1 It is notable that the two Gedenkschriften that have been published in his memory both have titles reflecting his contributions to legal classification: Burrows, A and Lord Rodger of Earlsferry (eds) Mapping the Law: Essays in Memory of Peter Birks (Oxford: Oxford University Press, 2006)CrossRefGoogle Scholar and Ricketts, C and Grantham, R (eds) Structure and Justification in Private Law: Essays for Peter Birks (Oxford: Hart Publishing, 2008).Google Scholar

2 P Birks ‘Equity in the modern law: an exercise in taxonomy’ (1996) 26 UWALR 1 at 9.

3 Birks, P and McLeod, G Justinian's Institutes (London: Butterworths, 1987) discusses the original taxonomy at pp 12–26.Google Scholar

4 Samuel, G ‘Can Gaius really be compared to Darwin?’ (2000) 49 ICLQ 297,CrossRefGoogle Scholar H Dagan ‘Legal realism and the taxonomy of private law’ in Ricketts and Grantham, above n 1.

5 Birks, above n 2, at 7.

6 Ibid, at 7.

7 Birks, P ‘Preface’ in Birks, P (ed) English Private Law – Volume I (Oxford: Oxford University Press, 2000) p xli.Google Scholar

8 Ibid, p xxix.

9 Ibid, p xxxv.

10 Viner, C A General Abridgment of Law and Equity: Alphabetically Digested Under Proper Titles, with Notes and References to the Whole (London: Aldershot, 1742–1753).Google Scholar

11 Halsbury's Laws of England (London: Butterworths, 4th edn, 1973).Google Scholar

12 Stevens, R Torts and Rights (Oxford: Oxford University Press, 2007) p 287:CrossRefGoogle Scholar ‘An events-based classification is extremely useful for demonstrating the independence of the law of unjust enrichment. For other purposes, it is less helpful’.

13 Ibid, pp 287–288.

14 Birks, above n 2, at 10. Primary rights (eg rights to contractual performance or bodily integrity) are sometimes protected directly (eg by way of specific performance or injunction). Often, however, they are protected by way of secondary rights (eg to damages) that arise when the primary rights are themselves breached.

15 Birks, P ‘Definition and division: a meditation on Institutes 3.13’ in Birks, P (ed) The Classification of Obligations (Oxford: Oxford University Press, 1997) p 1 at p 21.Google Scholar

16 Sinclair v Brougham [1914] AC 398 at 415 per Lord Haldane LC.

17 Witness the similar formulations in Robinson v Harman (1848) 1 Exch 850 at 855 per Parke B and Livingstone v Rawyards Coal Co (1880) 5 App Cas 25 at 39 per Lord Blackburn, a similarity not always drawn in either contract or torts texts but often drawn in texts on remedies. See, eg, Burrows, A Remedies for Torts and Breach of Contract (Oxford: Oxford University Press, 3rd edn, 2004) pp 33–34.Google Scholar

18 Cf The Heron II [1969] 1 AC 350.

19 Mayr, E and Ashlock, PD Principles of Systematic Zoology (New York: McGraw-Hill, 2nd edn, 1991) p 126.Google Scholar

20 A taxon, or taxonomic unit, is a name designating an organism or group of organisms. A taxon is assigned a rank and can be placed at a particular level in a systematic hierarchy.

21 Viner, above n 10, p 126.

22 G Samuel ‘English private law: old and new thinking in the taxonomy debate’, above n 4, at 341–342.

23 Ibid, at 339.

24 It is notable that Linnaean classification is giving way to cladistic taxonomy, whereby organisms are classified to reflect the Darwinian principle of common descent.

25 Strictly speaking, the rules on claiming are not exclusively equitable. However, the great majority of cases do fall on the equitable side of the common-law–equity divide.

26 In Westdeutsche Landesbank Girozentrale v Islington LBC [1996] AC 669, the unjust enrichment thesis of resulting trusts was rejected by the House of Lords. In Foskett v McKeown [2001] 1 AC 102, the House of Lords likewise rejected the unjust enrichment thesis of claiming traceable proceeds.

27 Royal Brunei Airlines Sdn Bhd v Tan [1995] 2 AC 378 at 382 per Lord Nicholls of Birkenhead, Twinsectra Ltd v Yardley [2002] 2 AC 164 at 194 per Lord Millett, Dubai Aluminium Co Ltd v Salaam [2003] 2 AC 366 at 391 per Lord Millett. Cf Citadel General Assurance Co v Lloyds Bank Canada (1997) 152 DLR (4th) 411, BCCI (Overseas) v Akindele [2001] Ch 437, Farrah Constructions Pty Ltd v Say-Dee Pty Ltd [2007] HCA 22. Cf also the more ambivalent views in Grupo Torras SA v Al-Sabah (No 5) [2001] Lloyd's Rep Bank 36 at 62.

