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UNJUST ENRICHMENT IN AUSTRALIA:
WHAT IS(N’ T) IT? IMPLICATIONS FOR LEGALREASONING AND PRACTICEKIT BARKER*
Much confusion currently attends the idea of unjust enrichment in Australian private
law. Although Australia was amongst the first Commonwealth common law jurisdictions
to recognise the idea, a more sceptical High Court in the latter part of the 20th century
and early years of the 21st century preferred to analyse restitutionary problems throughthe historical lens of the ancient forms of action and traditional equitable concepts ofgood conscience. This article articulates and distinguishes between five different roles thatunjust enrichment might play in modern legal reasoning in Australia, providing a clearer
picture of both what it is and — equally importantly — what it is not. A clearer view ofthe scope and function of the concept in legal reasoning will lead, it suggests, to a more
confident acceptance, and coherent use, of the idea of unjust enrichment by courts. It also
has key implications for the pleading of restitutionary claims.

CONTENTS
I Introduction ................................................................................................................... 1
II Unjust Enrichment: What Role Does It Play? ........................................................... 4
A Role 1: A Purely Moral Principle? .................................................................. 4
B Role 2: A ‘Unifying’ Legal Principle .............................................................. 7
C Role 3: A Legal Category ...............................................................................13
D Role 4: An Analytical Framework ................................................................20
E Role 5: A Cause of Action?............................................................................26
III Implications for the Pleading of Claims ..................................................................29
IV Conclusion ...................................................................................................................33

I INTRODUCTION
Much confusion currently exists in Australian law about the precise status of
the concept of unjust enrichment. There is an unfortunate historical irony in*Professor, TC Beirne School of Law, The University of Queensland. My thanks to theanonymous referees and to Lionel Smith for helpful comments. All errors remain my own.

Cite as:Kit Barker, ‘Unjust Enrichment in Australia: What Is(n’t) It? Implications for Legal Reasoning and Practice’(2020) 43(3) Melbourne University Law Review (advance)

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this. Pipped at the post only by radicals in Canada,1 Australia was, after all,amongst the first Commonwealth common law jurisdictions to vent the idea,
and indeed did so at the highest appellate level2 some four years before thisoccurred in England and Wales.3 Ordinarily, this advanced position on thefield of intellectual play would be a ground for celebration, not to say somelighthearted mockery of the Old Country’s historic conservatism andparticularised, insular ways of thinking. But something then happened, in thewake of the retirement of Justice Deane and Chief Justice Mason from theHigh Court Bench, that abruptly silenced the cheering crowd.4 At some stage
in the mid-to-late 1990s, the Court abruptly lost its enthusiasm for the ball,just as English courts really started to run with it. Influential members of the
new Court reverted to older, more familiar training patterns, preferring toanalyse restitutionary problems through the lens and language of the ancient
forms of action and traditional equitable concepts, rather than to accord theidea of unjust enrichment any very meaningful role in the law. Some members of the Bench went so far as to excoriate the idea as ‘top-down reasoning’or ‘dogma’,5 and as an unwelcome, academic import. Lower appellate courtsthat dared to use the idea creatively to change existing legal or (especially)equitable rules were publicly rebuked and instructed bluntly to desist.6 Unjust
enrichment was cast, for a time, as an invasive outsider, set on disrupting a1

Deglman v Guarantee Trust Co of Canada (Administrator of the Estate of Laura Constantineau
Brunet, deceased) [1954] SCR 725; Pettkus v Becker [1980] 2 SCR 834.

2

Pavey & Matthews Pty Ltd v Paul (1987) 162 CLR 221 (‘Pavey’).

3

Lipkin Gorman v Karpnale Ltd [1991] 2 AC 548 (‘Lipkin Gorman’). Commonwealth civilian
jurisdictions were onto the idea somewhat earlier, Scotland and Quebec having made theirown recognitions previously. On the history in Quebec, see generally Justice George Challies,
The Doctrine of Unjustified Enrichment in the Law of the Province of Quebec (Wilson &Lafleur, 2nd ed, 1952).

4

For a useful account of the various phases of the High Court’s engagement (and disengagement) with unjust enrichment reasoning from its early years to the current day, see EliseBant, ‘The Evolution of Unjust Enrichment and Restitution Law in the High Court of Australia’ (2017) 25 (Autumn) Restitution Law Review 121.

5

Roxborough v Rothmans of Pall Mall Australia Ltd (2001) 208 CLR 516, 544–5 [73], 545 [74](Gummow J) (‘Roxborough’), quoted in Farah Constructions Pty Ltd v Say-Dee Pty Ltd (2007)
230 CLR 89, 156 [151] (Gleeson CJ, Gummow, Callinan, Heydon and Crennan JJ) (‘Farah’).
See also Justice WMC Gummow, ‘Moses v Macferlan: 250 Years On’ (2010) 84(11) Australian
Law Journal 756, 757. Interestingly, in Bofinger v Kingsway Group Ltd (2009) 239 CLR 269(‘Bofinger’), Gummow, Hayne, Heydon, Kiefel and Bell JJ described top-down reasoning as afeature of ‘some all-embracing’ theories of unjust enrichment, rather than of all such theories:
at 300 [90] (emphasis added).

6

Farah (n 5) 148–59 [130]–[158] (Gleeson CJ, Gummow, Callinan, Heydon and Crennan JJ).

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3house that was already very much in order and that could happily live without
its interfering tendencies.
It is only in recent times, with further changes in the composition of theHigh Court, that there are signs of a new, cautious acceptance. The development in Australian law of a defence of change of position in AustralianFinancial Services and Leasing Pty Ltd v Hills Industries Ltd (‘Hills’)7 has now
made this re-engagement with unjust enrichment thinking inevitable. Indeed,
despite an unfortunate and often misunderstood paragraph in the plurality
judgment in Hills (to which we shall return), this case will almost certainly
prove to be Australia’s Lipkin Gorman v Karpnale Ltd (‘Lipkin Gorman’)8 — alittle late in coming, perhaps, but here at last. In the meantime, the American
Law Institute has completed its third restatement of the law, in the processelevating the concept of unjust enrichment to the title page of the work,9 andthe High Court has referenced that work several times (albeit in a different
context) in the recent decision of Thorne v Kennedy.10 One (new) member ofthe current High Court Bench, Justice Edelman, is co-author of an important
text, now in its second edition, that also bears the concept boldly upon its
cover,11 and his Honour’s influence can already be seen, I suggest, in theplurality judgment of the High Court in the most recent case of Mann v
Paterson Constructions Pty Ltd (‘Mann’).12 Whilst the next 10 years will be
critical in determining Australia’s attitude to the unjust enrichment game,
there are therefore good reasons to think that the ball that was dropped by theHigh Court in the early years of the new millennium may yet be retrieved
from the mud.
7(2014) 253 CLR 560 (‘Hills’).

8

Lipkin Gorman (n 3).

9American Law Institute, Restatement (Third) of Restitution and Unjust Enrichment (2011) § 1(‘Third Restatement’). Interestingly, the term was originally to feature in even the first restatement, but was dropped, at the publisher’s instigation, because of its unfamiliarity
amongst practitioners: Andrew Kull, ‘Restitution and Unjust Enrichment’ in Elise Bant, Kit
Barker and Simone Degeling (eds), Research Handbook on Unjust Enrichment and Restitution(Edward Elgar, 2020) 62, 69–70.

10(2017) 263 CLR 85, 99 [30] n 48, 100 [32] n 57 (Kiefel CJ, Bell, Gageler, Keane andEdelman JJ).

11

Justice James Edelman and Elise Bant, Unjust Enrichment (Hart Publishing, 2nd ed, 2016).
The elevation of the concept to the title page is now a clear trend: see, eg, Peter Birks, Unjust
Enrichment (Oxford University Press, 2nd ed, 2005); Robert Goff and Gareth Jones, The Lawof Unjust Enrichment, ed Charles Mitchell, Paul Mitchell and Stephen Watterson (Sweet &Maxwell, 9th ed, 2016); Kit Barker and Ross Grantham, Unjust Enrichment (LexisNexis Butterworths, 2nd ed, 2016).

12(2019) 373 ALR 1, 29–63 [109]–[217] (Nettle, Gordon and Edelman JJ) (‘Mann’).

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Australia is not the only country to have suffered crises of confidence overthe idea of unjust enrichment. There are scholars elsewhere who continue toharbour old doubts and even to express new ones.13 The purpose of this pieceis to identify the role that the idea currently plays in Australian law in the
post-Hills era, and to suggest how it can fruitfully be understood and accommodated within the developing jurisprudence of this country. Many of thereservations about the idea that have troubled the High Court in recent times,
I shall argue, stem from a failure to distinguish clearly between five distinct
roles that the idea might play in legal reasoning, as well as from the Court’s
justified anxiety about two of these roles in particular. A clearer view of what
unjust enrichment is and, equally importantly, what it is not can lead, Isuggest, to its more confident acceptance and coherent use by Australian
courts. It will also assist practitioners in determining how properly to plead
modern restitutionary claims.
I I U N J U S T E N R I C H M E N T : W HAT R O L E D O E S I T P L AY ?
A Role 1: A Purely Moral Principle?
The first role that the idea might play, which has been clearly rejected by theHigh Court, the American Restatement (Third) of Restitution and Unjust
Enrichment (‘Third Restatement’), and all other courts to date, is as a purely
moral principle, external to the law and lying recumbent in the conscience ofa judge. The seeds of a moral principle are certainly ancient and can be foundin Pomponius’s well-known maxim: ‘It is by nature fair that no one should
gain through another’s loss’.14 Even as a moral proposition, this idea neededsome work, for it is by no means obvious that the mere fact of gaining byanother’s loss identifies anything that is ‘by its nature’ unfair. In any market
economy, the fact that one’s own profit corresponds to a loss another has
13

For the latest wave of scepticism (of a sort), see, eg, Lionel Smith, ‘Restitution: A New Start?’
in Peter Devonshire and Rohan Havelock (eds), The Impact of Equity and Restitution in
Commerce (Hart Publishing, 2019) 91; Robert Stevens, ‘The Unjust Enrichment Disaster’(2018) 134 (October) Law Quarterly Review 574.

14

The Digest of Justinian, ed Alan Watson tr Alan Watson (University of Pennsylvania Press,
1985) vol 1, 380, [12.6.14] (Nem hoc natura aequum est, neminem cum alterius detrimento
fieri locupletiorem). In the cited secondary source, the English translation appears as: ‘For it isby nature fair that nobody should enrich himself at the expense of another’. This is colloquially easier than the translation provided in the text, but it does not highlight the key meaningof the word ‘detrimentum’ (loss, damage) that is the central focus of the point being made —namely, that a loss on the part of A is insufficient, without more, to give rise to any moral
responsibility on the part of B for a resulting gain.

