Abstract. In this paper I argue that in contrast to the moral foundations of contract, tort, and the law of property, which are generally regarded as being aspects or elements of ‘right’, to put it in quasi-Kantian terms, liability to return the value of mistaken payments is an example of the law’s enforcing a duty of virtue. In a way similar (though not identical) to how the law might instantiate a duty of easy rescue as the ‘replacement’ in particular cases of the general duty of beneficence, liability for mistaken payments counts as an instantiation of the same duty of beneficence in a particular sort of factual situation. Accordingly, one of Birks’s most cherished theses – that the law of unjust enrichment is a distinctive aspect of private law, not to be assimilated to contract, tort, or the law of property – can be made out: it is distinctive in having an entirely different normative source, in virtue, not in right. But this result comes at a cost: (1)  a legal system could function more or less justly without a liability to return the value of mistaken payments; (2) Birks’s thesis that liability for mistaken payment is the archetype or paradigmatic case of liability for unjust enrichment would have to be abandoned; and (3) we would recognise that the liability to make restitution of mistaken payments falls under the category of policy-motivated justifications for restitutionary liability.

Bio. A graduate of the University of Western Ontario (B.SC Hons Genetics), the University of Toronto (LL.B), and Oxford (D.Phil), James Penner is Professor of Law and Vice Dean for Research in the Faculty of Law, National University of Singapore. Prior to joining NUS in 2013, Prof Penner taught at Brunel University, the London School of Economics, King’s College London and University College London. From 2011 to 2013 he served as Head of Department at the Faculty of Laws, UCL. He is a barrister of Lincoln’s Inn.

Professer Penner has written extensively on the law of trusts, private law more generally, and the philosophy of law, with special interests in the philosophical foundations of the common law, legal reasoning, and property theory. He is the author of The Idea of Property in Law and The Law of Trusts (now in its 9th Edition).