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Lodder, Andrew, Enrichment in the Law of Unjust Enrichment and Restitution

Lodder, Andrew, Enrichment in the Law of Unjust Enrichment and Restitution
Table of Contents


enrichment challenges the prevailing orthodoxy in a fundamental way. It shows that enrichment is not a unitary element satisfied by a single test; rather, the same benefit may be understood in two different ways: (i) by the value of the benefit received (‘factual enrichment’); or (ii) by the change in the legal relations of the defendant effected by the acquisition of a right or the release of an obligation (‘legal enrichment’).

I. Unjust Enrichment

A. A Theoretical Framework

All legal rights are responses to causative events.6 These causative events can be divided into the categories of consent,7 wrongs,8 unjust enrichment9 and ‘other events’10 in what is often referred to as the ‘Birksian taxonomy’ of private law.


II. Restitution

This book takes the view that restitution is the reversal of the defendant’s enrichment. Restitution is a ‘gains-based’ response. It takes the form of a right or power to reverse the defendant’s enrichment at the claimant’s expense. Restitution is not restricted to giving that enrichment back to the claimant; it includes remedies that cancel or negate the enrichment received by the defendant.26

6J Austin, Lectures on Jurisprudence or the Philosophy of Positive Law, 5th edn (London, John Murray, 1885) 760; P Birks, ‘Equity in the Modern Common Law: An Exercise in Taxonomy’ (1996) 26 University of Western Australia Law Review 1; P Birks, Unjust Enrichment, 2nd edn (Oxford, Clarendon Press, 2005) 20.
7Eg contracts, declarations of trust, gifts, conveyances and wills.
8 Eg torts, equitable wrongs, breach of contract and breach of statutory duty.
9Enrichment at the expense of the claimant that is prima facie reversible due to the presence of an unjust factor: Pavey & Matthews v Paul (1987) 162 CLR 221 (HCA) 256–57 (Deane J); Portman BS v Hamlyn Taylor Neck [1998] 4 All ER 202 (CA) 206 (Millett LJ); Banque Financiere de la Cité v Parc (Battersea) Ltd [1999] 1 AC 221 (HL) 227 (Lord Steyn) 234 (Lord Hoffmann); Roxborough v Rothmans of Pall Mall Australia Ltd [2001] HCA 68, (2001) 208 CLR 516, 568 fn 257 (Kirby J); Rowe v Vale of White Horse DC [2003] EWHC 388 (Admin), [2003] 1 Lloyd’s Rep 418 [11] (Lightman J); Filby v Mortgage Express (No 2) Ltd [2004] EWCA Civ 759, [2004] 2 P&CR DG16 [62] (May LJ); P Birks, An Introduction to the Law of Restitution, revised edn (Oxford, Clarendon Press, 1989) 21; G Virgo, The Principles of the Law of Restitution, 2nd edn (Oxford, Oxford University Press, 2006) 9; A Burrows, The Law of Restitution, 3rd edn (Oxford, Oxford University Press, 2010) 26–27. See, eg Kelly v Solari (1841) 9 M&W 54, 152 ER 24.
10Eg finder’s rights, specification, accession and mixing.
26Cf Virgo, The Principles of the Law of Restitution (2006) (n 9) 4–5.

Referring Principles
Trans-Lex Principle: IX.1 - Basic rule
Trans-Lex Principle: IX.3 - Enrichment
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