For many years, the very existence of a coherent Law of Restitution was a matter of debate. Thanks in no small measure to the work of academic writers such as Professors Birks and Jones, those doubts have now been banished: see, inter alia, the case of Lipkin Gorman v. Karpnale Ltd. [1991] 2 A.C. 548. Nevertheless, there remain within the subject a great many unanswered questions. In these two short books, the writers begin to look forward to their resolution.

In Restitution—The Future, Professor Birks is not principally concerned to answer substantive questions, but rather to clear the ground and set the agenda. The very great merit of the book is best appreciated if the reader keeps in mind the Preface to Professor Birks’ earlier work An Introduction to the Law of Restitution (1985, revised edn 1989; reviewed [1986] LMCLQ 540). There Professor Birks expresses his admiration for the merits of 19th century Austinian positivism with its distinction between the statement of the law and its evaluation and its passion for intellectual clarity, so that the book “does not often say what the law ‘ought’ to be. And when it does the appeal is to the humdrum values of intelligibility and consistency”. So, the agenda can be summarized as being the instilling into academic and practising lawyers alike the contours of and distinctions between the questions which must arise before a defendant can be said to have been unjustly enriched at the expense of the plaintiff so as to require him to make restitution.

Thus in Chapter 2, we are warned to distinguish between two different senses in which an enrichment may be at the expense of the plaintiff. The claim may, like the claim for a mistaken payment, be one in which the enrichment is at the plaintiff’s expense in that the defendant’s gain corresponds exactly to the plaintiff’s loss. Here the cause of action is unjust enrichment. Alternatively, the claim may be a claim for restitution of the profits of a breach of duty such as the tort of passing off. Here the cause of action is supplied by some other legal category. Restitution is merely a profits based remedy. This very real distinction should be contrasted with the false distinctions suggested by the differing labels such as “account of profits” and “waiver of tort”, which the courts have for historical reasons attached to profits based remedies. These false distinctions can only cloud what is the real question for the end of the 20th century, viz. which breaches of duty allow the victim to claim restitution as a remedy? Similarly, in Chapter 4 the writer argues that the distinction between money and nonmoney benefits is irrelevant when it comes to the question of whether an enrichment is unjust. Thus, facts sufficient to make an enrichment unjust and therefore to require restitution of enrichment in the form of money should equally lead to restitution of non-money enrichments. The only relevant distinction between money and non-money claims is in relation to the question of whether the defendant has in fact received a benefit. While the receipt of money will always be a benefit, it will often be difficult to show that work done by the plaintiff did enrich the defendant.

The case is powerfully argued and is largely convincing. Were the distinctions commended by Professor Birks more widely adopted disputes such as that which came before the Court of Appeal in Rover International Ltd. v. Canon Film Sales Ltd. [1989] 1 W.L.R. 912 would be resolved more quickly and in a way which gives clearer guidance to litigants and their advisers.

The case is made all the more powerful by two hugely impressive features of Professor