Unjust enrichment in law and equity

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In Moses v Macferlan, Lord Mansfield used money had and received, a common law money count, to provide relief in a case where an action’s outcome failed to align with the actor’s intention. In the First Restatement of Restitution, Warren Seavey and Austin Scott gathered together all cases, quasi-contractual and equitable, under the single principle that ‘a person who has been unjustly enriched at the expense of another is required to make restitution to the other.’ These two influential acts of fusion between common law and equity have caused a great deal of confusion in the scholarship and jurisprudence on unjust enrichment. With the fundamental differences between quasi-contract and equitable unjust enrichment obscured, scholars and judges have struggled to find the single principle or core case that unifies liability in what is now called the law of unjust enrichment. I argue that we can resolve the puzzles of unjust enrichment by rejecting the fusionist claims that started them all – that is, by distinguishing cases of quasi-contract (the common law money counts) from cases of equitable unjust enrichment – and by recognizing that each has a distinctive normative foundation. Quasi-contract, like other common law doctrines, is grounded in respect for the freedom and equality of agents conceived as beings with the capacity for free choice. Quasi-contract is concerned with the objective significance of external acts like requests and agreements on terms; it is not concerned with the frustration of the plaintiff’s particular purpose in acting. Equitable unjust enrichment, like other equitable doctrines that attend to mistakes, expectations, and intentions, is grounded in concern for individual autonomy. It recognizes that a court, as a public institution attuned to law’s self-imposability, cannot enforce an alienation of property with indifference to the way in which it may fail as an expression of the individual’s purposes and reasons for action.