Drafts of this paper were presented at the ‘Contract and Promise’ workshop at Georgetown University, and at a staff seminar at UCL. Thank you to participants and colleagues in those sessions for many helpful comments. For pressing me on various issues thanks in particular to Robert Chambers, Andrew Gold, Jody Kraus, Stuart Lakin, George Letsas, James Penner, Stephen Smith, Robert Stevens and the two referees from this journal. Special thanks also to the student editor from this journal, Tim Duncan, whose suggestions have helped me to markedly sharpen up the arguments. The usual caveat applies.

1. Birks, Peter, Unjust Enrichment, 2nd ed. (Oxford: Oxford University Press, 2005)CrossRefGoogle Scholar [Birks, Unjust Enrichment].

2. Weinrib, Ernest J., The Idea of Private Law (Cambridge, MA: Harvard University Press, 1995)Google Scholar [Weinrib, Idea].

3. Weinrib, Ernest J., “The Normative Structure of Unjust Enrichment” in Rickett, Charles & Grantham, Ross, eds., Structure and Justification in Private Law: Essays for Peter Birk (Oxford: Hart, 2008) 21 Google Scholar [Weinrib, “Normative Structure”]; Weinrib, Ernest J., “Correctively Unjust Enrichment” in Chambers, Robert, Mitchell, Charles & Penner, James, eds., Philosophical Foundations of the Law of Unjust Enrichment (Oxford: Oxford University Press, 2009) 31 CrossRefGoogle Scholar [Weinrib, “Correctively Unjust”].

4. Here I paraphrase what Joseph Raz had to say about the limits of Hans Kelsen’s theory of law: Its failure, Raz said, was “illuminating” and shed “light on the intricacies of the problems involved and on their possible solutions.” The Authority of Law: Essays on Law and Morality (Oxford: Oxford University Press, 1979) at 122 Google Scholar.

5. Weinrib, Idea, supra note 2 at 114.

6. Ibid. at 115.

7. See text accompanying notes 24-27 and 30-33, below.

8. Weinrib, Idea, supra note 2 at 134.

9. Ibid. at 136.

10. Ibid. at 141.

11. Ibid. at 178-79.

12. Ibid. at 144.

13. Ibid. at 139.

14. Ibid. at 13,19.

15. The point was made by John Gardner in his review of Weinrib, Idea: see “The Purity and Priority of Private Law” (1996) 46 U.T.L.J. 459 at 474. See also Perry, Stephen R., “The Moral Foundations of Tort Law” (1992) 77 Iowa L. Rev. 449 at 479-80Google Scholar.

16. Gardner, John, “What is Tort Law for? Part 1. The Place of Corrective Justice”Google Scholar forthcoming in Law and Philosophy, draft available online: SSRN http://papers.ssrn.com/s013/papers.cfm?abstract_id=1538342 1 at 11. Accessed 30 June 2010 [Gardner, “Tort Law”].

17. Ibid.

18. Ripstein, Arthur, “As if it Had Never Happened” (2006-2007) 48 William & Mary L. Rev. 1957 at 1967Google Scholar [Ripstein, “Had Never Happened”].

19. Ibid. at 1969.

20. Ibid. at 1968. Cf. Stewart, Hamish, “A Formal Approach to Contractual Duress” (1997) 47 U.T.L.J. 175 at 190,195CrossRefGoogle Scholar. Stewart explains rights to rescind for duress in contract law on the basis of the role they play in upholding the promisor’s capacity to set and pursue her own ends.

21. See Ripstein, “Had Never Happened”, ibid. at 1972, 1981-1983.

22. One could reply that if that is the case, then it means that Kantian rights, because they generate no remedial duties when they are violated, are simply not rights. The claim is that a right cannot be a right if it is completely ineffective. I take no position on this issue, and assume instead for the sake of argument that Kantian rights are rights even though they cannot generate remedial duties. Of course, if that assumption is wrong then that is a further problem for Kantian right.

23. Although in a recent article, John Gardner claims that Weinrib had the seeds to an answer to this objection. Gardner argues, however, that had they been cultivated, they would have fundamentally compromised Weinrib’s conception of corrective justice: Gardner, “Tort Law,” supra note 16 at 57-60.

24. I put aside the fact that some restitution lawyers would say that there are some cases of restitution not based on wrongdoing that are not unjust enrichment cases, for example, a promise to make restitution of a loan. The distinction is not important for the purposes of my argument.