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suffered is surely regarded as (at worst) ethically neutral in the absence ofsome identifiable error, exploitation, or wrongdoing. For any moral ‘unfairness’ to be present in a transaction, the winner’s gain, correlating to the loser’s
loss, must hence be attended by additional circumstances making it unjust.15
Pomponius’ principle must therefore be understood as a principle against‘gaining unjustly through another’s loss’, not simply ‘gaining from loss’. Indeed
there are points in the Digest which suggest as much.16 Even when thisadjustment is made, however, it is clear that, for legal purposes, the definitionof injustice in this formulation cannot lie outside of the law itself in the
personal conscience of a judge, or even in his or her perception of the moral
consensus of the community. Courts and commentators are unanimous on
this point, emphasising that any principle against unjust enrichment existingin the modern law is a legal principle derived from decided cases and concrete
legal norms.17 It works from the legal ground up, not from the moral heavens
down.
The point was made right from the outset by Deane J in Pavey & Matthews
Pty Ltd v Paul (‘Pavey’)18 in 1987, where his Honour emphasised that identifying a law of restitution unified by a principle of unjust enrichment is ‘not toassert a judicial discretion to do whatever idiosyncratic notions of what is fairand just might dictate’.19 The passage was cited by the High Court in David
Securities Pty Ltd v Commonwealth Bank of Australia (‘David Securities’)20 in
1992, where the majority added:

15

For a plaintiff to be morally responsible to another for a gain, there must be not just a causal
correlation between the two, but an infringement of an entitlement of the plaintiff — some‘harm’ to the plaintiff: Kit Barker, ‘The Nature of Responsibility for Gain: Gain, Harm, andKeeping the Lid on Pandora’s Box’ in Robert Chambers, Charles Mitchell and James
Penner (eds), Philosophical Foundations of the Law of Unjust Enrichment (Oxford University
Press, 2009) 150, 152–8.

16

The additional element appears in an alternative formulation of the maxim: ‘By the law ofnature it is fair that no one become richer by the loss and injury of another’ (Iure naturae
aequum est neminem cum alterius detrimento et iniuria fieri locupletiorem): Watson (n 14)
vol 4, 483, [50.17.206]. The additional concept of injuria in this version emphasises not
simply loss, but wrongful loss. See also Alan Rodger, ‘What Did Damnum Iniuria Actually
Mean?’ in Andrew Burrows and Lord Rodger (eds), Mapping the Law: Essays in Memory ofPeter Birks (Oxford University Press, 2006) 421.

17

For commentators, see, eg, Peter Birks, An Introduction to the Law of Restitution (Clarendon
Press, 1985) 19 (‘Introduction’); Goff and Jones (n 11) 7–8; Edelman and Bant (n 11) 12–13.

18

Pavey (n 2).

19

Ibid 256.

20(1992) 175 CLR 353 (‘David Securities’).

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Melbourne University Law Review[Vol 43(3):Adv[I]t is not legitimate to determine whether an enrichment is unjust by reference
to some subjective evaluation of what is fair or unconscionable. Instead, recovery depends upon the existence of a qualifying or vitiating factor such as mistake, duress or illegality.21

More recently, in the Hills case, Gageler J observed, consistently with this lineof thinking, that the notion of injustice lying at the heart of the principle
against unjust enrichment is ‘descriptive, accumulative and incremental’.22 His
Honour cited the following passage from the first instance judgment ofCampbell J in Wasada Pty Ltd v State Rail Authority of New South Wales[No 2] (‘Wasada’),23 which neatly summarises both the objection to the ideaof unjust enrichment as a purely moral idea and the conclusive answer to that
objection:‘Unjust’ is the ‘generalisation of all the factors which the law recognises as calling for restitution’. Because we need to search for recognised factors, examination of which involves an analysis of case law, the reference to ‘injustice’ as anelement of unjust enrichment, is not a reference to judicial discretion. Normal
judicial processes are involved and it is only in cases where there is no recognised basis for saying that injustice has arisen that problems can arise.24

Statements to similar effect appear in the jurisprudence of the House ofLords,25 the United Kingdom Supreme Court,26 and the Third Restatement.27
They ought straightforwardly to eliminate any misconception that unjust
enrichment plays a loose moral role, tends to subjectivity, or derives its
meaning in isolation from existing rules of law.

21

Ibid 379 (Mason CJ, Deane, Toohey, Gaudron and McHugh JJ).

22

Hills (n 7) 619 [141]. See also at 579 [20] (French CJ).

23

[2003] NSWSC 987 (‘Wasada’).

24

Ibid [16], quoted in Hills (n 7) 619 [141] (emphasis added) (citations omitted). This passage,
which itself quotes Keith Mason and JW Carter, Restitution Law in Australia (Butterworths,
1995) 59–60 [227], was cited with approval in Barnes v Eastenders Cash & Carry plc [2015]
AC 1, 41 [102] (Lord Toulson JSC for the Court) (‘Eastenders’).

25

See, eg, Lipkin Gorman (n 3) 578 (Lord Goff).

26

Investment Trust Companies v Revenue and Customs Commissioners [2018] AC 275, 294 [39](Lord Reed JSC for the Court) (‘Investment Trust’).

27

Third Restatement (n 9) § 1 cmt (b).

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B Role 2: A ‘Unifying’ Legal Principle
If the proscription against unjust enrichment is a principle, it is therefore alegal principle, not a moral one. Legal principles can (and hopefully do) ofcourse have moral content and merit, but the point is that their morality isembedded in existing rules and precedents and is therefore objectively
determined. It does not spring in a Panglossian rush from hope itself. Legal
principles may be understood as differing from legal rules in the detail thatthey operate at a higher level, expressing in a more general way the reason(s)underpinning those rules and precedents.28 They are not usually used in thelaw in a dispositive manner29 — that is, to determine cases, or to dictate
results by themselves, without reference to lower-order rules. This is because
their generality makes them hard to apply predictably to naked sets of facts
and leaves too much to a court’s discretion. Both of these features make legal
principles potentially problematic from a rule of law point of view. However,by referring judges to the broader values and aims that underpin existing
rules, they can assist in interpreting and applying those rules and in deciding
new cases. In this regard, principles have an important developmental role toplay. The reasons behind rules — referenced through the principles thatextrapolate from them — are capable of extending their normative logic
beyond the limits of the rules themselves, thereby casting light upon the pathahead. In so far as legal principles play only this broad, guiding role and are
insufficient in themselves to ‘ground’ legal claims in private law, they are to beclearly distinguished from ‘causes of action’, or legal ‘bases of decision’. Theiruse is entirely consistent with a cautious, incremental approach to thedevelopment of the law.
The idea that the proscription against unjust enrichment is a high-level,
unifying legal principle in the defined sense was endorsed by Deane J(Mason J agreeing) in the early case of Muschinksi v Dodds (‘Muschinski’),30
28

The distinction between legal rules and principles is sometimes expressed by writers in
different ways, and the value of the distinction itself is sometimes contested. For the senses inwhich the proscription against unjust enrichment can usefully be understood as a principle,
not a rule, see Kit Barker, ‘Understanding the Unjust Enrichment Principle in Private Law: A
Study of the Concept and Its Reasons’ in Jason W Neyers, Mitchell McInnes and Stephen GA
Pitel (eds), Understanding Unjust Enrichment (Hart Publishing, 2004) 79, 90–2 (‘Understanding the Unjust Enrichment Principle’).

29

In the common law tradition at least. Matters are somewhat different in codified, civilian
traditions and there is some evidence that the principle has, on occasion, been used in thisway in Canada: see MM Litman, ‘The Emergence of Unjust Enrichment as a Cause of Action
and the Remedy of Constructive Trust’ (1988) 26(3) Alberta Law Review 407.

30

(1985) 160 CLR 583 (‘Muschinski’).

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where his Honour described the idea as a ‘notion underlying a variety of
distinct categories of case in which the law has recognized an obligation on
the part of a defendant to account for a benefit derived at the expense of aplaintiff ’.31 In Pavey, his Honour expanded upon the analysis in a now muchcited passage, opining that unjust enrichment isa unifying legal concept which explains why the law recognizes, in a variety of
distinct categories of case, an obligation on the part of a defendant to make fairand just restitution for a benefit derived at the expense of a plaintiff and whichassists in the determination, by the ordinary processes of legal reasoning, of thequestion whether the law should, in justice, recognize such an obligation in a
new or developing category of case.32

The clear suggestion in this excerpt that unjust enrichment is a ‘legal’ idea,that can ‘explain why’ the law contains various rules requiring restitution to be
made, that it helps decide whether there ‘should’ be such duties, and that it
has a role in helping judges to apply and ‘develop’ these rules in new cases, sits
comfortably with the proposition that it is an explanatory legal principle withnormative weight.33 His Honour’s words have been cited on numerous
occasions in the High Court,34 so that the developmental function of theprinciple must now be taken to have been endorsed. In Bofinger v Kingsway
Group Ltd (‘Bofinger’),35 even Gummow, Hayne, Heydon, Kiefel and Bell JJ (adecidedly sceptical bench) hence accepted that the idea can be used constructively to ‘compar[e] and contras[t] various categories of liability’36 and to‘assist in the … recognition of obligations in a new or developing category ofcase’.37 The Court has also said on several occasions, in the context of unjust
31

Ibid 617.

32

Pavey (n 2) 256–7.

33

See also David Securities (n 20) 406, in which Dawson J noted that ‘unjust enrichment does
not of itself constitute a cause of action, [but] provides a “unifying legal concept”’. Birks
appears originally to have denied the principle any normative status: Birks, Introduction(n 17) 23–4. However, he later revised that view, describing the principle as ‘weakly normative’ in ‘gather[ing] up’ the law’s ‘reasons’: Birks, Unjust Enrichment (n 11) 274.

34

See, eg, Lumbers v W Cook Builders Pty Ltd (in liq) (2008) 232 CLR 635, 665 [85] (Gummow,
Hayne, Crennan and Kiefel JJ) (‘Lumbers’); Equuscorp Pty Ltd v Haxton (2012) 246 CLR 498,
515 [29] (French CJ, Crennan and Kiefel JJ) (‘Equuscorp’); Hills (n 7) 615 [130] (Gageler J);
Mann (n 12) 21 [74] (Gageler J), 56 [199] (Nettle, Gordon and Edelman JJ).

35

Bofinger (n 5).

36

Ibid 299 [88].

37

Ibid 300 [89]. See also Friend v Brooker (2009) 239 CLR 129, 141 [7] (French CJ, Gummow,
Hayne and Bell JJ) (‘Friend’); Lumbers (n 34) 665 [85] (Gummow, Hayne, Crennan andKiefel JJ); Hills (n 7) 618 [139] (Gageler J).

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9enrichment, that ‘the emergence of a general principle [is not] precluded
when derived from judicial decisions upon particular instances’.38 This isimportant, because it shows that there is nothing objectionable, in the Court’sview, about a principle against unjust enrichment, provided that it does notoperate a priori and in pure abstraction, but rather as an interpretive device inunderstanding and developing existing restitutionary rules. In Mann, this useof the principle as a device for incrementally developing existing restitutionary rules was expressly approved by the plurality.39
An example of the principle’s utility as a developmental tool that has recently been provided by the High Court itself is the recognition that payments
made by mistake of law should be recoverable in exactly the same way — andfor the same underlying reasons — as those made by mistake of fact.40
Another is the recognition in Mann and other cases that a failure of consideration provides a ground for restitution in cases involving the supply ofservices, as much as it does in cases involving money or property.41 Other
examples — not yet fully accepted in Australia, but acknowledged
elsewhere — are the recognition that some (not all) cases involving equitable
remedies such as subrogation,42 equitable contribution, indemnity and the38

Equuscorp (n 34) 516–17 [30] (French CJ, Crennan and Kiefel JJ), citing Farah (n 5)
158 [154] (Gleeson CJ, Gummow, Callinan, Heydon and Crennan JJ). See also Roxborough(n 5) 544 [72] (Gummow J); Friend (n 37) 141 [7] (French CJ, Gummow, Hayne and Bell JJ):
‘the concept of unjust enrichment … may assist, by the ordinary processes of legal reasoning,in the development of legal principle’.

39

Mann (n 12) 61–2 [213] (Nettle, Gordon and Edelman JJ).

40

Bofinger (n 5) 300 [89] (Gummow, Hayne, Heydon, Kiefel and Bell JJ), discussing David
Securities (n 20). Another potential example of its developmental function is Winterton
Constructions Pty Ltd v Hambros Australia Ltd (1991) 101 ALR 363, 373–6 (Federal Court)(‘Winterton’), where Gummow J refused to strike out a novel claim for unjust enrichment, inthe light of the field’s rapid development, even though the claim in that case seems now tohave been almost certain to fail.

