Baroness Carr of Walton-on-the-Hill, Lady Chief Justice of England and Wales, delivered a thought-provoking lecture at Queens’ College Cambridge on one of private law’s most contested questions: is there a unifying theory of unjust enrichment and restitution? Rocco Pirozzolo attended and reports on a talk that offered a fresh perspective on that question.
The Lady Chief Justice suggested that the long-running debate may be better approached in a different way. Rather than continuing a discussion that has so far proved inconclusive, she proposed a third path that offers a clearer and more useful way of understanding the subject.
What is unjust enrichment?
At its simplest, unjust enrichment is the legal principle that requires a person to restore a benefit received at another’s expense where there is no legal basis for them to retain it. A payment made by mistake or a sum paid under a contract that later falls through are familiar examples. In such cases, the law responds with restitution: the reversal of a benefit that ought not to have been kept.
The difficulty is that unjust enrichment covers a surprisingly wide range of situations, and no one has convincingly explained what single principle, if any, underlies the obligation to make restitution across all of them.
Starting with Wittgenstein
Baroness Carr opened with a striking image. In 1939, the Austrian philosopher Ludwig Wittgenstein gave a series of unscripted, two-hour lectures on the foundations of mathematics at King’s College, Cambridge. Among his audience was, in Baroness Carr’s words, “another of the great minds of the twentieth century”, Alan Turing. The two explored how the meaning of words depends on their use and context rather than on some fixed, hidden essence.
That insight, she argued, turns out to be exactly what the law of restitution needs.
The search for a grand theory
Restitution of unjust enrichment developed into a recognised area of English law following landmark cases such as Lipkin Gorman v Karpnale in 1991, though its roots stretch back centuries. Ever since, scholars have argued about whether there is a single principle that holds the whole subject together.
Baroness Carr surveyed the competing academic arguments, which range from those asserting that there is a single unifying theory that explains the whole subject to those arguing that restitution and unjust enrichment have no meaningful coherence at all and should not even be treated as unified areas of law.
A better way of thinking about it
Rather than choose between the search for a single unifying principle and the view that no such principle exists, the Lady Chief Justice proposed a third path, one grounded in Wittgenstein’s concept of family resemblance. Just as games share overlapping similarities without any single feature being common to all of them, the various claims that fall under the umbrella of restitution are related by a web of resemblances, not by a single defining essence.
This, she argued, is not a weakness in the subject. It reflects the way the common law typically develops, through analogy and incremental reasoning. In extending restitution by reference to earlier decisions, courts are doing exactly what Wittgenstein described: following shared rules whose meaning emerges from practice rather than abstraction.
The lecture set out the four questions that courts apply when considering whether unjust enrichment arises: Has the defendant been enriched? Was the enrichment at the claimant’s expense? Was the enrichment unjust? Are there any defences? These questions, the Lady Chief Justice suggested, are not a shortcut to a hidden essence; they are, as Lord Reed put it in a leading case on the subject, ‘signposts’, reflecting the Wittgensteinian approach Baroness Carr had outlined earlier in her lecture.
What this means for lawyers
The practical implication is significant. Rather than continuing to search for an overarching theory, the Lady Chief Justice called for rigorous conceptual clarification: sharpening our understanding of each of the four questions, mapping the family resemblance between different types of restitutionary claim and giving courts the clearest possible conceptual tools for deciding novel cases. The goal is not a grand unified theory but a clear and accurate account of the law as it actually operates.
Many thanks to Marius Nasta and Michael Zuckerman of Redress Solutions for the kind invitation to attend Baroness Carr’s compelling lecture, which was followed by a drinks reception and dinner in the Old Hall.
The full text of Baroness Carr’s lecture is available on the Judiciary website.