25. Weinrib, Idea, supra note 2 at 140.

26. Ibid. at 140-41. See also 197-98.

27. The same mistake is made by those who offer property-based accounts of unjust enrichment. For a recent example of this kind of theory see Botterell, Andrew, “Property, Corrective Justice, and the Nature of the Cause of Action in Unjust Enrichment” (2007) 20 Can. J. L. & Jur. 275 Google Scholar. They claim that remedies for unjust enrichment respond to the fact that due to a defective or non-voluntary transfer of an asset by the claimant to the defendant, the defendant wrongfully interferes with the claimant’s property. However, the fact that there is such interference is not sufficient to explain why there should be a remedy for that violation of the claimant’s right.

28. Weinrib, Idea, supra note 2 at 119.

29. Ibid. at 13, 19.

30. Ibid. at 136. As I have already said, it is a fundamental flaw in Weinrib’s project that even with wrongdoing he cannot explain why there should be a remedy, but putting that worry aside, I assume here for the purposes of argument that wrongdoing can explain why there should be a remedy.

31. Ibid. at 141 [emphasis added].

32. McInnes, Mitchell, “Unjust Enrichment: A Reply to Professor Weinrib” [2001] R.L.R. 29 at 43Google Scholar (I have slightly varied the actual example McInnes uses).

33. Weinrib, Idea, supra note 2 at 114.

34. Or, in Dennis Klimchuk’s words, corrective justice purports not merely to “identify a distinctive structure that a legal claim can take,” but to justify “that legal claim taking that structure.” “The Normative Foundations of Unjust Enrichment” in Chambers, Mitchell & Penner, supra note 3, 81 at 87 [Klimchuk, “Normative Foundations”].

35. Birks, Unjust Enrichment, supra note 1 at 6, 9.

36. The Principles of the Law of Restitution, 2nd ed. (Oxford: Oxford University Press, 2006) at 37 CrossRefGoogle Scholar. See also Burrows, Andrew, The Law of Restitution, 2nd ed. (London: Butterworths, 2002) at 25—31 Google Scholar; Jones, Gareth, Goff and Jones: The Law of Restitution, 7th ed. (London: Sweet & Maxwell, 2009) at para. 1—050 Google Scholar.

37. See text accompanying notes 45-47, below.

38. Saprai, Prince, “Restitution Without Corrective Justice” [2006] R.L.R. 41 at 47Google Scholar [Saprai, “Corrective Justice”]. Weinrib now acknowledges the force of this kind of criticism: see Weinrib, “Correctively Unjust,” supra note 3 at 32.

39. See Prince Saprai, “Unconscionable Enrichment?” in Chambers, Mitchell & Penner, supra note 3 at 417. For Feinberg, Joel’s comment, see Harmless Wrongdoing: The Moral Limits of the Criminal Law (Oxford: Oxford University Press, 1988) at 196, 198, 210Google Scholar.

40. Weinrib, Idea, supra note 2 at 10.

41. Ibid. at 9.

42. Weinrib, “Normative Structure,” supra note 3. Weinrib, “Correctively Unjust,” supra note 3.

43. Birks, Unjust Enrichment, supra note 1.

44. One of the articles appears in a book of essays for Peter Birks called Structure and Justification in Private Law. The title echoes the choice that I claim Weinrib needed to make, as indeed does the title of the article itself: “The Normative Structure of Unjust Enrichment”. Both juxtapose the clash between explanation and justification.

45. Weinrib, “Normative Structure,” supra note 3 at 21-22.

46. Ibid. at 23.

47. Ibid. at 24.

48. Ibid. quoting Birks, Peter, An Introduction to the Law of Restitution (Oxford: Clarendon Press, 1985) at 19 Google Scholar [Birks, Introduction].

49. Weinrib, “Normative Structure,” supra note 3 at 25.

50. Ibid. at 26. It is unclear but these seem to map the ‘Birksian’ elements endorsed by Weinrib earlier.

51. Weinrib, “Correctively Unjust,” supra note 3 at 34.

52. Weinrib, “Normative Structure,” supra note 3 at 28; Weinrib, “Correctively Unjust,” ibid. at 36.

53. Weinrib, “Normative Structure,” ibid.; Weinrib, “Correctively Unjust,” ibid. at 36-37.

54. See text accompanying notes 4-24, above.

55. Weinrib, “Normative Structure,” supra note 3 at 29.

56. See Saprai, Prince, “Against Equality of Exchange” (2010) 21 (1) King’s L.J. 71 Google Scholar. Moreover, it does not explain why when there is a defective transfer of wealth the law of property lets title pass. If the law is suspicious of gratuitous transfers it should not let property pass until it is sure that a transfer is fully intended. If it did this, then the role of unjust enrichment as a corrective instrument would be unnecessary. See Nadler, Jennifer, “What Right Does Unjust Enrichment Law Protect” (2008) 28 Oxford J. Legal Stud. 245 at 259-60CrossRefGoogle Scholar.