41

Mann (n 12) 22 [78] (Gageler J), 45 [168]–[169] (Nettle, Gordon and Edelman JJ); Cobbe v
Yeoman’s Rowe Management Ltd [2008] 1 WLR 1752, 1756 [3], 1774 [43] (Lord Scott, Lord
Hoffmann agreeing at 1754 [1], Lord Brown agreeing at 1789 [94], Lord Mance agreeing
at 1789 [95]) (House of Lords); Benedetti v Sawiris [2014] AC 938, 982 [98] (Lord Reed JSC)(‘Benedetti’); Eastenders (n 24) 1297–9 [108]–[116] (Lord Toulson JSC, Baroness Hale DPSC
and Lords Kerr, Wilson and Hughes JJSC agreeing). In Australia, see Lampson (Australia)
Pty Ltd v Fortescue Metals Group Ltd [No 3] [2014] WASC 162, [92]–[94] (Edelman J)(‘Lampson’).

42

See, eg, Banque Financière de la Cité v Parc (Battersea) Ltd [1999] 1 AC 221, 231–7(Lord Hoffmann, Lord Griffiths agreeing at 228) (‘Banque Financière’); Menelaou v Bank ofCyprus UK Ltd [2016] AC 176 (‘Menelaou’); Swynson Ltd v Lowick Rose llp (in liq) [2018] AC
313, 325 [19] (Lord Sumption JSC, Lord Neuberger PSC and Lords Clarke and Hodge JJSC
agreeing) (‘Swynson’).

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constructive (or resulting) trust43 proceed according to the same normative
logic as cases in which parties have benefitted others through the payment ofmoney by mistake, under compulsion, on a basis that has failed, or where they
have had money or other assets taken from them without their knowledge
and consent.
A further, famous, but unsuccessful, attempt was made by the New South
Wales Court of Appeal in Say-Dee Pty Ltd v Farah Constructions Pty Ltd(‘Farah (Court of Appeal)’)44 to use the unjust enrichment principle to informthe development of the law of knowing receipt, so as to liberalise existing
liability principles and bring them into line with standards of liability andlogics applying in unjust enrichment claims at common law. On this occasion,
the High Court held this to be a mistake.45 Since then, however, the principle
has ironically been used by lower courts to develop a separate range of strict,personal liabilities both at law and in equity outside the knowing receipt
category, which achieve similar, liberalising effects in cases involving misdirected assets — at least in cases in which recipients of those assets still possessthem at the time of trial.46 These developments have not been regarded bylower courts as inconsistent with the continuation of fault liability under the
first limb of Barnes v Addy,47 even though they diminish its practical importance in certain instances and incrementally change the legal landscape forthe benefit of victims of fraud. Although they do not formally contradict thelaw of knowing receipt, they therefore nevertheless coalesce toward theacceptance of a greater range of strict liabilities that calls traditional faultbased assumptions into question. The logic of the posited strict liabilities lies
in claims at common law that are based on a defendant’s unjust enrichment.
43

See, eg, Muschinski (n 30); Black v S Freedman & Co (1910) 12 CLR 105; Wambo Coal
Pty Ltd v Ariff (2007) 63 ACSR 429 (Supreme Court of New South Wales) (‘Wambo’). See
also James Edelman, ‘Unjust Enrichment and the Law of Trusts’ (2011) 35(3) Australian Bar
Review 219; Edelman and Bant (n 11) 38–42.

44[2005] NSWCA 309, [218]–[221] (Tobias JA for the Court) (‘Farah (Court of Appeal)’). For
another unsuccessful attempt, this time to use unjust enrichment to extend the doctrine ofequitable contribution to cases involving common designs, see Friend (n 37) 154–5 [63]–[66](French CJ, Gummow, Hayne and Bell JJ).

45

Farah (n 5) 148–59 [130]–[158] (Gleeson CJ, Gummow, Callinan, Heydon and Crennan JJ).

46

See, eg, Fistar v Riverwood Legion and Community Club Ltd (2016) 91 NSWLR 732,
742–3 [45]–[47] (Leeming JA, Bathurst CJ agreeing at 734 [1], Sackville AJA agreeingat 750 [88]); Great Investments Ltd v Warner (2016) 243 FCR 516, 530 [54]–[55] (Jagot,
Edelman and Moshinsky JJ). See also Elise Bant and Michael Bryan, ‘Outflanking Barnes v
Addy? The Persistence of Strict Recipient Liability’ (2017) 11(3) Journal of Equity 271,
273–80.

47(1874) LR 9 Ch App 244.

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The availability to innocent recipients of the new defence of change of
position makes such strict personal liabilities more morally acceptable in themodern day than they were in the past.
Whilst there is still disagreement, therefore, about the precise categories ofcase which instantiate the idea of unjust enrichment (a matter we address
further below), there is now little dissent, I suggest, from the view that it
functions as a ‘unifying legal principle’ in those cases in which it is genuinely
in point.48 The idea that the principle is ‘unifying’ should not be taken tosuggest that there is only one (and the same) reason for restitution in every
instance.49 The idea is simply that cases of unjust enrichment share certain
normative features implicit in the idea of one person gaining unjustly at theexpense of another. The precise reason why the gain is unjust may differ as
between different types of case. It will also be evident from this conceptionthat the degree of guidance which the principle is capable of providing in newcases is weak, if one attempts to apply it in abstracto. Indeed, in its wholly
abstracted format, the principle is as inchoate as the vague idea, instantiatedin the law of torts, that one should not unjustly cause another person loss.
What could this possibly mean in practice? How could one use the principle
precisely? The principle against unjust enrichment only usefully assists a judge
in making choices in a fresh, concrete instance when it is used to refer thejudge back to the reasons underpinning the individual rules and cases fromwhich it abstracts. It is this capacity of the idea to connect courts to common
reasons appearing in a wide range of particularised cases that makes it usefulas a guide in developing the law incrementally in new instances.50
Assuming that the proscription against unjust enrichment is genuinely alegal principle, how, then, is it best expressed? Currently, its form differs
slightly between jurisdictions. At least since the High Court’s decision in

48

This proposition appears to be strongly rejected by Ian Jackman, who suggests that the High
Court of Australia has ‘repeatedly refused to adopt the supposed over-arching principle of“unjust enrichment at the plaintiff ’s expense” and that it is “not feasible to force uniformity
on [the cases] in terms of the so-called unifying principle”’: Ian Jackman, The Varieties ofRestitution (Federation Press, 2nd ed, 2017) vii, 1. These assertions seem to be based on adifferent understanding of what constitutes a ‘unifying principle’ to that adopted here, or by
the cases cited in this part. The main thesis of Jackman’s book is that the field contains a wide
variety of different classes of case and that there is no single reason for restitution (I would
say no single cause of action) — propositions which this article endorses.

49

See Barker, ‘Understanding the Unjust Enrichment Principle’ (n 28) 95.

50

Ibid 92–5. See also Kit Barker, ‘Theorising Unjust Enrichment: Being Realist(ic)? (2006)
26(3) Oxford Journal of Legal Studies 609, 615–16.

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Roxborough v Rothmans of Pall Mall Australia Ltd (‘Roxborough’),51 it hashence been customary for Australian courts to state the principle as one
according to which a person must make restitution of benefits which it wouldbe ‘against conscience’ or ‘unconscionable’ for him or her to retain,52 muchbeing made of the ‘equitable’ historical foundations of even the common law
action for money had and received in Moses v Macferlan (‘Moses’).53 This
statement provides two contrasts with the way in which the principle is statedin England and Wales, neither of which turns out to be of consequence, once
it is unpicked.
The first lies in the fact that English courts generally express the principle
in terms of the ‘injustice’ of benefitting at another’s expense, not its ‘unconscionability’ or ‘unconscientiousness’.54 This is a distinction without a practicaldifference. As the High Court recognised in Australia and New Zealand
Banking Group Ltd v Westpac Banking Corporation (‘Westpac’),55 Equuscorp
Pty Ltd v Haxton56 and Hills, ‘legal principles of restitution or unjust enrichment can be equated with seminal equitable notions of good conscience’,57
which is to say that there is no difference in substance between liability forunjust benefits and unconscionable or unconscientious ones. ‘Unjust enrichment’ is the modern terminology for enrichment that has historically been
regarded as ‘against conscience’.58
51

Roxborough (n 5).

52

Ibid 543 [71], 555 [100] (Gummow J). See also Perpetual Trustees Australia Ltd v Heperu Ltd
Pty Ltd (2009) 76 NSWLR 195, 221 [128] (Allsop P and Handley AJA) (‘Perpetual Trustees’);Hills (n 7) 592–3 [65]–[66] (Hayne, Crennan, Kiefel, Bell and Keane JJ).

53

(1760) 2 Burr 1005; 97 ER 676, 678–9 (Lord Mansfield for the Court) (‘Moses’).

54

See, eg, Benedetti (n 41) 982 [99] (Lord Reed JSC); Investment Trust (n 26) 294 [39] (LordReed JSC for the Court).

55(1988) 164 CLR 662 (‘Westpac’).

56

Equuscorp (n 34).

57

Westpac (n 55) 673 (Mason CJ, Wilson, Deane, Toohey and Gaudron JJ), quoted in
Equuscorp (n 34) 517 [32] (French CJ, Crennan and Kiefel JJ), Hills (n 7) 576 [16](French CJ), 595 [74] (Hayne, Crennan, Kiefel, Bell and Keane JJ).

58

Baltic Shipping Co v Dillon (1993) 176 CLR 344, 359 (Mason CJ) (‘Baltic Shipping’). See also
W Cook Builders Pty Ltd (in liq) v Lumbers (2007) 96 SASR 406 (‘Lumbers (Full Supreme
Court)’), where the plurality noted that the ‘injustice’ of a plaintiff not being remunerated forwork can also be expressed as ‘unconscionable’ retention of a benefit by the defendant:
at 420 [63] (Sulan and Layton JJ); Hills (n 7) 618 [138] (Gageler J). Note that this is not to saythat the concepts of unjust enrichment and unconscionability are fully coterminous, because
the latter concept has clearly been used as the foundation of liability in a host of situations
not involving liability for benefits obtained. This is the point made by Gummow J in Roxborough (n 5) 543–4 [71]. The point being made in the text is that where liability has historically been imposed on a defendant for a benefit obtained at the expense of a plaintiff, it

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The second contrast lies in the fact that the Australian formulation of theprinciple emphasises the unconscionability of a defendant retaining anenrichment at the plaintiff ’s expense, as opposed to the injustice of him or her
first receiving it.59 This is potentially a genuine difference, but is best understood as a historical anomaly arising from the fact that, until very recently,
Australian law lacked any (explicit) change of position defence.60 This may
have led courts to concern themselves, when formulating the basic liability
principle, with ensuring that defendants who had innocently dissipated abenefit (and who therefore no longer still ‘retained’ it) had no liability torestore its value. The subsequent development of the change of position
defence in Hills means that concerns about the unfairness of requiring an
innocent to repay value he or she no longer retains can now be accommodated at the defence stage. Indeed, in Southage Pty Ltd v Vescovi (‘Vescovi’)61 —decided a year or so after Hills — the Victorian Court of Appeal took an
important step in this direction, suggesting that the question whether it isunconscionable for a defendant to ‘retain’ a benefit is now relevant only torestitutionary defences, not to the basic liability principle.62 That interpretation is consistent with Hills and with the approach of the High Court itself inDavid Securities.63 If it is followed, as I propose it should be, then the second
distinction between Australian and English formulations of the principle
against unjust enrichment will turn out to be as illusory as the first.
C Role 3: A Legal Category
A third role for the idea, which has also recently been embraced by somemembers of the High Court, is a taxonomic one. Unjust enrichment in thisconstruction describes a defined and distinct body of private law, alongsidecontract and tort,64 which collects for interpretive and organisational purposes those legal events in consequence of which one person has gained unjustly
makes no difference whether this is expressed in terms of liability for ‘unjust’ or ‘unconscionable’ enrichment.
59

See, eg, Roxborough (n 5) 548 [83] (Gummow J); Perpetual Trustees (n 52) 221 [128](Allsop P and Handley AJA); Hills (n 7) 592–3 [65]–[67] (Hayne, Crennan, Kiefel, Bell and
Keane JJ).

