ABSTRACT
Throughout legal history, enthusiasm for unjust enrichment has tended to come in waves. The
same pattern has occurred several times. The idea is picked up and popularised; the more
analytically-minded step in to make it precise; briefly it is fashionable; and then, as the implications
of the analysis sink in, it falls from favour into a marsh of technicality. The transient dawn of
Dawson’s survey of ‘unjust enrichment’, composed in the 1950s, identified three major
outbreaks of the notion in the history of the West. We are now living through a fourth, on much the
same pattern. There was the initial wild enthusiasm in the 1960s and 1970s, as ‘unjust enrichment’
seemed to its supporters to provide the explanation for a wide range of doctrines. Then in the 1980s
the analytical lawyers stepped in, squeezing the slippery notion of unjust enrichment into a fairly
precise mould, the famous or infamous ‘taxonomic model’ of the subject. Inevitably, the decline
began in the 1990s, and still continues. Dawson’s moral is still true: once you remove the flexibility of
‘unjust enrichment’, you also remove the main emotional and moral reasons for supporting it. For the
last decade, the subject has become more and more technical; the theory once thought to explain so
much is acknowledged to explain less and less. The impenetrability of the debate to outsiders is a
commonplace of the conference circuit. And even those academics who devote themselves to the
subject full time complain about how hard it is to keep up with all the new writing. There is more and
Living through this rising tide of incomprehensibility, it is vital to remember essentials. The
taxonomic model of unjust enrichment is supposed to be a set of concepts explaining and
rationalising certain areas of that law. If it fails to do that, then it has no place in the law. If most
of the intellectual effort in the area goes into a-not conspicuously successful-attempt to reconcile
the theory with judicial holdings, then it is time to call it a day. If, by contrast, the taxonomic
approach gives great insights into the law, that would be a reason not only for retaining it, but for
extending its use. And if the increasingly complicated academic theory represents a deeper and
more sophisticated knowledge of the law, then undoubtedly this is a gain. The question is: which
are we dealing with here?