28 Birks, P ‘Restitution and resulting trusts’ in Goldstein, S (ed) Equity and Contemporary Legal Developments (Jerusalem: Harry and Michael Sacher Institute for Legislative Research and Comparative Law, 1992) p 335.Google Scholar

29 The other families were ‘It was shabby of you to receive it’ and ‘There is a good reason for giving it back’.

30 Above n 26.

31 Citing with approval Swadling, WJ ‘a new role for resulting trusts?’ (1996) 16 LS 133.Google Scholar

32 Chambers, R Resulting Trusts (Oxford: Oxford University Press, 1997).CrossRefGoogle Scholar

33 Contra Swadling, W ‘Explaining resulting trusts’ (2008) 124 LQR 72 at 90–94.Google Scholar

34 [1999] 1 WLR 1399 at 1412.

35 Cf Twinsectra Ltd v Yardley, above n 26, at 190 per Lord Millett.

36 Millett, Lord ‘Proprietary restitution’ in Degeling, S and Edelman, J (eds) Equity in Commercial Law (Sydney: Lawbook Co, 2005) p 309 at p 316.Google Scholar

37 The eight major taxonomic ranks are: (i) domain; (ii) kingdom; (iii) phylum/division; (iv) class; (v) order; (vi) family; (vii) genus; and (viii) species.

38 Birks, P ‘Property, unjust enrichment, and tracing’ (2001) 54 CLP 231 at 245.Google Scholar

39 Ibid, at 246, relying on Lipkin Gorman v Karpnale Ltd [1991] 2 AC 548 and Trustee of FC Jones & Sons v Jones [1997] Ch 159. This must be correct for the category of ‘wrongs’ presupposes the existence of a primary right which may be protected by the law of ‘wrongs’ upon infringement.

40 Ibid, at 247. Contra Swadling, W ‘Property’ in Burrows, A (ed) English Private Law (Oxford: Oxford University Press, 2nd edn, 2007) at [4.314] and [4.436.Google Scholar

41 Birks, P ‘Property and unjust enrichment: categorical truths’ 1997 NZLR 623 at 628.Google Scholar

42 Birks, above n 38, at 241.

43 Virgo, G The Principles of the Law of Restitution (Oxford: Oxford University Press, 2nd edn, 2006) pp 11–17.CrossRefGoogle Scholar

44 Grantham, RB and Rickett, Cef ‘Property and unjust enrichment: categorical truths or unnecessary complexity?’ 1997 NZLR 668.Google Scholar

45 It is significant that whereas Virgo speaks of the multicausality of restitution, he does not do so in respect of causative events.

46 Above n 43, p 15.

47 Above n 44, at 671.

48 Ibid, p 677.

49 [2001] 1 AC 102.

50 Lord Millett, above n 36, p 314.

51 Ibid, p 314.

52 His Lordship's explanation of the basis of the rule does not actually support the rule. According to Lord Millet, ibid, p 315, a beneficiary is able to claim the traceable product of the trust property because, although they were permitted to falsify the accounts provided by the trustee should there be an unauthorised disposition, they were not obliged to do so. In choosing to let the account stand, they claimed the traceable product of the unauthorised disposition. However, if such an account of the development of claiming is correct, then claiming should be dependent on the existence of a duty to account, which perhaps explains the historical requirement in equity that a fiduciary relationship be established before a party could trace into substitutes and claim the substitutes.

53 Swadling, above n 40, paras [4.314] and [4.436].

54 For an introduction to contract theory, see, eg, SA Smith Contract Theory (Oxford: Clarendon Press, 2004).

55 Stevens, above n 12, pp 9–14.

56 Birks, P ‘The concept of a civil wrong’ in Owen, DG (ed) Philosophical Foundations of Tort Law (Oxford: Oxford University Press, 1995) p 29 at pp 42–45.Google Scholar

57 For example, breach of contract.

58 There remains much controversy over the normative justifications of unjust enrichment liability; see, eg, Smith, L ‘Restitution: the heart of corrective justice’ (2001) 79 Tex L Rev 2115,Google Scholar E Weinrib ‘The normative structure of unjust enrichment’ in Rickett and Grantham, above n 1, p 21, Dagan, above n 4, p 147.

59 Stevens, above n 12, p 285. See also E Sherwin ‘Legal positivism and the taxonomy of private law’ in Rickett and Grantham, above n 1.