60

See generally Elise Bant, The Change of Position Defence (Hart Publishing, 2009) 1.

61(2015) 321 ALR 383 (‘Vescovi’).

62

Ibid 395 [48]–[50] (Warren CJ, Santamaria JA and Ginnane AJA).

63

David Securities (n 20) 379 (Mason CJ, Deane, Toohey, Gaudron and McHugh JJ).

64

See Banque Financière (n 42) 227 (Lord Steyn), cited in Investment Trust (n 26) 294 [39](Lord Reed JSC for the Court).

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Melbourne University Law Review[Vol 43(3):Advat another’s expense and may be required to relinquish that gain to the other.
In Equuscorp, French CJ, Crennan and Kiefel JJ hence indicated that[u]njust enrichment … has a taxonomical function referring to categories ofcases in which the law allows recovery by one person of a benefit retained byanother. … [I]t does not found or reflect any ‘all-embracing theory of restitutionary rights and remedies’.65

Recent references to the taxonomic function of the idea also appear in the
judgments of French CJ and Gageler J in Hills,66 and in the first instancejudgment of Edelman J in Lampson (Australia) Pty Ltd v Fortescue Metals
Group Ltd [No 3] (‘Lampson’),67 where his Honour suggested that the ‘category … assists in understanding’ and ‘directs attention to a common legal
foundation shared by a number of instances of liability formerly concealed
within the forms of action or within bills in equity’.68 They also appear in theplurality judgment in Mann, to which his Honour contributed.69
These statements accept that unjust enrichment law is indeed a legal category. They also suggest that it has further subcategories, that it is capable ofexpanding incrementally, that it contains rules originating both at common
law and in equity, and that — although it collects cases that have importantfeatures in common — it is not an ‘all-embracing theory’. This last statement isambiguous, but I take it to mean that the scope of the category is limited anddoes not encompass or explain (‘theorise’) everything. Given that it is a logicalimpossibility for an interpretive category to contain or explain more than thatwhich it encompasses, the intention of this statement must be to reflect theHigh Court’s view that academics and judges have sometimes gone too far inseeking to rationalise particular rules and doctrines as lying within thedomain of unjust enrichment law.
The precise scope of the category lies beyond the reach of this piece. Here I
identify just two main points of controversy.70 One — which troubles academ-

65

Equuscorp (n 34) 516 [30], quoting Roxborough (n 5) 544 [72] (Gummow J).

66

Hills (n 7) 579 [20] (French CJ), 618 [138]–[139] (Gageler J).

67

Lampson (n 41).

68

Ibid 17 [51].

69

Mann (n 12) 39 [150], 42–3 [162], 56 [199] (Nettle, Gordon and Edelman JJ).

70

Two others concern: (i) whether cases in which a plaintiff traces his or her property througha variety of substitutes (losing title to the original property in the process) are to be classified
as lying in property law, or unjust enrichment law; and (ii) in which cases (if any) a claim for‘user fee’ damages or for a reasonable license fee are claims for compensation for loss, or
restitution of a negative gain made by a defendant. Both topics are too large to broach here.

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ics more than it currently does courts — is whether it comprises all cases inwhich defendants have gained at another’s expense (including cases in which
they have done so by a recognised wrong, such as a tort), or only cases inwhich there has been a gain without such a wrong — typically by virtue of atransfer of resources between the parties which is subject to a volitional
defect. The Third Restatement places all such cases within the category of
unjust enrichment, whilst recognising that they are still different in important
respects,71 whereas most modern English and Australian authors (including
Justice Edelman writing extracurially with Professor Bant)72 take the narrower
view, so as to exclude cases involving recognised wrongs.73 Interestingly, noneof the antagonists on this question take issue with one another about the basic
rules governing recovery, or the remedies that may be recovered, which may
explain why courts have not rushed in to resolve the taxonomic question. The
United Kingdom Supreme Court appears now to prefer the narrower view,74
and there is one obiter dictum in the High Court in Farah, which hints at thesame preference.75 The identification of unjust enrichment law with claims
involving ‘vitiated transfers’ also seems to be assumed by the High Court’s
approach in both David Securities76 and Equuscorp.77 On the other hand, there
71

Third Restatement (n 9) § 1 cmt (a).

72

Edelman and Bant (n 11) 19–21.

73

For the narrow view, see, eg, Keith Mason, JW Carter and GJ Tolhurst, Mason and Carter’sRestitution Law in Australia (LexisNexis Butterworths, 3rd ed, 2016) 43 [135]; Goff and Jones(n 11) 4–5; Birks, Unjust Enrichment (n 11) 274 (changing his mind on this point from Birks,
Introduction (n 17) 26); Graham Virgo, The Principles of the Law of Restitution (Oxford University Press, 3rd ed, 2015) 417–18. Andrew Burrows’ position is more complex — although
he describes unjust enrichment as a ‘cause of action’ distinct from wrongs (see below Part
II(E)), he nonetheless maintains that restitution for wrongs is based on an ‘underlying principle’ of unjust enrichment: Andrew Burrows, A Restatement of the English Law of Unjust
Enrichment (Oxford University Press, 2012) 26 § 1(3) (for the former proposition) (‘Restatement’); Andrew Burrows, The Law of Restitution (Oxford University Press, 3rd ed, 2011) 12(for the latter). My own preference for the broad view is iterated and explained further in
Barker, ‘Understanding the Unjust Enrichment Principle’ (n 28).

74

See, eg, Sempra Metals Ltd v Inland Revenue Commissioners [2007] 1 AC 561, 605–6 [116](Lord Nicholls), 649–50 [230]–[231] (Lord Mance); Benedetti (n 41) 959 [24](Lord Clarke JSC); Investment Trust (n 26) 295 [43] (Lord Reed JSC for the Court), holdingthat the purpose of unjust enrichment is to correct ‘normatively defective transfers of value’;Swynson (n 42) 326 [22] (Lord Sumption JSC for the Court). This view is shared by theeditors of Goff and Jones (n 11) 5 [1.04].

75

Farah (n 5) 156 [150] (Gleeson CJ, Gummow, Callinan, Heydon and Crennan JJ), citing
Edelman’s view that cases of breach of fiduciary duty are ‘foreign to unjust enrichment’:
James Edelman, ‘A Principled Approach to Unauthorised Receipt of Trust Property’ (2006)
122 (April) Law Quarterly Review 174, 178.

76

David Securities (n 20) 378 (Mason CJ, Deane, Toohey, Gaudron and McHugh JJ).

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are multiple indications in cases involving equitable wrongdoing and intellectual property torts that the purpose of an account of profits is to prevent anddeter the unjust enrichment of the wrongdoer.78 Bullen and Leake continues
to assume that cases of wrongdoing fall within the unjust enrichment category
for pleading purposes.79 The aims of gain-based remedies can clearly be
different in cases involving wrongdoing (encompassing deterrence as well as
corrective justice), but the question is whether this is a good enough reason tointerpret them as lying in an entirely separate legal category, or merely areason to identify them as a distinct subcategory of unjust enrichment law. I
tend toward the latter view on the basis that the cases have sufficient incommon to justify treating them as a ‘family’, even if relations between somefamily members are pretty remote.80 Part of the logic of keeping a family
together under the same roof is that differences between its constituent
members can be examined and properly worked out. This does not happen if
its more errant members are asked to leave.
A second point of controversy that is probably of greater concern to pleaders concerns which aspects of equitable doctrine and remedies lie within its
rubric. In Australia, it seems to be accepted that the category includes: many(but not all) claims involving the old common law counts of money had andreceived, money paid to another’s use, quantum meruit and quantum valebat;81 cases involving the equitable right to recover part payments of money
upon a failure of consideration;82 (perhaps) some claims for rescission;83 some77

Equuscorp (n 34) 516 [30] (citing David Securities), 517–18 [32] (citing Roxborough andFarah) (French CJ, Crennan and Kiefel JJ). See also Commissioner of State Revenue (Vic) v
Royal Insurance Australia Ltd (1994) 182 CLR 51, 75 (Mason CJ).

78

See, eg, Dart Industries Inc v The Decor Corp Pty Ltd (1993) 179 CLR 101, 111 (Mason CJ,
Deane, Dawson and Toohey JJ); Warman International Ltd v Dwyer (1995) 182 CLR 544, 557(Mason CJ, Brennan, Deane, Dawson and Gaudron JJ); Harris v Digital Pulse Pty Ltd 56
NSWLR 298, 331 [165], 332 [168]–[172] (Mason P), 383–4 [334] (Heydon JA); Ancient
Order of Foresters in Victoria Friendly Society v Lifeplan Australia Friendly Society Ltd (2018)
360 ALR 1, 22–3 [78] (Gageler J) (‘Ancient Order of Foresters’).

79

Blair et al, Bullen and Leake and Jacob’s Precedents of Pleadings (Sweet & Maxwell, 18th ed,2016) vol 2, 1047–9 [108-01]–[108-02].

80

As in life, so in law. See Barker, ‘Understanding the Unjust Enrichment Principle’ (n 28)
92–5, rejecting essentialist approaches to classification and concluding that ‘[u]njust enrichment law … is a mixed bag without being an incoherent bag’.

81

See, eg, Pavey (n 3) 227 (Mason and Wilson JJ); Westpac (n 55) 673 (Mason CJ, Wilson,
Deane, Toohey and Gaudron JJ); David Securities (n 20) 401 (Dawson J), citing Westpac(n 55); Mann (n 12) 38–9 [150] (Nettle, Gordon and Edelman JJ).

82

See, eg, MSD Securities Pty Ltd v MFB Properties (NQ) Pty Ltd [No 2] [2018] 2 Qd R 51,
86–7 [130]–[131] (Bond J); McDonald v Dennys Lascelles (1933) 48 CLR 457, 470 (Starke J),
citing Lexane Pty Ltd v Highfern Pty Ltd [1985] 1 Qd R 446, 454–5 (McPherson J).

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cases involving equitable liens (where the objective is to secure a restitutionary debt);84 and arguably (although more tenuously, because the language ofunjust enrichment is currently rarely used) a range of cases involving constructive trusts.85 Australian courts, like English ones,86 have to date rejected
the view that ‘presumed’ resulting trusts are restitutionary, on the hypothesisthat such trusts represent the implied intentions of the parties, not the failure
thereof.87 Furthermore, the High Court is not (yet) fully sold on the idea thatunjust enrichment provides the explanation for claims for equitable contribution,88 or non-consensual subrogation,89 and (consistently with the observations made above) it has commonly been asserted that such claims rest
83

Mason, Carter and Tolhurst (n 73) 556–7 [1305]. In the UK, see, eg, Pitt v Holt [2013] 2 AC108. Rescission has generally been regarded as a process in respect of a contract or deed that
occurs before restitution takes place, in order to strip away allocations of risk, but restitutionof money, property or the value of work then often follows on unjust enrichment grounds.
The key question is whether, in such instances, this is a distinct process, or part of rescission
itself.

