Classification and Unjust Enrichment
| DOI | http://doi.org/10.1111/j.1468-2230.2004.00521.x |
| Published date | 01 November 2004 |
| Date | 01 November 2004 |
| Author | Peter Jaffey |
REVIEWARTICLE
Classi¢cation and Unjust Enrichment
Peter Ja¡ey
n
Peter Birk s,Unjust Enrichment, Oxford:Oxford UniversityPress, 2003, xxxþ274 pp,
pb d25.00.
INTRODUCTION
One of the most striking changes in academic research and teaching in recent
times has been the appearance of a new subject under the name of restitution or
unjust enrichment. This has transformed the treatment of various areas of the
common law that were historically neglected, confused and obscure, and has
had, overa relatively short period, a marked e¡ect on the approach of some judges
to these areas. One of the most in£uential works has been Peter Birks’s An Intro-
duction to the Law of Restitution,
1
originally published nearly twenty years ago.
Much of the literature has been concerned with exploring issues identi¢ed by
Birks, in the terminology and accordi ng tothe general approach that he adopted.
Birks has been in£uential not only through this book and the numerous articles
and other books that developed and modi¢ed h is views, but also through scholar-
ship that he has facilitated and promoted: important work has been produced by
his research students and by participants in academic seminars and conferences
organised by him. In addition, the Restitut ion Law Review, which Birks helped to
found, has provided a new forum for the promotion and discussion of these
developments.
Given the passage of time and the volume of literature, it is not surprising that
Unjust Enrichment
2
revealssome signi¢cant changes from the approach originally
taken in An Introductionto the Law of Restitution. But the newbook is acontribution
to the same general project, which is to bring together into a single body of law
various claims that were historically separated and unrelated; in other words, to
establish restitution or unjust enrichment as a category of law analogous to the
traditional categories of contract and tort.
The fundamental issue that this project raises is classi¢cation: what it means
to say that there is a category of unjust enrichment law, and why it is important.
This review will concentrate on this question. It will examine Birks’s scheme of
n
Law Department, BrunelUniversity. I amgrateful to a number of people for their comments on a
draft of this article:David Campbell, Dennis Klimchuk, Hanoch Dagan,Mahmood Bagheri and Tony
Ja¡ey.
1 P. Birks, AnIntroduction to the Law of Restitution(Oxford: OxfordUniversity Press, rev edn1989).
2 P. Birks, Unjust Enrichment (Oxford: Oxford University Press, 2003). References are to this book
unless otherwise stated.
rThe Modern LawReview Limited 2004
Published by BlackwellPublishing, 9600 Garsington Road,Oxford OX4 2DQ,UK and 350 Main Street, Malden, MA 02148, USA
(200 4) 67(6) MLR 1012 ^1031
classi¢cation and the nature of his category of unjust enrichment, and its relation
to other categories such as contract and property.This will involve concentrating
mainly on Parts 1 and 3 of Unjust Enrichment. Part 1 has a chapter on Birks’s ‘core
case’ of unjust enrichment and a chapter on classi¢cation. These chapters explain
his general approach to private law and unjust enrichment and propound a
scheme of classi¢cation, aversion of which ¢rst appeared in An Introduction to the
Law of Restitution.
3
Part 3 considers what counts as ‘unjust’ in Birks’s theory of
unjust enrichment. This reveals a signi¢cant change in Birks’s thinking, the move
from the theory of ‘unjust factors’to the theory of ‘no legal basis’.
Birks’s discussion of his scheme of classi¢cation in Part1 is not just a prelimin-
ary rhetorical £ourish or a gesture at theory. It is at the heart of the project of
showing that a rational understanding of private law requires the recognition
of a category of unjust enrichment. Birks has always emphasised the importance
of classi¢cation. Rightly, in my view, he has always insisted that the very use of
concepts in reasoning, in the lawas elsewhere, necessarily involves some form of
classi¢cation; without it we are faced with an incomprehensible mass of particu-
lars.
4
But there are di¡erent types of classi¢cation, and it is argued below that
Birks’s scheme relies on a form of classi¢cation that is not appropriate for his pro-
ject. I shall start with a discussion of classi¢cation in general, as a prelude to adis -
cussion of Birks’s scheme.
CLASSIFICATION IN THE LAW
Justi¢catorycategories
The ¢rst of the two types of classi¢cation discussed here is classi¢cation by ‘justi-
¢cation’, or classi¢cation into ‘justi¢catory categories’. This can be understood as
follows.Where the law is settled, the determination of the legal position involves
simply identifying an authoritative rule that uncontrovertibly applies to the facts
in issue. In other cases there maybe no authoritative applicable rule, or there may
be uncertaintyabout whethera rule applies. It is not easyto give an uncontrover-
sial account of legal reasoning in such cases. I think it would be conventional to
say that the judge makes his determination by ‘analogical reasoning’, ie by draw-
ing on principles underlying other rules that are not actually applicable to the
facts.
5
On one view, this should be understood as part of a broader exercise in
determining what relevant rule is prescribed by the theory that adequately
3 Aboven 1,20^23.The second dimension of Birks’sclassi¢catory grid consists of ‘responses’,includ-
ing ‘restitution’, ‘compensation’ and ‘punishment’. Birks contrasts a response with the causative
event that gives ri se to it. For reasons of space I have not discussed restitution as a remedy or
response or the i ssues of ‘multi-causality’ and quadration.
4 See eg P. Birks,‘Rights, wrongs and remedies’(200 0)20 OJLS 1^3.
5 See eg N. MacCormick, Legal Reaso ning a nd L egal Theory (Oxford: Oxford University Press, rev
edn, 1994) ch 7; C. R. Sunstein, ‘OnAnalogical Reasoning’ (1992) 106 Harv LR 741; J. Raz, ‘Law
and Value in Adjudication’, i nThe Authorityof Law (Oxford: Oxford University Press, 1979). This
may lead to the assimilation of di¡erent rules i nto a single rule covering matters that were pre-
viously understood to be governed by di¡erent rules; or it may be used to justify breaking down
a rule into two distinct rules.
Peter Ja¡ey
1013rThe Modern LawReview Limited 2004
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