Since the field of quasi contracts is not one of settled and precise limits, it is necessary, at the outset, to indicate just what part of the law of obligation this treatise is intended to cover. The term "quasi contracts" may with propriety be applied to all noncontractual obligations which are treated, for the purpose of affording a remedy, as if they were contracts. So interpreted, the subject includes: (1) judgments and other so-called contracts of record; (2) a number of official and statutory obligations, such as the official obligation of a sheriff to levy execution and pay over the proceeds, and the statutory obligation of the owner of a vessel to pay pilotage;1 and (3) obligations arising from "unjust whose example was followed by Professor Keener, included in this second class a number of customary obligations, such as that of the innkeeper and that of the carrier, which are not enforced, ordinarily, by means of contractual forms of action, enrichment," i.e. the receipt by one person from another of a benefit the retention of which is unjust. But in view of the fact that nearly all of the obligations included in the first two classes are commonly known and treated under more specific designations, or as parts of other clearly defined topics, while those of the third class have no other distinctive name whatever, it is believed that the term "quasi contracts," for the sake of convenience, should ordinarily be applied to obligations of the third class alone. For this reason, and for the further reason that they constitute a homogeneous group, essentially different from all others, this book will treat solely of obligations arising upon the receipt of a benefit the retention of which is unjust.

1 See Speake v. Richards, Hob. 206; Steamship Co. v. Joliffe, 1864, 2 Wall. (U. S.) 450. Professor Ames,