¹ [2011] UKSC 10.

² Para. [167].

³ So far as the conceptual element goes, English law is here in accord with all other European legal systems: R. Zimmermann, “Conditio sine qua non: Comparative Report”, in B.Winiger/B.A. Koch/H. Koziol/R. Zimmermann (eds.), Digest of European Tort Law, vol.1: Essential Cases on Natural Causation (Vienna 2007), § 1/29, no.1

⁴ Different reasoning underlies this recognition, which is largely an academic consensus. One move is simply to have a special rule in such cases without conceptual elaboration: e.g. Art. 3:102, Principles of European Tort Law; Restatement Third (Torts), §27; another is to argue that but-for (a test of simple necessity) is not all there is to the concept of causation (which is a complex of necessity and sufficiency): e.g. Wright, R.W., “Causation in Tort Law” (1985) 73 California Law Review 1735CrossRefGoogle Scholar.

⁵ United States: Summers v. Tice 33 Cal. 2d 80; 199 P. 2d 1 (1948); see now Restatement Third (Torts), §28(b). Canada: Cook v. Lewis [1951] S.C.R. 830. French and German law also find liability in such cases, though by different routes: C. Van Dam, European Tort Law (Oxford 2006), pp. 286–288.

⁶ (1866) 5 M. 214, 216 (Lord Justice-Clerk), 223–224, 227–229 (Lord Cowan), 232–233 (Lord Benholme), 234–237 (Lord Neave).

⁷ Countess Dowager of Seafield v. Kemp (1899) 1 F. 402, 406 n.3; Fleming v. Gemmill 1908 S.C. 340, 347, 350; Brownlie & Son v. Magistrates of Barrhead 1923 S.C. 915, 927, 933, 935. The idea of contribution to an injury is commonly found in cases of contributory negligence, though these cases are different since but-for causation would not normally have applied to them: Senior v. Ward (1859) 1 El. & El. 385; S.S. “Rowan” v. S.S. “West Carnak” 1923 S.C. 316, 338. Note too the use of the idea by the Scottish Lord Watson in Wakelin v. London & South Western Railway Co. (1886) 12 App. Cas. 41, 47.

⁸ H.L.A. Hart and A.M. Honore, Causation in the Law (Oxford 1959), p. 211.

⁹ 1955 S.C. 320; [1956] A.C. 613.

¹⁰ Deakin, Simon, “Evolution for Our Time: A Theory of Legal Memetics” [2002] Current Legal Problems 1CrossRefGoogle Scholar.

¹¹ See in particular the summary of Lord Reid, [1956] A.C. 613, 621.

¹² So far as one can judge from case notes, contemporaries did not see it as marking any major breach with orthodoxy: (1956) 72 L.Q.R. 306; (1956) 19 M.L.R. 530 (C. Grunfeld); (1956) 1 Jurist (N.S.) 177 (DM Walker). Cf. Duke of Buccleuch v. Cowan, above.

¹³ Holtby v. Brigham & Cown (Hull) Ltd [2000] 3 All E.R. 421 (according to the relative lengths of the exposure of each wrongdoer). Cf. M. Jones in M. Jones (ed.), Clerk & Lindsell on Torts, 20^th edn. (London 2010), 2–29.

¹⁴ For this interpretation, see: Bailey, S.H., “Causation in Negligence: What is a Material Contribution?” (2010) 30 Legal Studies 167CrossRefGoogle Scholar. It should be noted that this is analytically different from saying that the defendant was liable because he made the extent of the disease worse, in the sense of making its physical effects worse than they would have been.

¹⁵ For a model of this notion of contribution, see Stapleton, Jane, “Choosing what we mean by ‘Causation’ in the Law” (2008) 73 Missouri Law Review 433Google Scholar.

¹⁶ 1972 S.L.T. (Notes) 61; 1973 S.C. (H.L.) 37; [1973] 1 W.L.R. 1. Before this Wardlaw v. Bonningtons Castings had been followed in Nicholson v. Atlas Steel Foundry and Engineering Co. Ltd. [1957] 1 W.L.R. 613 (H.L.), another – Scottish – case of pneumoconiosis.

¹⁷ Below, ***

¹⁸ 1973 S.C. (H.L.) 37, 45, per Lord President Clyde.

¹⁹ “James McGhee: A Second Mrs. Donoghue?” [2003] C.L.J. 587, 592–595, 599, 600–612.

²⁰ So too Gardiner v. Motherwell Machinery & Scrap Co Ltd [1961] 1 W.L.R. 1424.

²¹ [1987] Q.B. 730.

²² [1987] A.C. 750.

²³ Fairchild v. Glenhaven Funeral Services Ltd [2003] 1 A.C. 32.

²⁴ Background exposure was (without warrant) ignored: see Stapleton, J.,“Lords a'leaping evidentiary gaps” (2002) 10 Torts Law Journal 276, 281Google Scholar.

