5 Restitution: A New Start ? LIONEL SMITH * I. Th e Problem In my view, something has gone wrong in the law of restitution for unjust enrichment. In this chapter, I aim to explain what I think has gone wrong, and to propose the beginning of a solution. Th e fi rst part aims to describe the problem and why it is a serious one. Th e second part off ers the beginning of a way forward. Private law in the common law is oriented around causes of action. Causes of action are normative packages that justify liability. Th e phrase ‘ cause of action ’ is actually quite ambiguous and in my view has three distinct meanings or senses.1 Th e fi rst meaning is the most abstract and general. An example of it is in the sentence, ‘ the cause of action in battery consists of the intentional infl iction upon the body of another of a harmful or off ensive contact ’ . 2 Th is is a statement that if any conduct occurs that fi ts this general description, a claim will arise (subject to defences). Th e second meaning focuses on facts. It is oft en found in judicial defi ni- tions, like this one: A cause of action has traditionally been defi ned as comprising every fact which it would be necessary for the plaintiff to prove, if disputed, in order to support his or her right to the judgment of the court. 3 On this defi nition, a cause of action is not a general statement but a collection of particular facts that have happened. Th is defi nition is important when, for exam- ple, you have to know where or when a cause of action arose, as you might for * I thank Professor Robert Stevens for sharing many ideas, in particular from his recent unpublished work. I also thank Professor Peter Devonshire and Mr Rohan Havelock for their kind invitation to and hospitality at the Faculty of Law, University of Auckland on 18 – 19 September 2017, where a version of this chapter was presented. 1 For a fuller argument, see L Smith , ‘ Defences and the Disunity of Unjust Enrichment ’ in A Dyson , J Goudkamp and F Wilmot-Smith (eds), Defences in Unjust Enrichment ( Oxford , Hart Publishing , 2016 ) 27 . In the current chapter I discuss the common law, but the earlier paper looks at this question comparatively and notes that civilian systems have an approach that is not dissimilar. 2 S e e Bettel v Yim ( 1978 ) 20 OR (2d) 617 (Ontario County Court) 621. 3 Danyluk v Ainsworth Technologies Inc 2001 SCC 44 , [2001] 2 SCR 460 [54]. 88 Lionel Smith jurisdictional reasons or in relation to concerns about the limitation of actions. Th e third and fi nal meaning is also particular: a lawyer might say, ‘ you have a cause of action in libel against that publisher ’. She is not referring to a general proposition about how liability can arise (the fi rst sense), nor to a set of facts (the second sense). She is saying that because certain facts have occurred (a cause of action in the second sense), those facts, when combined with a general rule (a cause of action in the fi rst sense), create a claim by this particular plaintiff against this particular defendant. Her claim is thus both normative and very particular: that defendant is liable to this plaintiff . My concern is with the fi rst sense: general statements of the conditions on which claims will arise. A cause of action in this sense exists to protect something valuable, something we consider worthy of protection. Th e cause of action in libel protects our reputations, while the cause of action in battery protects our bodily integrity. Th ose are usually treated as diff erent rights that we have, founded on diff erent aspects of personality that are worthy of protection. Th is is why commit- ting the tort of libel is diff erent from committing the tort of battery. Th is explains why the defences to the two are diff erent, and why a battery is much more likely to be a crime than a libel. Other causes of action may be founded on constitutional values, which are also things that are valuable and worthy of protection. In the law of unjust enrichment, some of us have failed to articulate the causes of action. Th e majority of scholars in the fi eld, and some courts, have avoided this issue. I am here speaking principally of the approach pioneered by Peter Birks, an approach to which I have largely adhered. In my view, many scholars have avoided this issue unintentionally. Th ey have avoided it by simultaneously acting as if there is only one cause of action in unjust enrichment, while also acting as if there are multiple causes of action in unjust enrichment. Many textbooks on unjust enrichment contain a discussion as to whether unjust enrichment is itself a cause of action, or rather a ‘ principle ’ that might contain multiple causes of action. In general, this question is then dismissed as unimportant. 4 In my view, it is very important. In the next sections I will aim to explain why this is so. Before getting to that, it is important to say that diff erent scholars use the term ‘ unjust enrichment ’ in diff erent ways. Some include a great deal more in it than others. Some think it is only a principle; still others do not think it is useful at all. I will say something about this only because I think that the problem which I wish to highlight exists among all of those who treat unjust enrichment as a ground of liability. A. Big Unjust Enrichment Among those who write about unjust enrichment, even if we confi ne ourselves to those taking what might be called a Birksian approach, there is a somewhat 4 Smith, ‘ Defences ’ (n 1) 41. Restitution: A New Start? 89 hidden diversity of views as to what is the scope of this fi eld. Peter Birks himself had a very expansive view of its scope; indeed, one which grew during his career. 5 In his fi nal book, he included among claims in unjust enrichment, the following: (i) a claim by a person who had made a mistaken or compelled payment to recover it from the payee; (ii) a claim by a person to recover the value of benefi ts conferred under a contract that was later set aside or frustrated; (iii) a claim by a person who had paid taxes not due, without mistake, to recover them; (iv) a claim by a person who had discharged a debt, but who was not primar- ily liable, to recover from the person who was primarily or co-equally liable (including a claim by the fi rst person to take over rights of discharged credi- tors of the person primarily liable); (v) a claim by a person who had acted under necessity, against a person who had benefi ted from that act; (vi) a claim by a person for the benefi t acquired by another person from the use, without authority, of an asset in which the fi rst person held legal or equitable rights. In what follows I will call this ‘ big unjust enrichment ’ . In my view, one diffi culty about Birks ’ s project is this: he was unclear about causes of action. He frequently invoked the maxim that ‘ like cases must be treated alike ’ , as part of an argu- mentative strategy for the development of the law.6 But what is a ‘ like case ’ ? We do not assume that defences that are available to the tort of inducing breach of contract – such as ‘ justifi cation ’ – must be available to the tort of false impris- onment. Th ose are not ‘ like cases ’ , in the relevant sense, even though both are torts. Phrased in terms of causes of action, the problem is this: Birks, and others, have assumed or taken for granted that all examples of liability in the law of unjust enrichment fall under a single cause of action, and so must be treated alike in a strong sense: the elements of the claim must be the same, the defences must be the same, the things that are not relevant (such as the defendant ’ s ignorance of the conferral of a benefi t) must be the same. So far as I know, Birks never expressly 5 I examined how Birks ’ s view of unjust enrichment evolved over time precisely to include more and more claims within its scope, in L Smith , ‘ Tracing ’ in AS Burrows and A Rodger (eds), Mapping the Law: Essays in Memory of Peter Birks ( Oxford , Oxford University Press , 2006 ) 119 . He rejected any requirement that the plaintiff have transferred its rights to the defendant – indeed any requirement that the plaintiff have suff ered any loss at all – and he rejected any requirement that the plaintiff show a positive reason for restitution. 6 One prominent example was his conviction that since the common law provides strict liability for a mistaken payment, therefore a defendant should be strictly liable who receives trust property, even though in the latter case the claim only lies if the plaintiff ’ s interest survives: see, eg P Birks , ‘ Receipt’ in P Birks and A Pretto (eds), Breach of Trust ( Oxford , Hart Publishing , 2002 ) 213 . 90 Lionel Smith said that there is only one cause of action. But consciously or not, he took this for granted, because if there are multiple causes of action in unjust enrichment, as there are in the law of torts, then all these causes of action can be expected to reveal diversity in relation to all these aspects, just as is the case in the law of torts.