84

See, eg, Young v ACN 081 162 512 (2005) 218 ALR 449; Atco Controls Pty Ltd (in liq) v
Stewart [2013] VSCA 132, [85] (Warren CJ), [185] (Redlich JA) (‘Atco’). The decision in Atco
was reversed on appeal in Stewart v Atco Controls Pty Ltd (in liq) (2014) 252 CLR 307,
334–5 [6] (Crennan, Kiefel, Bell, Gageler and Keane JJ) (on reasoning specific to the issue ofthe plaintiff ’s entitlement to a liquidator’s lien under the principle in Re Universal Distributing Co Ltd (in liq) (1933) 48 CLR 171).

85

See, eg, Muschinski (n 30) 612, 616–17 (Deane J); Baumgartner v Baumgartner (1987) 164
CLR 137, 149 (Mason CJ, Wilson and Deane J); Bryson v Bryant (1992) 29 NSWLR 188, 209(Kirby P); Wambo (n 43); Break Fast Investments Pty Ltd v Giannopoulos [No 5] [2011]
NSWSC 1508; Re Wan Ze Property Development (Aust) Pty Ltd (2012) 90 ACSR 593,
605–6 [51]–[52] (Black J) (Supreme Court of New South Wales); Thorn v Boyd [2016]
NSWSC 1344, [81] (Sackar J); Zuecker v Bruggmann [No 3] [2017] QSC 259, [124] (Bond J).

86

Westdeutsche Landesbank Girozentrale v Islington London Borough Council [1996] AC 669,
689–90 (Lord Goff), 708–9 (Lord Browne-Wilkinson).

87

Raulfs v Fishy Bite Pty Ltd [2012] NSWCA 135, [44]–[51] (Campbell JA, Meagher agreeingat [113], Barrett JA agreeing at [114]).

88

See, eg, Friend (n 37) 134 (French CJ, Gummow, Hayne, Heydon and Bell JJ); HIH Claims
Support Ltd v Insurance Australia Ltd (2011) 244 CLR 72, 87–90 [36]–[48] (Gummow ACJ,
Hayne, Crennan and Kiefel JJ); Lavin v Toppi (2015) 254 CLR 459, 469 [32] (French CJ,
Kiefel, Bell, Gageler and Keane JJ). But see at 471 [41]. See also JD Heydon, MJ Leeming and
PG Turner, Meagher, Gummow and Lehane’s Equity: Doctrine and Remedies (LexisNexis
Butterworths, 5th ed, 2015) 398–9 [10-040]. This position contrasts with rationalisations ofcontribution claims under some statutory provisions: see, eg, James Hardie & Co Pty Ltd v
Wyong Shire Council (2000) 48 NSWLR 679, 686 [36] (Handley JA); Lukey v Corporate Investment Australia Funds Management Pty Ltd [2005] FCA 298, [335] (Emmett J).

89

Bofinger (n 5). Although, interestingly, reference to unjust enrichment is made:at 299–300 [88] (Gummow, Hayne, Heydon, Kiefel and Bell JJ). For a view representative of
this position, see Mark Leeming, ‘Subrogation, Equity and Unjust Enrichment’ in Jamie
Glister and Pauline Ridge (eds), Fault Lines in Equity (Hart Publishing, 2012) 27, 40.

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instead on established principles of equity, unconscionability, the fair sharingof obligations between the parties, or ‘natural justice’.90 These objections
rather miss the point that there is, in fact, no taxonomic clash between equity
and unjust enrichment because the former category is drawn along historic,
jurisdictional lines, and the latter along substantive ones.91 It is perfectly
possible for a claim to be one for unjust enrichment, to be equitable injurisdictional origin, and to be just in the natural law (moral) sense.
Leaving these matters aside for now, the more pressing question is whether
the plurality judgment of the High Court in Hills has now rejected any
taxonomic role for the concept. Extraordinarily, the Victorian Court ofAppeal appears recently to have thought so, concluding (in obiter dicta) in
Vescovi that the High Court
has rejected the idea that unjust enrichment is the overarching legal genus ofwhich, for example, payment under a mistake or failure of consideration or duress or undue influence or demands made without authority are merely
species.92

This conclusion appears, with respect, to be a misinterpretation of a particularparagraph in the plurality judgment, in which the High Court was considering arguments about the way in which the new defence of change of position
should operate in restitutionary claims in Australian law. In the relevant
passage, the plurality rejected the idea that this defence operates only to theextent that defendants can prove that that they have lost the enrichment
received with mathematical exactitude. Their Honours concluded instead thatthe key inquiry is whether a defendant has, on the faith of the receipt,
sustained a detriment that it would be inequitable to force him or her to bear:[The plaintiff ’s] approach focuses upon the extent to which Hills and Boschhave been ‘disenriched’ subsequent to the receipt. This approach seeks to giveeffect to an understanding of unjust enrichment as a principle of direct application, which operates by measuring the extent of enrichment or, where a defenceof change of position is invoked, the extent of disenrichment subsequent to that
90

See, eg, Burke v LFOT Pty Ltd (2002) 209 CLR 282, 294 [22] (Gaudron ACJ and Hayne J);
Albion Insurance Co Ltd v Government Insurance Office (NSW) (1969) 121 CLR 342, 351(Kitto J); Mahoney v McManus (1981) 180 CLR 370, 378 (Gibbs CJ), 385 (Wilson J).

91

Peter Birks, ‘Equity in the Modern Law: An Exercise in Taxonomy’ (1996) 26(1) University ofWestern Australia Law Review 1, 67.

92

Vescovi (n 61) 394 [45] (Warren CJ, Santamaria JA and Ginnane AJA). Although thisinterpretation was based on the Court’s interpretation of the High Court’s view in ‘several
cases’, it clearly took Hills to instantiate that view.

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receipt. Such a ‘principle’ does not govern the resolution of this case because
the concept of unjust enrichment is not the basis of restitutionary relief in Australian law. The principle of disenrichment, like that of unjust enrichment, isinconsistent with the law of restitution as it has developed in Australia. Disenrichment operates as a mathematical rule whereas the inquiry undertaken in
relation to restitutionary relief in Australia is directed to who should properly
bear the loss and why. That inquiry is conducted by reference to equitable principles.93

The assertion in this extract that the principle of unjust enrichment is ‘not thebasis of restitutionary relief in Australian law’ was clearly not necessary for
the way in which the Court chose to formulate the change of position defence.
It is best interpreted simply as proscribing the use of the concept in the fifth
possible role described below — as a definitive cause of action. This interpretation is consistent with the Court’s assertion in the second extracted sentencethat the principle is not one of ‘direct application’ and coheres also with theHigh Court’s past approval of the idea as a useful developmental tool andunifying concept.94 It is a more credible interpretation, I suggest, than theview that the Court intended to rule out the idea that there is any such
category as unjust enrichment law in Australia, even accepting that there arestill debates about the subject’s precise boundaries.95
The cautious conclusion of this section is therefore that the concept ofunjust enrichment does refer to a particular body of law in Australia, as well as
operating as a device for the development of the rules that fall within it. At its
core are those cases involving the old praecipe writs and the money counts
that came to be known by the unfortunate title of ‘quasi-contract’, but it clearlyextends beyond these instances. Depending on the answers to the twoquestions identified above, it is either broader or narrower (I suggest broader), but in either case it contains a range of causes of action in respect of gains
that one person has made at the expense of another, drawing those categories
together for analysis in a way that crosses traditional jurisdictional boundaries, but which is not insensitive to the different contexts in which the various
rules have developed. Because the category contains a mixture of different
causes of action for unjust gain, it resembles the law of torts more than it does
93

Hills (n 7) 596–7 [78] (Hayne, Crennan, Kiefel, Bell and Keane JJ) (emphasis in original).

94

See above nn 30–4 and accompanying text.

95

For a similar conclusion, see Edelman and Bant (n 11) 25–6. Note also that the taxonomic
function of the concept has recently been reiterated by the judgment of the (differently constituted) plurality of the High Court in Mann: see above n 69 and accompanying text.

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the law of contract.96 For this reason too, it is probably best to refer to it as ‘thelaw of unjust enrichments’, or (perhaps) ‘the laws of unjust enrichment’, rather
than ‘the law of unjust enrichment’. The latter title carries a vague implicationthat the category is based on a singular legal proscription, which it is not.
Instead, the category comprises a congery of rules that share a number ofimportant family resemblances,97 but which lack any single, ‘essential’ quality
beyond the fact that all the claims in question are for gains made by adefendant, not losses suffered by the plaintiff.
D Role 4: An Analytical Framework
A fourth role for the idea of unjust enrichment, which sits comfortably withthe third, is that it can provide a framework for the analysis of the various
claims that fall within the category just described. In England and Wales, thisanalytical role is now clearly accepted. In Banque Financière de la Cité v Parc
(Battersea) Ltd (‘Banque Financière’),98 Lord Steyn hence suggested that four
analytical questions arise that are common to all cases of unjust enrichment:
1 Has [the defendant] benefited or been enriched?
2 Was the enrichment at the expense of [the plaintiff]?
3 Was the enrichment unjust? and4 Are there any defences?99
To this, it is common to add a fifth analytical question, namely:
5 What is the nature of the remedy provided — personal or proprietary?100
Lord Steyn’s approach has been endorsed several times by the United Kingdom Supreme Court.101 The various analytical questions are not akin to the96

See Steven A Smith, ‘Unjust Enrichment: Nearer to Tort than Contract’ in Robert Chambers,Charles Mitchell and James Penner (eds), Philosophical Foundations of the Law of Unjust
Enrichment (Oxford University Press, 2009) 181.

97

For an exposition of this conception of unjust enrichment with Wittgenstein’s theory offamily resemblance, see Barker, ‘Understanding the Unjust Enrichment Principle’ (n 28)
92–5.

98

Banque Financière (n 42).

99

Ibid 227. See also at 234 (Lord Hoffmann).

100

Justice Keith Mason, ‘What Has Equity to Do with Restitution? Does It Matter?’ (2007) 15
Restitution Law Review 1, 1 (‘What Has Equity to Do with Restitution?’). See Investment
Trust (n 26) 294 [38] (Lord Reed JSC).

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precise requirements of a single cause of action, but are, rather, ‘broad
headings’ which assist in expounding and structuring courts’ approach to avariety of different restitutionary claims. This was explained by Lord Reed in
Investment Trust Companies v Revenue and Customs Commissioners (‘Investment Trust’)102 in the following, pellucid way:
Lord Steyn’s four questions are no more than broad headings for ease of exposition. They are intended to ensure a structured approach to the analysis of unjust enrichment, by identifying the essential elements in broad terms. If they
are not separately considered and answered, there is a risk that courts will resort to an unstructured approach driven by perceptions of fairness, with consequent uncertainty and unpredictability. At the same time, the questions are notthemselves legal tests, but are signposts towards areas of inquiry involving a
number of distinct legal requirements. In particular, the words ‘at the expenseof ’ do not express a legal test; and a test cannot be derived by exegesis of thosewords, as if they were the words of a statute.
The structured approach provided by the four questions does not, therefore,
dispense with the necessity for a careful legal analysis of individual cases.103

This analytical framework has not, as yet (or in full), been unanimously
adopted by the High Court of Australia. In Roxborough, Kirby J described thefour-stage approach as ‘generally accepted’,104 but this was probably an
exaggeration of the views of the High Court Bench itself at that time. However, more recently in Equuscorp, the High Court accepted and applied what it
called an ‘approach to determining’ unjust enrichment claims which operates
at a ‘fairly high level of abstraction’ and which has two analytical stages: theestablishment of an enrichment that is prima facie unjust by reference torecognised classes of qualifying or vitiating factors; and the identification of
circumstances (defences) which displace that prima facie liability by establishing that an order for restitution would be unjust.105 This analysis was based on
101

See, eg, Benedetti (n 41) 955 [10] (Lord Clarke JSC, Lords Kerr JSC and Wilson JSC
agreeing); Menelaou (n 42) 187–8 [18]–[19] (Lord Clarke JSC, Lord Neuberger PSC agreeing
at 197 [61], Lords Kerr and Wilson JJSC agreeing at 218 [141]); Eastenders (n 24) 41 [102](Lord Toulson JSC for the Court); Investment Trust (n 26) 295 [41] (Lord Reed JSC for the
Court). See also Investment Trust Companies (in liq) v Revenue and Customs Commissioners[2012] STC 1150, 1167 [38] (Henderson J) (England and Wales High Court, Chancery
Division).

