Although there are earlier cases in which obligations which would now be recognized as quasi contractual were enforced, Lord Mansfield's opinion in the case of Moses v. Macferlan,1 decided by the Court of King's Bench in 1760, may be said to mark the emergence of quasi contract as a distinct species of common law obligation. Some knowledge of the actions of debt and assumpsit is essential to an understanding of that opinion. Debt was a form of action that lay to recover a definite sum due by a record or a contract under seal or as the price of some thing or service; assumpsit, an action of later origin, lay to recover damages for the breach of such simple contracts as were not reached by the action of debt. In order to avoid the possibility of defense by wager of law,2 which was allowed in debt, attempts were made to use but which superficially resemble most contracts and differ from the duty not to commit a tort, in that they require the obligor to act rather than to forbear. See Ames, "History of Assumpsit," 2 Harv. Law Rev. 53, 64; Select Essays in Anglo-American Legal History, Vol. Ill, 259, 292 ; Keener, "Quasi-Contracts," p. 18. For a discussion of the distinction between quasi contracts and the duty not to commit a tort, see, post, Sec. 5.

1 2 Burr. 1005.

2 Wager of law was a method of trial. The oath of the defendant that he did not owe the debt, fortified by the oaths of a number (usually eleven) of his kinsmen and neighbors, called oath helpers or compurgators, that his oath was true, constituted a defense to the action. See Pollock and Maitland, "History of English Law," Vol. II, 600. 634. There is a reported instance of its use as late as 1824 (King v. Williams, the action of assumpsit in cases of simple contract to which debt applied. Eventually, by a process consisting of two distinct stages, this extension of assumpsit was accomplished. First, it was held that a preexisting debt constituted a consideration for a promise, and therefore, if one who was already under an obligation enforceable by an action of debt made a promise to pay the debt, such promise was enforceable by an action of assumpsit.1 Then, it was declared that a promise to pay a debt would be implied and it was therefore unnecessary to prove an express promise.2 Indebitatus assumpsit, as it was called, thus became a concurrent remedy in cases of debt upon a simple contract. This was the situation when Moses v. Macferlan3 arose. In that case, Moses had indorsed notes of one Jacob to Macferlan upon the latter's agreement that no suit should be brought against Moses on the notes. In violation of his agreement Macferlan had sued Moses upon his indorsements in the Court of Conscience4 and had obtained a judgment, the court taking the view that it had no jurisdiction over the collateral agreement not to sue which Moses had set up as a defense. Moses paid the judgment and then brought indebitatus assumpsit in the King's Bench to recover the money so paid. For the defendant, it was objected that since the case was neither one of a genuine promise by the defendant nor one to which the action of debt applied, the action of assumpsit would not lie. But Lord Mansfield, desirous of extending still further the scope of that simple and advantageous remedy, and finding his justification in the principles of the Roman law,5 declared that the objection was without merit, saying:6

2 Barn. & Cr. 538) and it was not formally abolished until 1833. See 73 Statutes at Large (3 & 4 Will. IV) c. 42, Sec. 13. In America the practice never obtained a foothold. See Childress v. Emory, 1823, 8 Wheat. (U. S.) 642, 675.

1 See Manwood v. Bruston, 1588, 2 Leo. 203, 204.

2 Slade's Case, 1602, 4 Coke, 92 b.

3 1760, 2 Burr. 1005.

4An inferior court for the collection of small debts.

5 See Appendix by Sir W. D. Evans to Pothier, "Obligations" (1806), Vol. II, 321-324; Scott,'.' Cases on Quasi-Contracts," pp. 9-16. 6 At page 1008.

"If the defendant be under an obligation, from the ties of natural justice, to refund, the law implies a debt, and gives this action, founded in the equity of the plaintiff's case, as it were upon a contract ('quasi ex contractu,' as the Roman law expresses it). . . . This kind of equitable action, to recover back money, which ought not in justice to be kept, is very beneficial, and therefore much encouraged. It lies only for money which, ex aequo et bono, the defendant ought to refund: it does not lie for money paid by the plaintiff, which is claimed of him as payable in point of honor and honesty, although it could not have been recovered from him by any course of law, - as in payment of a debt barred by the statute of limitations, or contracted during his infancy, or to the extent of principal and legal interest upon a usurious contract, or, for money fairly lost at play; because in all these cases the defendant may retain it with a safe conscience, though by positive law he was barred from recovering. But it lies for money paid by mistake; or upon a consideration which happens to fail; or for money got through imposition, (express or implied); or extortion; or oppression; or an undue advantage taken of the plaintiff's situation, contrary to laws made for the protection of persons under those circumstances. In one word, the gist of this kind of action is, that the defendant, upon the circumstances of the case, is obliged by the ties of natural justice and equity to refund the money."

Thus, by the device of a fictional promise, the door was opened to the enforcement of those obligations, previously unrecognized by the common law, which are now known as quasi contracts.