57. Peter Birks seemed to agree with Weinrib that the purpose of unjust enrichment is to protect selfinterested behavior: “From the time of Lord Nottingham if not before, the value which served as equity’s guiding light, was legal certainty. The court’s principal concern was to keep wealth safe through all the vicissitudes of public and private life.” (1999) 23 Melbourne U.L. Rev. 1 at 22Google Scholar. However, Birks’ claim is, unlike Weinrib’s, purely descriptive or legal. It is not also a normative claim about what the law should do.

58. See Finnis, John, Natural Law and Natural Rights (Oxford: Clarendon Press, 1980) at 36—42 Google Scholar.

59. See, e.g., Nozick, Robert Anarchy, State, and Utopia (Oxford: Blackwell, 1974)Google Scholar.

60. The “something else” includes morally instrumental ends such as, for example, economic efficiency, but also includes morally non-instrumental ends, such as achieving fairness. Weinrib, Idea, supra note 2 at 49-50, 52-53, 55.

61. Ripstein, “Had Never Happened,” supra note 18 at 1969.

62. Weinrib, “Correctively Unjust,” supra note 3 at 41-42.

63. Weinrib, “Normative Structure,” supra note 3 at 30.

64. Ibid. at 35.

65. Ibid.

66. Weinrib, “Correctively Unjust,” supra note 3 at 42: “To vindicate justice in transfer, the law must apply it equally to both parties.”

67. Ibid. at 42.

68. Weinrib, “Normative Structure,” supra note 3 at 36-37.

69. Weinrib, “Correctively Unjust,” supra note 3 at 42.

70. Weinrib, “Normative Structure,” supra note 3 at 37; Weinrib, “Correctively Unjust,” ibid. at 42-43.

71. Weinrib, “Correctively Unjust,” ibid. at 44.

72. Weinrib, “Normative Structure,” supra note 3 at 37; Birks, Introduction, supra note 48 at 265.

73. Weinrib, “Normative Structure,” ibid. at 37.

74. Ibid. at 38.

75. Weinrib, “Correctively Unjust,” supra note 3 at 43.

76. See text accompanying notes 34-38, above.

77. See Klimchuk, “Normative Foundations,” supra note 34 at 90.

78. Weinrib, “Normative Structure,” supra note 3 at 37-38.

79. Klimchuk, “Normative Foundations,” supra note 34 at 91.

80. Weinrib is clear on this point: “Except when the enrichment was intended and accepted as a gift, the defendant can be regarded as assuming that no benefit is given gratuitously, even if the defendant has not turned his mind to this issue.” Weinrib, “Correctively Unjust,” supra note 3 at 43.

81. Ibid.

82. Birks, Unjust Enrichment, supra note 1 at 6; Birks, Peter, “Failure of Consideration and its Place on the Map” (2002) 2 O.U.C.L.J 1 at 8-9Google Scholar. Weinrib says that there is an “obvious normative link” between the parties in a case of unjust enrichment. Weinrib, “Correctively Unjust,” supra note 3 at 53.

83. Weinrib, “Correctively Unjust,” ibid. at 52.

84. See Saprai, “Corrective Justice,” supra note 38 at 46. Cf. Klimchuk, “Normative Foundations,” supra note 34 at 92-93, 98.

85. See Klimchuk, “Normative Foundations,” ibid. at 89.

86. Taylor v. Laird (1856), 25 L.J. Ex. 329 at 332Google Scholar. Cited by Weinrib, “Normative Structure,” supra note 3 at 38.

87. Weinrib, “Normative Structure,” ibid. at 35, citing LJ, Bowen in Falcke v. Scottish Imperial Insurance Co. (1886), 34 Ch. D. 234 (C.A.)Google Scholar: “Liabilities are not to be forced upon people behind their backs any more that you can confer a benefit upon a man against his will.” Weinrib, “Correctively Unjust,” supra note 3 at 44.