Mistaken Payments, Quasi-contracts, and the ‘Justice’ of Unjust Enrichment

The law of unjust enrichment has often been described as the law of events materially identical to a mistaken payment. By this, lawyers often mean that the cause of action in unjust enrichment is somehow shaped and grounded by the reason why the recipient of (some) mistaken payments morally ought to refund the payor. The difficulty, however, is that the normativity of mistaken payments remains a challenge to explain. This article aims to reinvigorate the view that the moral duty to return mistaken payments is grounded by a tacit agreement between the payor and payee that the payment was conditional (coupled with the failure of that condition). To do so, it critically examines the ways in which our intentions can be conditioned, and how those conditions are communicated in our agreements. The article concludes by examining what implications a conditions-based understanding might have for the law of unjust enrichment.