Book Review: Fundamental Principles of Canadian Unjust Enrichment

Several times each month, we are pleased to republish a recent book review from the Canadian Law Library Review (CLLR). CLLR is the official journal of the Canadian Association of Law Libraries (CALL/ACBD), and its reviews cover both practice-oriented and academic publications related to the law.

Fundamental Principles of Canadian Unjust Enrichment. By Mitchell McInnes. Toronto: LexisNexis, 2025. xvii, 422 p. Includes table of cases, table of statutes, and index. ISBN 9780433527749 (softcover) $120.00.

Reviewed by Melanie R. Bueckert
Legal Research Counsel
Manitoba Court of Appeal

For readers unfamiliar with the topic of unjust enrichment, it stands alongside contract and tort as a primary source of private law obligations in Canada, although it is generally less well known than those other grounds of liability. This book is a pared-down, introductory version of McInnes’s comprehensive text The Canadian Law of Unjust Enrichment and Restitution, 2nd ed (Toronto: LexisNexis, 2022), which weighs in at 2,534 pages. This basic text aims to introduce the subject without getting too bogged down by the details. It includes a preface, a foreword (written by former Supreme Court Justice Russell Brown, who comments that McInnes’s larger treatise “may be the best textbook on any legal subject in Canada”), and a table of contents, as well as a table of cases, a table of statutes, and an index.

This text has four parts: Basic Principles, Absence of Juristic Reason, Defences, and Restitution. Basic Principles includes the key topics of enrichment, corresponding deprivation, and absence of juristic reason. The Absence of Juristic Reasons section discusses non-purposive transfers, donative intent, contract, disposition of law, as well as other juristic reasons. The Defences section addresses change of position, estoppel, passing on, illegality, officiousness, and incidental benefits. The concluding part, a chapter on restitution, discusses personal and proprietary restitution, including restitutionary trusts and equitable liens.

Interestingly, the book also includes approximately two dozen figures or diagrams: “[s]ome illustrate the subject’s organization and structure; others trace the operation of particular restitutionary doctrines” (p. vii). For example, the first figure (p. 7) breaks down the old writ of indebitatus assumpsit. Later figures illustrate specific types of transactions captured by the law of unjust enrichment, such as indirect enrichment (p. 63) or sub-contracts (p. 65). Perhaps most beneficial to those unfamiliar with the intricacies of unjust enrichment is a figure explaining the difference between unjust enrichment (backward-looking) and contract (forward-looking). As the accompanying text explains,

[t]he cause of action consists of a benefit that passed between the parties without legal explanation. There is no agreement, no promise, no wrongdoing. The court is simply presented with a transfer that should not have occurred. The only possible measure of relief is restitution. The transfer is reversed and nothing more. (p. 292)

In agreeing to prepare this review, I did not realize the controversy I was stepping into. It is apparent that the author of this text fundamentally disagrees with the approach taken by John McCamus, the other leading author in this area. In his foreword, Russell Brown observes that “The Canadian Law of Unjust Enrichment and Restitution is a comprehensive and uncharacteristically (in this subject area) agenda-free expounding of the doctrine of unjust enrichment and restitution” (p. ix). The primary point of disagreement appears to relate to the use of the terms “restitution” and “unjust enrichment” to describe the reversal of unjustified transfers between the parties and the stripping away of benefits obtained through civil wrongs (p. vi). In The Law of Restitution (Toronto: Thomson Reuters, 2004), Maddaugh and McCamus state,

[s]ome observers have taken the view, however, that the unjust enrichment principle does not simply provide an underlying justification for the existing liability rules and a basis for their reform and amendment, but that the principle in some sense replaces or supplants or suppresses the existing law of restitution. (§2:4)

In the corresponding footnote, the authors cite McInnes as the “principal proponent” of this view (§2:4).

McInnes, a professor at the University of Alberta, and McCamus, a professor at Osgoode, have both written lengthy treatises and shorter introductory texts in this area. Some law firms/organizations may already have access to The Law of Restitution through Westlaw. A quick search of CanLII indicates that 138 cases cite McInnes on the subject of unjust enrichment, with 47 of those cases arising in Alberta; meanwhile, 403 cases cite McCamus on the subject of restitution, including 137 in Ontario. Both have been cited multiple times by the Supreme Court of Canada.

I am not an expert in the area and so will not judge between the merits of these competing publications. Both are introductory texts, and both are similarly priced. McInnes’s text is newer. Students will be interested to note that a student edition of McInnes’s comprehensive text is available from LexisNexis at a significant discount ($210 versus $505), while McCamus’s loose-leaf is subject to the price uncertainty inherent in that publication format. Given the obvious differences of opinion between these two leading authors, it might be advisable for academic libraries to purchase both. Practitioners in the area may also wish to consult the work of both authors.