102

Investment Trust (n 26).

103

Ibid 295 [41]–[42].

104

Roxborough (n 5) 568 [139] n 257.

105

Equuscorp (n 34) 516 [30] (French CJ, Crennan and Kiefel JJ).

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the decision in David Securities,106 and features also in the judgment ofGageler J in Hills.107 It clearly only needs to be pressed very slightly to divulge
the full and greater range of questions posed by Lord Steyn, and a detailed
examination of the relevant passage suggests that it is in fact a compressed
expression of the first four stages of the above analysis. In Mann, the plurality
seems clearly to have accepted the utility of that four-stage approach as ameans of structuring our understanding of restitutionary claims.108 The fivestage approach has been advocated by Justice Keith Mason, writing extracurially.109 There is also an extraordinarily wide range of authority in lower courts
in which some or all five parts of the analytical framework have been used inlegal reasoning in recent years.110 The function of the framework can beunderstood as analogous to that of the ‘Caparo’ framework (note — framework, not test) that is used in the United Kingdom to rationalise and deter-

106

David Securities (n 20) 379 (Mason CJ, Deane, Toohey, Gaudron and McHugh JJ). The twostage approach in David Securities was itself based on Westpac (n 55) 673 (Mason CJ, Wilson,
Deane, Toohey and Gaudron JJ).

107

Hills (n 7) 617 [136].

108

Mann (n 12) 61–2 [213] (Nettle, Gordon and Edelman JJ). Note, however, the point that theelements of the analytical framework cannot be used dispositively as definitive elements of a
restitutionary cause of action.

109

See Mason, ‘What Has Equity to Do with Restitution?’ (n 100) 1; Justice Keith Mason,‘Where Has Australian Restitution Law Got to and Where Is It Going?’ (2003) 77(6) Australian Law Journal 358, 361–3.

110See, eg, Koorootang Nominees Pty Ltd v Australia and New Zealand Banking Group Ltd [1998]
3 VR 16, 102 (Hansen J) (stages 1–3); Torpey Vander Have Pty Ltd v Mass Constructions Pty
Ltd (2002) 55 IPR 542, 549 [34] (Spigelman CJ) (New South Wales Court of Appeal) (stages
1–3); Spangaro v Corporate Investment Australia Funds Management Ltd (2003) 54 ATR 241,
256 [48] (Finkelstein J) (Federal Court) (stages 1–4); Farah (Court of Appeal) (n 44) [223](Tobias JA for the Court) (stages 1–3 described as ‘factors’: at [224]); Ideas Plus Investments
Ltd v National Australia Bank Ltd (2006) 32 WAR 467, 485–6 [65] (Steytler P, Buss JA agreeing at 500 [113]), 496 [96] (McLure JA) (stages 1–4); Ethnic Earth Pty Ltd v Quoin Technology
Pty Ltd (in liq) [No 3] (2006) 94 SASR 103, 117 [65] (Bleby J) (stages 1–3); Lumbers (FullSupreme Court) (n 58) 420 [63] (Sulan and Layton JJ) (stages 1–4); Australian Financial
Services and Leasing Pty Ltd v Hills Industries Ltd [2011] NSWSC 267, [21]–[23] (Einstein J)(‘Hills (Supreme Court)’) (stages 1–4); Henderson v McSharer [2013] FCA 414, [73] (Barker J)(stages 1–3); Focus Metals Pty Ltd v Babicci [2014] VSC 380, [120]–[121] (Sloss J) (stages
1–4), citing Hills (Supreme Court) (n 110) [21] (Einstein J) (in respect to stages 1–3), David
Securities (n 20) 380 (Mason CJ, Deane, Toohey, Gaudron and McHugh JJ) (in respect tostage 4); Lampson (n 41) [51]–[55] (Edelman J) (stages 1–4); A & A Martins Pty Ltd v Liu[2018] ACTSC 102, [25]–[26] (McWilliam AsJ) (‘A & A Martins’) (stages 1–5); Gambaro Pty
Ltd v Rohrig (Qld) Pty Ltd [2018] QCA 327, [18] (Sofronoff P, Philippides JA agreeing at [31],Boddice J agreeing at [32]) (‘Gambaro’) (stages 1–3); Burkett v Bendigo and Adelaide Bank
Ltd [No 2] (2018) 133 ACSR 411, 441 [104] (Croft J) (Supreme Court of Victoria) (‘Burkett’)(stages 1–4).

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mine novel duty of care questions.111 It is subject to the same methodologicallimitations and is consistent with the normal, incremental process of development in common law systems.
Here we must unfortunately return to Vescovi, because the Victorian Courtof Appeal in that decision appears to have interpreted the plurality judgmentin Hills, discussed above, as not simply ruling out the idea of unjust enrichment as an overarching category or ‘genus’ of law, but as also precluding
Australian courts from making any use of the above-mentioned analyticalframework.112 This construction of Hills is, I suggested above, a misinterpretation of the plurality’s intention, which seems to have been to rule out the useof unjust enrichment as a dispositive norm or cause of action, not the use of
the idea in an organisational, analytical role. It has thankfully not been
followed by other Australian courts, which have continued to refer to parts of
the analytical framework even after the decision in Hills was handed down.113
Sadly, the confusion surrounding paragraph 78 in Hills has given rise toother, distinct analytical mistakes. For example, both Victorian and Queensland courts have recently cited the judgment as authority for the suggestionthat unjust enrichment claims can have completely different analyticalelements in different types of case. In Sunwater Ltd v Drake Coal Pty Ltd(‘Sunwater’),114 the Queensland Court of Appeal hence concluded that, incases of unjust enrichment in which a plaintiff is seeking to recover the valueof work done, as opposed to money paid, it is unnecessary for a court toconsider whether there might be any defence of change of position, or othercircumstances making it inequitable to require a defendant to pay restitution.
This assertion was made, in part, on the basis that Hills has confirmed thatunjust enrichment is not a ‘definitive legal principle’.115 Philippides JA alsosuggested that it is unnecessary and inappropriate to consider even whether

111

For a full explanation of the way this approach is to be understood, see Robinson v Chief
Constable of West Yorkshire Police [2018] AC 736, 744–7 [21]–[30] (Lord Reed JSC, BaronessHale PSC and Lord Hodge JSC agreeing).

112

Vescovi (n 61) 395 [48]–[49] (Warren CJ, Santamaria JA and Ginnane AJA), where the Court
ruled out reference to either the three- or five-stage approach.

113

See, eg, A & A Martins (n 110) [25]–[26] (McWilliam AsJ) (stages 1–5); Gambaro (n 110)[18] (Sofronoff P) (stages 1–3); Burkett (n 110) 441 [104] (Croft J) (stages 1–4); Mann (n 12)
61–2 [212]–[213] (Nettle, Gordon and Edelman JJ) (stages 1–4).

114[2017] 2 Qd R 109 (‘Sunwater’).

115

Ibid 120 [36] (Phillip McMurdo JA, Gotterson JA agreeing at 111 [1], Philippides JA agreeing
at 111 [2]).

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the defendant benefitted by the work done, in such a case.116 Since the various
restitutionary causes of action that comprise the category of unjust enrichment law are distinct from one another, they have, her Honour reasoned,‘distinct elements and defences’ that should not be ‘transplanted’ across
categorical lines.117 The apparent consequence of this approach is that at least
two of the identified five elements of the unjust enrichment framework canmagically disappear as one moves from one type of case (involving money) toanother (involving work), when the only difference between them lies in thetechnical form of the benefit received.
This conclusion is unfortunate and threatens to undermine the utility of
the framework as a way of guiding judges in a stable way through the relevant
forms of inquiry. A better view, which is still consistent with the rules
currently governing the recovery of remuneration for work done, is simply
that, where a request for the work has been proven and the work meets therequest, the defendant should be presumed to have benefitted at the plaintiff ’s
expense, not that the existence of such a benefit is irrelevant to the unjust
enrichment claim. Indeed, the suggestion that an unjust enrichment claim candispense with the requirement that a defendant be enriched is curiously
paradoxical and maladroit. Similarly, whilst it is perhaps less likely that adefence of change of position will apply where a defendant has requested
work than when he or she has innocently received and spent money, thelogical possibility of defendants detrimentally changing their position inconsequence of the provision of work, such that it would be inequitable torequire full payment for it, cannot and should not be ruled out.
Woolcorp Pty Ltd v Rodger Constructions Pty Ltd118 provides a second, lessserious example of the same tendency to fragment and abandon parts of thestandard analytical framework in cases involving the provision of work.
Whilst the Court on this occasion did not go so far as to suggest that theexistence of a benefit is irrelevant in this type of unjust enrichment claim,
their Honours did suggest that where work is requested, it is still ‘inappropriate to … consider’ whether it was received at the plaintiff ’s expense (thesecond analytical question).119 This was again on the basis that the law ofrestitution ‘does not necessarily involve any set list of factors in determining
116

Ibid 114–15 [17], citing Hendersons Automotive Technologies Pty Ltd (in liq) v Flaton
Management Pty Ltd (2011) 32 VR 539, 553 [60]–[62] (Tate JA, Ashley JA agreeing
at 541 [1], Neave JA agreeing at 541 [2]) (‘Hendersons’).

117

Sunwater (n 114) 115 [19].

118[2017] VSCA 21.

119

Ibid [12] (Santamaria, Kyrou and Elliott JJA).

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whether a claim has been made out’.120 The better view again seems to be that,
where D has requested work and that request has caused P to provide it to D,
the work can be presumed to have been provided at P’s expense, without
further evidence needing to be adduced. The point is again not that one of theanalytical stages is irrelevant, but that it is in practice easily met and need not
greatly occupy the court’s time. A benevolent reading of the case suggests that
this may have been what the Court really intended to say.
The important point of the fivefold unjust enrichment framework is hence
not that each question it posits has to be answered in the same way in allcases, but rather that each of the questions it identifies must be considered ineach case. If the framework is to provide a useful, stabilising function in
respect of the development and understanding of the modern law, it must be
used in all unjust enrichment cases, not just some. Whilst it is acceptable,
therefore, to suggest that some of the questions it raises are likely to beanswered straightforwardly in particular categories of case, or even answeredin different ways, this does not mean that the questions themselves cease to be
relevant questions, or that the basic elements of an unjust enrichment claim
differ completely as between different types of case.
Many of these problems are the residual product of the preference of the
majority of the High Court in Lumbers v W Cook Builders Pty Ltd (in liq)(‘Lumbers’)121 and other cases in the early part of the new millennium foranalysing restitutionary claims through the traditional desiderata of the oldprocedural forms of action, in preference to reasoning in terms consistent
with modern unjust enrichment analysis. This has led to the hiving off ofclaims for work done into a separate, historical analytical framework and an
attendant assumption that a request by the defendant is the only analytical‘element’ of a claim in such a case, which is both necessary and sufficient forthe claim’s success.122 In fact, although the presence of such a request is highly
relevant and undoubtedly likely to result in a claim succeeding, this is because
the request assists in establishing conclusively both the fact of the defendant’s
enrichment and the injustice of a defendant not paying for it. It is not becausea ‘request’ for the work is the sole ‘element’ of the claim. Furthermore, theabsence of such a request cannot be taken to be conclusive against the successof an unjust enrichment claim, since a defendant’s enrichment by the work,

120

Ibid.

