ABSTRACT

There are many situations in which a claim arises from the receipt of a benefit-for example, a claim

to reverse a mistaken or unauthorised transfer of money or property, or a claim for payment for

services conferred by mistake or in an emergency, or a claim for the surrender up of wrongfully

acquired benefits, or a claim for payment for the unauthorised use of property.2 Some such claims

historically formed a miscellaneous body of claims lying outside the recognised categories of the

common law-contract and tort-and were thought not to be capable of explanation in terms of

these categories. According to the theory of unjust enrichment,3 these various claims are based on

the principle of unjust enrichment.4 This is understood to be a principle equivalent to those that

underlie the traditional categories of law, for example the contractual principle that agreements

should be enforced, or the tortious principle that there is a duty to take reasonable precautions to

avoid causing harm to others.5 These underlying principles provide a guide to the development of

the law in a way that makes it more coherent, bringing together ostensibly different claims that

should be treated in the same way because they are based on the same principle, and eliminating

anomalies and unnecessary obscurity and complexity. The principle of unjust enrichment, it is

thought, promotes the development of a systematic and coherent body of rules analogous to those

of contract and tort, governing claims that arise from the receipt of a benefit.6 It is conceded that

the nature of the principle of unjust enrichment may be controversial and its scope imprecise. But

in this, it is argued, it is no different from the principles underlying contract or tort. These are by

no means uncontroversial, and sometimes controversy is reflected in arguments over the scope and

content of the law, but there is nevertheless sufficient clarity and consensus to provide a workable

principle and a recognised category.