Unjust Enrichment

The law of unjust enrichment is something of a lost child in every legal system. In a wide range of situations, the law requires that a defendant who has been enriched at the expense of a plaintiff make restitution to that plaintiff, either by returning the very substance of the enrichment, or, more often, by repaying its monetary value. But only if the enrichment is unjust, or unjustified: a gift, for example, is a justified enrichment. This generic description of the scope of the subject can hardly give an inkling of the range of situations in which it plays a role. Some examples include the payment of money by mistake, as when a debtor pays more than they actually owe; improvements to another person’s property, whether or not caused by a mistake regarding ownership; the payment of another’s debt; and the work done by a partner, perhaps over many years, in a cohabitational relationship. This wide range of operation leads us immediately to see one of the most striking examples of diversity among modern legal systems in a field of basic private law. At one extreme—as in, on some views, the modern common law—all or almost all of the law of unjust enrichment has been conceptually unified into a single legal category. At the other extreme—as in Roman law and the old common law, but also as in modern French and Quebec law, and also Jewish law—we see instead a miscellany, a multitude of single instances, particular claims or actions which address particular difficulties. Especially in uncodified systems, whether common law or civil law, the question whether a unified or disaggregated approach is more appropriate is one of the live issues of the early twenty-first century. The law of unjust enrichment, then, is a concrete example of the intellectual phenomenon that sets lumpers against splitters and hedgehogs against foxes. Many are the debates about terminology, classification, and taxonomy in this field of law. One example will suffice. The defendant and the plaintiff make a contract by which the plaintiff is to pay $100 in advance and the defendant will repair the plaintiff’s damaged painting. The money is paid but then the painting is stolen; this renders the contract impossible of performance, and brings it to an end. The plaintiff can get his money back. In German law, this is a claim in unjust enrichment. In French law, this case was not expressly dealt with by the Civil Code until the reform of 2016; now, as in Quebec since 1994, the Code recognizes it as a claim for restitution, but not one founded on unjust enrichment. In the common law, torn between the dictates of history and the systematizing efforts of twentieth century jurists, it might be a claim based on a “total failure of consideration,” or it might be a claim in unjust enrichment, depending upon whom one asks. In common law and civil law alike, this branch of the law is often ascribed to equity; and in the common law, even the claims that were recognized in the courts of common law, before the fusion of common law and Equity, were characterized as equitable by the common law judge, Lord Mansfield. This is because the law of unjust enrichment has a mission of fixing what would otherwise be unjust. But it is more than that: it is also the case that much of the law of unjust enrichment seems to be about fixing injustices that the law itself is in danger of creating. One reflection of this is that there is no corresponding field of inquiry in moral philosophy. …