of pleading how the debt arose. It is important to note that where assumpsit was brought in lieu of debt, the plaintiff's action was for a liquidated sum. In contrast, where a plaintiff brought special assumpsit, the action was for an unliquidated sum assessed by the civil jury. Examples of the common counts include: For goods sold ("quantum valebant"); For work done ("quantum meruit"); For money lent; For money due on an account stated; For money laid out to the use of the defendant; and For money had and received to the defendant's use. By the 18th and 19th centuries, the action of assumpsit was used to enforce both contractual and quasi-contractual claims. The recognition in Slade's Case that the law would import or imply a promise to pay the debt paved the way for other implications. In some cases, such as actions for a reasonable remuneration for services provided to the defendant at the defendant's request (a quantum meruit), the implication might be a true reflection of reality. If so, in modern terms, this is simply an action in contract for breach of an implied term. In other cases, however, the implication of a promise to pay was wholly fictitious. For example, where A mistakenly paid money to B, A would bring an action for money had and received to the defendant's use. In such a case, the law would imply a promise by B to pay the debt. In modern terms, this is an action in unjust enrichment: B is enriched by the receipt of money at the expense of A in circumstances which are 'unjust' (viz., that A's intention to benefit B is vitiated by the mistake). Abolition of the forms of action The Common Law Procedure Act 1852 abolished the common law forms of action in England and Wales. Furthermore, assumpsit as a form of action became obsolete in the United Kingdom after the passing of the Judicature Acts of 1873 and 1875. In the United States, assumpsit, like