60 Birks, P ‘Misdirected funds: restitution from the recipient’ 1989 LMCLQ 296.Google Scholar

61 Lord Nicholls of Birkenhead ‘Knowing receipt: the need for a new landmark’ in Cornish, WR et.al (eds) Restitution, Past, Present and Future (Oxford: Hart Publishing, 1998) p 231. See alsoGoogle Scholar

62 See, generally, Low, Kfk ‘Recipient liability in equity: resisting the siren's lure’ 2008 RLR 96.Google Scholar

63 Holiday v Sigil (1826) 2 C&P 176, Neate v Harding (1851) 6 Exch 349, Clark v Shee and Johnson (1774) 1 Cowp 197.

64 The claim that these cases are founded on unjust enrichment rests upon the employment of money had and received as their form of action. However, it is well established that the form of action tells us very little about the nature of the claim itself: see United Australia Ltd v Barclays Bank Ltd [1941] AC 1 at 18 per Viscount Simon LC. See also D Fox ‘Legal title as a ground of restitutionary liability’ [2000] RLR 465.

65 [1848] Ch 465; affirmed, sub nom Ministry of Health v Simpson [1951] AC 251.

66 Commissioner of Stamp Duties (Queensland) v Livingston [1965] AC 694.

67 [1991] 2 AC 548.

68 Virgo, G ‘Reconstructing the law of restitution’ (1996) 10 TLI 20 Google Scholar;

69 Low, above n 62, at 100–102.

70 Birks, above n 60, at 306.

71 Low, above n 62, at 100–102.

72 The resort to ‘gift’ is unconvincing as the ‘explanation’ is conclusory rather than explanatory; see Watts, P ‘Book review: Unjust Enrichment’ (2005) 121 LQR 163 at 166.Google Scholar

73 Low, above n 62, at 102–103.

74 Ibid, at 103–105.

75 Though not all expository classifications have this capacity. An alphabetical classification is almost useless in this respect.

76 The miscellany is too diverse to be helpful in itself and the category of ‘wrongs’, being premised upon a breach of a right, is derivative and therefore unhelpful in locating normative justifications.

77 Peden, E ‘Policy concerns behind implication of terms in law’ (2001) 117 LQR 459.Google Scholar

78 Under s 14(2) of the Sale of Goods Act 1979.

79 Which exclusion may not be operative under s 6 of the Unfair Contract Terms Act 1977. Certainly, even if a broader view of consent is taken, the ‘consent’ that triggers the seller's obligation to transfer the subject of the sale is very different than the ‘consent’ that triggers his obligation to ensure that it is of satisfactory quality. At the very least, therefore, there are two sub-categories of ‘consent’ at work in the law of primary contractual obligations.

80 Birks, P Unjust Enrichment (Oxford: Clarendon Press, 2nd edn, 2005) p 126. See alsoCrossRefGoogle Scholar

81 Smith, L ‘Unjust enrichment: big or small?’ in Degeling, S and Edelman, J (eds) Unjust Enrichment in Commercial Law (Sydney: Lawbook Co, 2008) p 35. See alsoGoogle Scholar

82 Smith, ibid, pp 40–43.

83 For example, a contractual right must be supported by consideration, and a gift of a chattel must be effected either by deed or by delivery.

84 The logic in this argument is not derived from the taxonomy itself. Rather, it would be distinctly odd to suggest, for example, that a promise to pay $X should result in an obligation to pay $Y on the basis of the promise, where Y > X. Exceptionally, of course, the law will imply terms into a contract by law which do not map from the parties' intentions, though this arguably stems not from ‘consent’ but from ‘other events’.

85 Smith, above n 81, pp 43–45.

86 Contra Swadling, W ‘Rescission, property and the common law’ (2005) 121 LQR 123. But seeGoogle Scholar

87 Car and Universal Finance Co Ltd v Caldwell [1965] 1 QB 525.

88 Branston, CA ‘the forcible recaption of chattels’ (1912) 28 LQR 262.Google Scholar

89 Cf Billson v Residential Apartments Ltd [1992] AC 494.

90 Cf Hedley, S A Critical Introduction to Restitution (London: Butterworths, 2001)Google Scholar, Hedley, S Restitution: Its Division and Ordering (London: Sweet & Maxwell, 2001).Google Scholar

91 Barclays Bank Ltd v WJ Simms Son and Cooke (Southern) Ltd [1980] QB 677, Lloyds Bank plc v Independent Insurance Co Ltd [1999] 2 WLR 986, Kleinwort Benson Ltd v Lincoln City Council [1999] 2 AC 349.

92 Smith v Hughes (1871) LR 6 QB 597.

93 Dextra Bank and Trust Co v Bank of Jamaica [2002] 1 All ER (Comm) 193, Commerzbank AG v Price-Jones [2005] Lloyd's Rep 298.

94 Dextra Bank, ibid, at [38] (emphasis added).

95 For which, see Stevens, above n 12, pp 303–304.

96 There are useful similarities to the law of ‘wrongs’ even though specific rules may differ. Thus, it seems clear that the law does not permit recovery of all losses sustained by a breach of a primary right, however important that right may be though the specific limits may differ from one claim to another. Thus, where a claim is made in deceit, all losses directly caused are recoverable whereas only losses that are not too remote are recoverable for claims in negligence and for breach of contract, with further distinctions between the two.