²⁵ It may be noted here that German law (even if it does not arguably cover the precise facts of Fairchild for other reasons) restricts its exception to proof of causation, § 830(2) BGB, to cases where there is a demonstrated right to damages (festehende Ersatzberechtigung): G. Wagner, in F.J. Säcker, R.Rixecker (eds.), Münchener Kommentar zum BGB §§705-853, 2282, §39.

²⁶ Paras. [65], [67] (Lord Bingham), [108] (Lord Hoffmann).

²⁷ The transition is explicit at [13]–[14].

²⁸ [2006] 2 A.C. 572.

²⁹ As Lord Clarke, at para. [55], and Smith L.J. at paras. [18] and [27] stated in the Court of Appeal in Sienkiewicz [2009] EWCA Civ 1159. Criticised by Steel, S., “Uncertainty over Causal Uncertainty: Sienkiewicz v Greif” (2010) 73 Modern Law Review 646, 652–653Google Scholar

³⁰ Compensation Act 2006, s.3

³¹ This follows from the fact that the Court accepted what was slightly blurred by Smith L.J. in the Court of Appeal that s.3 of the Compensation Act 2006 is entirely parasitic upon there being liability already established by common law (see Sienkiewicz, para. [70] per Lord Phillips; para. [131] per Lord Rodger; para. [223] per Lord Dyson) and the fact that the common law exception is not limited to mesothelioma cases (McGhee itself being the obvious non-mesothelioma case).

³² [2008] EWCA Civ 883. Noted by M. Stauch [2009] C.L.J 27.

³³ Ibid., para. [46].

³⁴ Above, ***.

³⁵ This interpretation finds its roots in Lord Rodger's speech in Fairchild, para. [129]. It was adopted by the Court of Appeal in Ministry of Defence v. AB & Ors [2010] EWCA Civ 1317 [134]. It also seems to be accepted by the judge obiter in Ingram v Williams [2010] EWHC 758 (QB), para. [83].

³⁶ Fairchild, para. [2] per Lord Bingham, paras. [47] and [61] per Lord Hoffmann; Barker para. [17] per Lord Hoffmann, para. [53] per Lord Scott, para. [109] per Lord Walker.

³⁷ For a similar observation, see Wright, R.W., “Liability for Possible Wrongs: Causation, Statistical Probability, and the Burden of Proof” (2009) 41 Loyola of Los Angeles Law Review 1295, 1296Google Scholar.

³⁸ Nor is this a fiction – or, at least, no more so than the balance of probabilities rule.

³⁹ Barker, para. [35].

⁴⁰ Para. 17.

⁴¹ Paras. [120]–[122].

⁴² See also, D. Nolan, “Causation and the Goals of Tort Law”, in A. Robertson and Tang Hang Wu (eds.) The Goals of Private Law (Oxford 2009), 165, 177–178.

⁴³ This is how such liability is characterised in Austrian law, building on the theory of F. Bydlinski, “Haftung bei alternativer Kausalität”, [1959] Juristische Blätter 1. See K. Oliphant, “Alternative Causation: A Comparative Analysis of Austrian and English Law”, in P. Apathy/R. Bellenberger/P. Bydlinski/G. Iro/ E. Karner/M. Karollus (eds.), Festschrift für Helmut Koziol (Vienna 2010), 795, 798.

⁴⁴ The probability of causation for the environment is given by 1 – ((28.39–24)/28.39). For a discussion of this calculation (normally known as the “attributable fraction”) see, Scheines, R., “Causation, Truth and the Law” (2007–2008) 73 Brooklyn Law Review, 959, 969Google Scholar.

⁴⁵ Lady Hale thought that discussion of the validity of the statistical evidence presented was “obiter”: para. [169]. On the other hand, she expresses agreement with Lord Rodger, whose approach does not make this issue obiter, that holding the defendant liable was a “logical consequence” of Fairchild: para. [167]. Lord Brown agreed that the state of the law is as described by Lords Rodger and Phillips (para. [174]) but his reasons seem to be closer to the risk argument described in the text: see para. [184].

⁴⁶ Sienkiewicz, para. [213].

⁴⁷ Ibid. paras. [45], [52].

⁴⁸ See also Lord Rodger para. [135].

⁴⁹ Paras. [96]–[97]; [101]–[102].

⁵⁰ Paras. [98]–[99].

⁵¹ Para. [96]; taken from Lord Mackay's speech in Hotson, and originally from Herskovits v. Group Health Cooperative of Puget Sound (1983) 664 P 2d 474 (Supreme Court of Washington), per Brachtenbach J. (in dissent). Similar examples have been endlessly discussed in the literature. For a useful (if partisan) introduction, see A. Stein, Foundations of Evidence Law (Oxford 2005), chapter 3, pp. 238–240.

⁵² Para. [101].

⁵³ Para. [102]. Stapleton, J., “Factual Causation and Asbestos Cancers” (2010) 126 L.Q.R. 351Google Scholar, 354 supported this analysis.

⁵⁴ Paras. [91], [93].

⁵⁵ Para. [91].

⁵⁶ Beginning at para. [143]; see especially paras. [153] and [156].