121

Lumbers (n 34) 662–5 [78]–[85] (Gummow, Hayne, Crennan and Kiefel JJ).

122

See, eg, Sunwater (n 114) [17]–[18] (Philippides JA), citing Hendersons (n 116) 553 [60]–[62](Tate JA, Ashley JA agreeing at [1], Neave JA agreeing at [2]).

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Melbourne University Law Review[Vol 43(3):Advand the injustice of his or her not paying for it, could potentially be established in other ways.123
What this demonstrates is that, although progress is gradually being made,we are still at a stage in Australia at which courts and practitioners aretransitioning from modes of legal analysis that are historical and based on theformulae of the old writ actions, to the new mode of analysis, which focuseson the substantive requirements of underlying restitutionary rights. The
sooner the former is finally abandoned, the better.
E Role 5: A Cause of Action?
It will be evident from what has been said in the previous sections that theHigh Court’s key modern concern relates to the idea that the concept ofunjust enrichment might itself provide a cause of action, by which I havesuggested the Court means a definitive norm which can be applied directly tothe facts of a particular case in order to generate legal outcomes. The conceptof a cause of action is slippery, but for current purposes I take the idea to referto the set of factual conditions which is both necessary and sufficient to giverise to a legal claim.124 Practitioners are necessarily acutely concerned to
identify the cause of action accurately in any given case, precisely because thisdetermines the facts that they must plead. As we shall see in the final section,
confusion about the precise identity of the relevant ‘cause of action’ inrestitutionary claims has resulted in recent years in a number of defective
pleading practices, with some plaintiffs being forced to seek leave to amend,or having their claims struck out.
The view that unjust enrichment is not itself a cause of action in the defined sense was clear from the start. Dawson J expressly said as much, and inthese terms, in David Securities125 and other members of the Court in that123

For example, by demonstrating that the benefit was rendered in circumstances of necessity (apossibility acknowledged in Lumbers (n 28) 663–4 [80] (Gummow, Hayne, Crennan andKiefel JJ)) or that it was freely accepted by the defendant. Although Lumbers is sometimes
interpreted as inconsistent with the latter proposition, it is still very much alive: see Barker
and Grantham (n 11) 94.

124

Letang v Cooper [1965] 1 QB 232, 242–3 (Diplock LJ): a cause of action is ‘a factual situation
the existence of which entitles one person to obtain from the court a remedy’. On the complexities, see also Silas A Harris, ‘What Is a Cause of Action?’ (1928) 16(6) California Law
Review 459; Lionel Smith, ‘Sources of Private Rights’ in Simon Degeling, M Crawford andNicholas Tiverios (eds), Justifying Private Rights (Hart Publishing, forthcoming).

125

David Securities (n 20) 406. See also Burkett (n 110) 441 [103] (Croft J), citing Lumbers(n 34), Pavey (n 2).

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case were, I suggest, making the same point when they said that the principle
is not ‘definitive … according to its own terms’.126 That analysis has been
repeated by the High Court ad nauseam127 and is, I have posited above, at thecore of the plurality’s assertion in Hills that the idea of unjust enrichment is
not capable of ‘direct application’ and does not provide ‘the basis’ of restitutionary relief in Australian law’.128 In Lampson, Edelman J interestingly
clarified and qualified the last proposition by saying that it is not the ‘direct
basis’ of restitutionary relief,129 by which he was probably intending topreserve the idea that, although it is not a cause of action, it plays a remoter,taxonomic and organisational role. The same view seems to lie at the root ofCampbell J’s observation in the earlier case of Wasada that unjust enrichment
is an ‘explanatory concept’, but that, because it is not actually a singular causeof action, one needs always to ‘look to other legal standards to find out
what … [it] is’.130
The consequence of this is that whilst all unjust enrichment claims can beanalysed through the framework identified in the previous section, eachseparate claim nonetheless comprises a distinct cause of action in its own
right, and each cause of action has its own specific rules and requirements.
The category of unjust enrichment law is a collection of individual causes ofaction. Each cause of action in the category can hence legitimately be described as a claim ‘in’ unjust enrichment (just as a claim for negligence or false
imprisonment is a claim ‘in tort’), but unjust enrichment is not ‘a’ cause ofaction in itself any more than ‘tort’ is ‘a’ cause of action.131
126

David Securities (n 20) 378 (Mason CJ, Deane, Toohey, Gaudron and McHugh JJ).

127

See, eg, Farah (n 5) 156 [151] (Gleeson CJ, Gummow, Callinan, Heydon and Crennan JJ);
Bofinger (n 5) 299 [86] (Gummow, Hayne, Heydon, Kiefel and Bell JJ); Equuscorp (n 34)
515–16 [29] (French CJ, Crennan and Kiefel JJ); Mann (n 12) 61–2 [212]–[213] (Nettle,
Gordon and Edelman JJ). See also Wasada (n 23) [18], [22] (Campbell J).

128

Hills (n 7) 596 [78] (Hayne, Crennan, Kiefel, Bell and Keane JJ). See also Lumbers (n 34),
where it was stated that the principle is not a ‘sufficient premise for direct application inparticular cases’: at 665 [85]–[86] (Gummow, Hayne, Crennan and Kiefel JJ).

129

Lampson (n 41) [50] (emphasis added).

130

Wasada (n 23) [22] (emphasis added). By ‘other legal standards’, his Honour is probablyreferring to the lower-level, concrete legal rules which, along with the required facts, constitute the plaintiff ’s ‘cause of action’.

131

For this reason, Professor Burrows makes it clear that if one refers to unjust enrichment as a‘cause of action’, it can only be as a generalising proposition (like saying that ‘tort’ is a cause ofaction), not a cause of action in the key, specific sense identified in this article: Burrows,
Restatement (n 73) 26 § 1(3). For a recent conversion to a view close to that provided in thisarticle, see Lionel Smith, ‘Defences and the Disunity of Unjust Enrichment’ in Andrew Dyson, James Goudkamp and Frederick Wilmot-Smith (eds), Defences in Unjust Enrichment

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Melbourne University Law Review[Vol 43(3):AdvA list of the causes of action in unjust enrichment law includes thosenamed long ago by Lord Mansfield in Moses.132 Most are well known andaccurately identified in the main texts.133 They include mistake, failure of basis(consideration or condition), personal incapacity, duress, legal compulsion,
undue influence (in its various forms), unconscionable dealing, the ‘free
acceptance’ of a benefit,134 and absence of consent or want of authority inrespect of the bestowal of a benefit (sometimes alternatively referred to ascases of ‘ignorance’ or cases in which the plaintiff had ‘no intention’ to make atransfer). They may also include some public policy grounds, such as illegality, and the rule in England and Wales that there should be no taxation
without the authority of Parliament.135 Depending on how broadly theboundaries of the unjust enrichment category are drawn, they may also
include wrongs, including a number of torts, breaches of confidence, breachesof fiduciary duty, the breach of some types of contract,136 and accessorial
equitable wrongs. Claims for the gains made by a defendant in each of thesecircumstances necessarily require the injustice of the defendant’s enrichment
to be proven in different ways, in accordance with well-known principles thathave been worked out by courts over a long period of time. A claim formoney paid on a basis that has failed hence currently still formally requires
proof that the basis has failed in total,137 with some (growing) exceptions.138 A(Hart Publishing, 2016) 27. For the suggestion that this is now probably also the position of
the Supreme Court of Canada, see Lionel Smith, ‘The State of the Law of Unjust Enrichment
in Common Law Canada’ (2015) 57(1) Canadian Business Law Journal 39.
132

Moses (n 53) 680–1 [1012].

133

See, eg, Mason, Carter and Tolhurst (n 73).

134

R v Vale of White Horse District Council [2003] EWHC 388, [14] (Lightman J). In Australia,
the position is less clear in the light of Lumbers, but still arguable: Liebe v Molloy (1906) 4
CLR 347, 353–4 (Griffith CJ for the Court); Lampson (n 41) [90] (Edelman J).

135

Woolwich Equitable Building Society v Inland Revenue Commissioners [No 2] [1993] AC 70.

136

Restrictive covenants are the main example: see the line of cases running from Wrotham Park
Estate Co v Parkside Homes Ltd [1974] 1 WLR 798 (England and Wales High Court, Chancery Division). But see A-G v Blake [2001] 1 AC 268, 284 (Lord Nicholls) (‘Blake’). In One
Step (Support) Ltd v Morris-Garner [2019] AC 649 (‘One Step’), the United Kingdom Supreme Court has now cast doubt on the restitutionary analysis of negotiating damages incases of the former type. Blake survives, but is confined to its exceptional circumstances: at
685–6 [82] (Lord Reed JSC, Baroness Hale PSC, Lords Wilson and Carnwath JJSC agreeing).

137

Baltic Shipping (n 58) 350 (Mason CJ), 377–8 (Deane and Dawson JJ), 386 (Gaudron J), 389(McHugh J).

138

See, eg, David Securities (n 20) 383 (Mason CJ, Deane, Toohey, Gaudron and McHugh JJ).
See also James Edelman, ‘Restitution for a Total Failure of Consideration: When a Total
Failure Is Not a Total Failure’ (1996) 1(3) Newcastle Law Review 57, 61–2; Frederick WilmotSmith, ‘Reconsidering “Total” Failure’ (2013) 72(2) Cambridge Law Journal 414, 420–2.

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claim based on mistaken payment requires proof that the mistake wascausative of the payment. A claim based on duress requires proof both that agiven threat was causative of payment and that the relevant threat was
illegitimate. And so on. The requirements of each of these distinct causes ofaction can nonetheless be structured or analysed within the broader framework identified in the previous section.
I II I M P L I C AT I O N S F O R T H E P L E A D I N G O F C L A I M S
Whilst it is not necessary for parties to specify the legal cause of action uponwhich they rely in their pleadings, they must always plead the facts material totheir case.139 There is unfortunately little detailed guidance available inAustralia on pleading unjust enrichment claims,140 and confusions as towhether or not unjust enrichment itself constitutes a cause of action and, if
not, which restitutionary causes of action belong within the category, haveadded to the difficulties practitioners and individual litigants have experienced.
It follows from the conclusion in the preceding section that unjust enrichment is not itself ‘a cause of action’ in Australia, so that it is insufficient
simply to plead that a defendant has been unjustly enriched, or indeedvaguely to assert that each of the elements of an unjust enrichment claim
described in Part II(D) is made out. Pleadings of this sort will swiftly be
struck out.141 For a claim within the category to succeed, precise facts
establishing each of the relevant elements of a restitutionary cause of action(the first three elements of the five-stage analysis of all such claims) must be
asserted.142 They must therefore show not just that the defendant has beenenriched at the plaintiff ’s expense in a relevant and established sense, but also

139

See, eg, Supreme Court (General Civil Procedure) Rules 2015 (Vic) r 13.02(1)(a).

140

In England, Blair et al (n 79) provide precedents for some monetary restitutionary claims,
claims for benefits provided under discharged or ineffective contracts, claims for contribution and recoupment, restitution for torts and breaches of fiduciary duty and (in separate
sections) tracing, rescission and accounts, as well as some restitutionary defences, but therange is by no means complete: at 1047–69. In Australia, see generally Mason, Carter andTolhurst (n 73) ch 29; AG Nevill and AW Ashe, Equity Proceedings with Precedents: New
South Wales (Butterworths, 1981); Edmund Finnane, Christopher Wood and Nicholas Newton, Equity Practice and Precedents (Thomson Reuters, 2nd ed, 2019).

