Unjustified enrichment: surveying the landscape
Preliminary questions ‘Unjustified enrichment’. The expression is mysterious. So are the other terms in use for the same subject, ‘unjust enrichment’ and ‘restitution’. What is an enrichment and when is it unjustified? To state that something amounts to unjustified enrichment is merely a conclusion, that because the enrichment is unjustified it should be returned, restored or made over to the person properly entitled to it. That conclusion is in need of supporting normative argument. But what sort of argument? Some time ago the Roman jurist Pomponius wrote the now-famous words nam hoc natura aequum est neminem cum alterius detrimento et iniuria fieri locupletiorem , ‘by the law of nature it is right that nobody should be unjustly enriched at another's expense’. Pomponius's maxim encapsulates the key elements of enrichment liability: enrichment, which is unjust, and which is at the expense of the claimant. But it exemplifies a problem that faces modern legal systems, too: formulating the principles of a law of unjustified enrichment in a way which is clear and yet not excessively broad. There is no doubt that Pomponius's formulation is, as a matter of classical Roman law, much too broad. There were many cases in which unjustified enrichment was simply allowed to rest where it arose. A clear instance is the claim of a possessor in good faith who improved land from which he was later ejected by the true owner.
The Scope and Structure of Unjust Enrichment
From the publication of his Introduction to the Law of Restitution in 19851 until his death in 2004, Peter Birks was the leading common law scholar of the law of restitution and unjust enrichment. He contributed more than anyone else to shaping the subject and setting the agenda for the ever-growing body of academic scholarship dedicated to it. Birks’s work established on several points the views against which others are articulated and defended. So it was dramatic when he announced in the preface to the first edition of Unjust Enrichment (published in 2003) that ‘[a]lmost everything of mine now needs calling back for burning.’2 Now, this overstates the breadth of the changes in Birks’s view that it prefaces. But the three principal recantations of Unjust Enrichment, as Birks calls them, are significant and deep. In answer to the commentary attracted by its publication and to developments in case law, Birks quickly set to preparing a second edition, which he left nearly complete at the time of his death in July 2004. The second edition of Unjust Enrichment represents Birks’s last words on the subject. Readers of the first edition will need to review the second. There are important developments of parts of the analysis, and one recantation is reconsidered (though not recanted). It is required reading for everyone else interested in this fascinating area of law. Birks’s exposition and analysis are, as always, unparalleled in clarity and rigour. The first part is an especially accessible introduction to the law of unjust enrichment and to what is at issue in the claim that there is such a domain of private law. As it travels through the details and into less settled areas of the law, the book asks more of the reader; but that work is amply repaid. Unjust Enrichment is a first-rate work. I
Choice of Law Rules in Claims of Unjust Enrichment
A certain dancer named Paris paid Nero's daughter, Domitia, a large sum of money to be manumitted. He discovered later that he had never been a slave and that the manumission was unnecessary—a curious oversight. Although the court allowed him to recover his money, he remarked"—bitterly one would imagine—that no one had asked Domitia whether she had known that he had been a freeman when he was manumitted. This enrichment claim from antiquity involves the famous and hints at imperial corruption. Most cases are more prosaic: overpayment of an account, delivery to the wrong person, unauthorised use of property and so forth. One person has benefited at the expense of another. The rules of unjust enrichment, generally speaking, are designed to undo errors, misconceptions and mistakes that bedevil our activities no matter how carefully we try to avoid them.