⁵⁷ His Lordship acknowledged his debt to Gold's, Steve article, “Causation in Toxic Torts: Burdens of Proof, Standards of Persuasion and Statistical Evidence” (1986–7) 96 Yale Law Journal 376CrossRefGoogle Scholar, whose analysis distinguishes between fact and belief probability, at pp. 380–384.

⁵⁸ All else would not be equal, for example, if the particular person had been exposed to other risk sources for dermatitis.

⁵⁹ Para. [203].

⁶⁰ Para. [189].

⁶¹ Para. [220].

⁶² Para. [174].

⁶³ Para. [222].

⁶⁴ Except Lord Brown who did not discuss the point at all.

⁶⁵ No one, however, doubted that epidemiological evidence could be put to valuable use alongside other “specific” evidence to show causation in appropriate cases E.g. [163] per Lord Rodger. That view clearly reflects earlier understandings: see Gregg v Scott [2005] 2 A.C. 176, [32] per Lord Nicholls.

⁶⁶ Though it is indeed a matter of some philosophical dispute: for an overview, see H.L. Ho, A Philosophy of Evidence Law (Oxford 2008), chapter 3, especially pp. 106 ff.

⁶⁷ Sienkiewicz, para. [156] per Lord Rodger.

⁶⁸ Seltsam v. McGuinness [2000] NSWCA 29, [136] per Spiegelman C.J., citing many authorities; Sargent v. Massachusetts Accident Co. (1940) 29 N.E. 2d 825 at 827, cited by R.W.Wright, “Proving Causation: Probability versus Belief”, in R. Goldberg (ed.), Perspectives on Causation (forthcoming Oxford 2011), 13. For Canadian cases, see L. Khoury, Uncertain Causation in Medical Liability (Oxford 2006), 34–35.

⁶⁹ There had been some suggestion that this was the position in England pre-Sienkiewicz: see Gregg, paras. [28]–[29] per Lord Nicholls. Lord Mackay's speech in Hotson is equivocal; clearer is Croom-Johnson L.J. in the Court of Appeal, [1987] A.C. 750, 769. The Australian cases leave this issue open: Seltsam, at paras. [78]–[79], [89]; Amaca Pty. Ltd v. Ellis [2010] HCA 5, [62]; for some discussion, see Hamer, D., “Before the High Court: Mind the Evidential Gap: Causation and Proof in Amaca Pty Ltd v Ellis”, (2009) 31 Sydney Law Review 465, 466Google Scholar.

⁷⁰ See Gold, S., “The More We Know, The Less Intelligent We Are? – How Genomic Information Should and Should Not, Change Toxic Tort Doctrine” (2010) 34 Harvard Environmental Law Review 369, 381Google Scholar. Of course, it could be disputed whether these courts are in fact applying a “special rule”, without actually affirming that such evidence amounts to proof on the balance of probabilities as traditionally understood.

⁷¹ (2000) 54 B.M.L.R. 100

⁷² Ibid., 101.

⁷³ Lord Phillips seems to have had situations like this in mind when he observed in Sienkiewicz that the balance of probability standard is “one that is inherently capable of producing capricious results” Sienkiewicz, [26]. Criticised by Wright, “Proving Causation”, p. 44 n. 94.

⁷⁴ Contra R.W. Wright, “Proving Causation”. This is a very difficult question to which we have only been able to give cursory attention here.

⁷⁵ Above, p. 457.

⁷⁶ See e.g. Fairchild, para. [33] per Lord Bingham. It is no accident that Professor Dworkin uses cases of uncertain causation to illustrate his moral theory of law: see Dworkin, R., “Hart's Postscript and the Character of Political Philosophy” (2004) 24 Oxford Journal of Legal Studies 1CrossRefGoogle Scholar.

⁷⁷ Sienkiewicz, para. [58] per Lord Phillips; Lord Mance agreed with this description at para. [184]. See also Lady Hale at para. [168].

⁷⁸ Though there is no reason within the law as it stands to restrict Barker to employers.

⁷⁹ The single-agent limitation will not preclude its application in a case like Hotson.

⁸⁰ Cf. Khoury, L., “Causation and Risk in the Highest Courts of Canada, England and France” (2008) 124 L.Q.R. 103Google Scholar, 127. Furthermore, the traditional rules of evidence – all or nothing liability on the balance of probabilities – have already been re-written in the context of liability for the loss of an economic chance.

⁸¹ See Morgan, J., ‘Policy Reasoning in Tort Law: The Courts, the Law Commission and the Critics’ (2009) 125 L.Q.R. 215Google Scholar.

⁸² The Principles of European Tort Law opt for proportional liability in all cases. See Art. 3:101; Art. 3:106.

⁸³ See e.g. E. Weinrib, The Idea of Private Law (Cambridge, Mass. 1995), 153.

⁸⁴ See R. Stevens Torts and Rights (Oxford 2006) 150–151.

⁸⁵ As in Sindell v Abbott Laboratories 26 Cal. 3d. 588; 607 P. 2d. 924 (1980).