141

See, eg, Lactos Fresh Pty Ltd v Finishing Services Pty Ltd [No 2] [2006] FCA 748, [111](Weinberg J); ABL Custodian Services Pty Ltd v Smith [2010] VSC 548, [55] (Croft J).

142

Winterton (n 40) 375–6 (Gummow J).

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that there is a sufficient, specific ground for restitution, or ‘unjust factor’143 at
the third stage of the analysis. In the absence of such pleaded facts, broad
assertions that it would be unconscientious for the defendant not to pay for abenefit will not suffice. The point was put in the following way by Edelman J
in 2012:The presence of an unjust factor is an indispensable requirement to demonstrate the facts upon which a plaintiff relies for a claim that a defendant had no‘right to retain’ the benefit and was unjustly enriched. The unjust factor may also affect the availability or scope of defences, such as change of position, which
rely upon pleading facts which fall within established and developing rules
concerning circumstances which reduce or extinguish a defendant’s duty tomake restitution by ‘any matter or circumstance which shows that his or her receipt (or retention) of the payment is not unjust’.144

Precisely what is required to establish a restitutionary cause of action inunjust enrichment law hence depends always on the type of case in question.
To show a cause of action in a case of mistaken payment, the relevant mistaken belief and its causative effect must be asserted alongside the details of thepayment.145 If the plaintiff wants a proprietary remedy in respect of themoney paid, he or she must probably, on the state of the current law, plead
facts which show that the defendant had knowledge of the mistake.146 In acase of failure of basis, the relevant condition subject to which the benefit wasprovided, and the facts establishing that the condition or purpose has failed
must be asserted, together with the fact that the defendant was aware of therelevant condition, so that it was within both parties’ contemplation.147 In any
case in which a benefit has been provided under a contract, it will also benecessary to plead facts demonstrating that the contract is invalid, incomplete, has been rescinded or discharged, or is otherwise void or voidable, so as
143

Farah (n 5) 156 [150] (Gleeson CJ, Gummow, Callinan, Heydon and Crennan JJ); Equuscorp(n 34) 516 [30] (French CJ, Crennan and Kiefel JJ); Chidiac v Maatouk [2010] NSWSC 386,
[216] (Ward J) (‘Chidiac’); Hightime Investments Pty Ltd v Adamus Resources Ltd [2012]
WASC 295, [183]–[185] (Edelman J) (‘Hightime Investments’).

144

Hightime Investments (n 143) [185] (citations omitted).

145

Lahoud v Lahoud [2010] NSWSC 1297, [168], [176]–[179] (Ward J). Where multiple
overpayments are alleged to have been mistakenly made by a plaintiff on different dates forthe same reason, it is not always necessary to plead each individual payment as opposed to
the global amount, provided the defendant is not surprised at trial: Sturesteps v Khoury[2015] NSWSC 1041, [74] (Slattery J).

146

Wambo (n 43). The logic of this requirement is not obvious.

147

Roxborough (n 5) 526 [17] (Gleeson CJ, Gaudron and Hayne JJ).

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to negate the defendant’s legal right to the benefit and displace any concernthat restitution will undermine a valid contractual allocation of risk.148 In
cases involving wrongful enrichment, where a part of the plaintiff ’s cause ofaction resides in the wrong itself, it will normally be sufficient to prove facts
establishing that the defendant breached a relevant149 legal or equitable duty
owed to the plaintiff, and that the gain in question was factually and legallycaused by the breach.150 Despite the language that has featured in the High
Court, to which we alluded in Part II(B) above, it should not be necessary, tomake out a claim, to plead facts that show the inequity of allowing a defendant to retain the relevant enrichment, since such facts are relevant only toestablishing a restitutionary defence.
Undoubtedly the most common failing in modern pleading practices has
been the failure to specify with sufficient precision facts establishing one ormore of the recognised, lower-level grounds which demonstrate that anenrichment is unjust according to law, or in equity. These errors may havestemmed from the false assumption that unjust enrichment is itself a cause ofaction (role 5), as opposed to just a legal principle (role 2) and framework(role 4) for analysing and developing the various subspecies of restitutionary
claim. They have led to a number of claims being struck out.151
Another key problem, which is a product of history, is the tendency of
litigants to plead the elements of the old common law forms of action alongside or instead of the facts that are necessary to make out the relevant restitutionary cause of action. The language of the forms of action sometimes
contains reference to factual elements that are undoubtedly helpful inestablishing a restitutionary cause of action, such as the existence of a request
148

See, eg, Brenner v First Artists’ Management Pty Ltd [1993] 2 VR 221, 260–1 (Byrne J);
Anderson v McPherson [No 2] (2012) 8 ASTLR 321, 350 [203]–[204] (Edelman J) (Supreme
Court of Western Australia).

149

That is to say, a duty within a category that has been recognised in the precedents as giving
rise to gain-based claims. For a case in which the plaintiff sought to plead unjust enrichment
for the wrong of a pure breach of contract, which is not (as yet) recognised as a restitutionary
cause of action in Australian law, see Brambles Holdings Ltd v Bathurst City Council (2001) 53
NSWLR 153.

150

Ancient Order of Foresters (n 78) 923 [7] (Kiefel CJ, Keane and Edelman JJ).

151

See, eg, Coshott v Lenin (2006) 4 DCLR(NSW) 13, 22 [42] (Neilson DCJ), affd [2007]
NSWCA 153 (on other grounds); Chidiac (n 143) [216]–[217] (Ward J) (although the restitutionary claim also failed on other substantive grounds); Alexiadis v Zirpiadis (2013) 302 ALR
148, 154 [29], 155–6 [32]–[34] (Kourakis CJ), 176 [133] (Gray J), 191 [220] (White J) (Supreme Court of South Australia); Gambaro (n 110) [26] (Sofronoff P); Gujarat NRE India Pty
Ltd v Wollongong Coal Ltd (2018) 130 ACSR 133, 178 [270] (Robb J) (Supreme Court of New
South Wales).

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for work in a case in which the plaintiff is seeking remuneration for services
provided. But it is a mistake to think that the old forms of action themselves
constitute, specify or restrict the substantive grounds on which an unjust
enrichment claim can be established. As regards constitution and specification,a ‘quantum meruit’ is not a cause of action in itself, but simply a historicalform of action through which one of several different possible causes of actionin unjust enrichment can be asserted, including, potentially, the fact that thework was provided for a consideration that has failed, or by mistake, or was
freely accepted by the defendant.152 Each of these distinct, substantive
grounds for restitution is likely to require distinct facts to be pleaded.
Nor does the form of the action, with its emphasis upon a request for work,
restrict the possibilities of unjust enrichment claims in respect of such work.
A request is simply one (albeit perhaps the best) way of establishing that thedefendant is enriched by work and that it would be unjust for him or her not
to pay for it. There are alternative ways in which both elements can beestablished. As regards enrichment, for example, a service may be held to beincontrovertibly beneficial where it saves a defendant a necessary expense,153
or, perhaps, because the defendant unconscientiously accepted it.154 As it is,
courts accommodate claims in such cases by ‘inferring’ or ‘implying’ requests
for the work in circumstances in which such facts are alleged and proven.155
This is confusing to all concerned. The fiction of request in such instances
resurrects, in yet another form, the old ‘implied contract fallacy’ that has been
resoundingly rejected by modern courts.156
It is scarcely surprising in these circumstances that the proper pleading ofclaims for services remains a stumbling block for plaintiffs. As it is, if no152

Exceptionally, it may also have supported the implication of a genuine agreement to pay froma request, but the cause of action then lies in contract, not in unjust enrichment law. Pavey(n 2) stands firmly against strained or fictional implications of this type.

153

See, eg, Monks v Poynice Pty Ltd (1987) 8 NSWLR 662, 664 (Young J).

154

On the continuing role of free acceptance even after Lumbers, see Lampson (n 41) [79]–[85](Edelman J).

155

The circumstances in which requests for benefits have been historically ‘inferred’ in this way
are described by Young AJA in Progressive Pod Properties Pty Ltd v A & M Green Investments
Pty Ltd [2012] NSWCA 225. They include cases: where a surety discharges a debtor’s debt;
where a payment is made under legal compulsion; where payments are made on behalf ofanother in accordance with the rules of an enterprise of which both parties are aware; andwhere a reasonable person would expect to pay for the benefit unless they reject it within areasonable time: at [56]–[58]. His Honour emphasises that the list of cases is not exhaustive:at [57].

156

See, eg, Pavey (n 2) 227 (Mason and Wilson JJ); Westpac (n 55) 673 (Mason CJ, Wilson,
Deane, Toohey and Gaudron JJ); Baltic Shipping (n 58) 356–7 (Mason CJ).

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Unjust Enrichment in Australia: What Is(n’t) It?

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express request was made for work provided, they are formally required toplead facts which establish a basis for ‘inferring’ one, such as the defendant’s
acceptance of the work, its necessity, or its incontrovertibly beneficial nature.
The confusion of historical forms and writs with modern causes of action has
also sometimes led plaintiffs to claim a ‘quantum meruit’ in respect of work in
the alternative to alleging a cause of action in unjust enrichment, when thequantum meruit sought is actually based upon a defendant’s unjust
enrichment.157
All of this suggests that the transparency and efficiency of pleading practices in respect of restitutionary causes of action is still being seriously
impacted by historical and procedural forms that should long ago have beenabandoned, as well as by the uncertainty (to which this article has pointed)
about the nature of the relevant ‘causes of action’ in unjust enrichment law.
Whilst we try to rectify these deficiencies with celerity, the key practicalpriority for pleaders, I suggest, is to be sure to allege all the facts necessary tomeet the substantive requirements of the various restitutionary causes ofaction falling within the unjust enrichment category, not simply the historicalrequirements of form, because the old forms are likely to prove deceptive as
well, potentially, as unduly restrictive in the light of the developing law.
IV C O N C LU S I O N
Commonly, all that lies between alliance and antagonism is a misunderstanding. The main thesis of this article has been that a failure properly to distinguish between the different roles that the idea of unjust enrichment can playin legal reasoning underlies much of the confusion and suspicion that hascome to be expressed about it in recent times. If we draw upon all theevidence, there is good authority for the proposition that the idea of unjust
enrichment in Australia plays the second, third and fourth roles identified inPart II above. In the post-Hills era, it therefore constitutes a category of law(albeit one the outer edges of which are still being fully defined). It operates asa legal principle in that category, which assists in understanding and developing the various restitutionary causes of action it contains, and it increasingly
provides an analytical framework that can assist in understanding and157

See, eg, Peet Ltd v Richmond [2009] VSC 130, where the plaintiff ’s quantum meruit claim wasoriginally quantified by reference to the value of the work done and the unjust enrichment
claim by reference to the profit the defendant obtained as a result of it: at [11](Hollingworth J). The latter claim was dropped on appeal: Peet Ltd v Richmond (2011) VR
465, 466.

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structuring the various elements of different restitutionary claims. The idea is
not a purely moral principle lying in the personal, ethical intuitions or
discretion of a judge, nor, crucially, does it describe a singular cause of actionin the dispositive, concrete sense to which I have referred.
Separating these roles from one another, and thereby distinguishing between that which unjust is and that which it is not, ought, I have argued, togive courts greater confidence in using the idea in the future. It can also
improve our pleading practices. Equally importantly, perhaps, it can bringgreater transparency and dignity to modern debate by revealing the extent towhich supporters and critics of the idea, all of whom are spiritual allies in thecause of restitutionary justice, have hitherto been talking at cross-purposes to
one another.

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