The Law of Causation in the Law of Tort: Concurrent Issues

21 March 2007

Speakers James Thompson


1. This paper aims to address the problem of concurrent causes in the law of tort.  It deals exclusively with the position in tort and does not go into the realm of contractual negligence (where different issues arise).

2. The paper is in four parts, namely:

(a) Causation generally;

(b) Concurrent causes in tort – the general rule;

(c) The exception to the general rule;

(d) The rules of causation in a commercial context.

Causation generally
3. Lord Hoffmann, writing in the Law Quarterly Review, summarised the way in which the law deals with causation as follows:

“First, it is usually a condition of liability that not only should one have done, or been responsible for, some act which the law regards as wrongful, but that there should be a prescribed causal connection between that act and damage or injury for which one is held liable.  There may be other conditions as well, such as that the harm should have been foreseeable.  But some prescribed causal connection is usually required.  Secondly, the question of what should count as a sufficient causal connection is a question of law…” [1]

4. Lord Hoffmann continued to explain that the standard criteria for establishing the causal connection required (commonly known as the “but for” test) accord with ordinary moral notions of responsibility, although there may be occasions when the law deviates from the standard criteria.

5. It is clear that the test of causation is a legal test.  It helps to bear this in mind when trying to rationalise the deviations from the standard criteria in certain cases.

6. As pointed out by my colleague, Vincent Moran QC, in his paper entitled “Duties of Care in the Construction Field”, the concept of causation is closely related to the concept of “scope of duty”, such that difficult problems relating, for example, to whether a valuer who negligently overvalues land offered to his client as security for a loan should be liable for a subsequent fall in the property market [2] can be addressed using either.  I do not intend to stray into the debate as to whether such problems are properly characterised as relating to duty or causation.  Instead we shall look at what might be called “pure” questions of causation, relating to concurrent causes.

Concurrent causes in tort – the general rule

7. The general rule in tort where there are competing causes is tolerably clear.  Where none of those causes are the responsibility of the claimant, he will be able to recover against a defendant if he can establish that the cause for which the defendant is responsible caused or materially contributed to his loss.

8. In the case of Bonnington Castings v Wardlaw [1956] AC 613, Wardlaw sought damages for having contracted pneumoconiosis as a result of the accumulation of silica particles in his lungs while working in Bonnington Castings’ “dress and fettle shops”.  There were two possible sources of these particles: from a pneumatic hammer and from swing grinders.  Bonnington were liable only in respect of dust from the grinders.  The House of Lords addressed the problem thrown up by the fact that the two sources had clearly contributed to Wardlaw’s contraction of the disease.  Lord Reid held in the following terms:

“… I cannot agree that the question is: which was the most probable source of the respondent’s disease, the dust from the pneumatic hammers or the dust from the swing grinders?  It appears to me that the source of his disease was the dust from both sources, and the real question is whether the dust from the swing grinders materially contributed to the disease.  What is a material contribution must be a question of degree.”

9. The same approach was taken by the House in McGhee v National Coal Board [1973] 1 WLR 1, in which it was held that a material increase in the risk of injury was equivalent to a material contribution to the damage.  The claimant contracted dermatitis from brick dust in the brick kiln in which he worked.  His employer failed to provide washing facilities, so that he was forced to cycle home each day with the dust still on his skin.  It was not possible to prove that the condition was caused by the presence of the dust on his skin on the ride home, or whether he would have contracted it in any event due to the presence of dust during the ordinary working day.  The House held that McGhee could recover because he was able to prove that the defendant’s failure to provide facilities materially increased the risk of the condition:

“It has always been the law that a pursuer succeeds if he can show that fault of the defender caused or materially contributed to his injury.  There may have been two separate causes but it is enough if one of those causes arose from the fault of the defender.  The pursuer does not have to prove that this cause would of itself have been enough to cause him injury.”[3]

10. In Hotson v East Berkshire [1987] 1 AC 750 the House adopted the same approach.  That case involved the negligent treatment of a young boy who fell out of a tree, damaging his hip and subsequently developing necrosis.  His injury was not correctly diagnosed and, as a result, treatment was delayed by five days.  As stated by Lord Bridge at “unless the plaintiff proved on the balance of probabilities that the delayed treatment was at least a material contributory cause of the avascular necrosis he failed on the issue of causation and no question of quantification could arise.”  Accordingly the House held that the judge’s finding of fact that, on the balance of probabilities, the fall itself was the sole cause of the necrosis meant that the claimant could not recover for the “lost chance” of a better medical outcome. 

11. A similar set of facts arose in Wilsher v Essex Area Health Authority [1988] AC 1074.  The claimant, born prematurely, developed a condition in his eyes which resulted in blindness.  One of the possible causes of the condition (out of five) was the negligent insertion of a catheter and monitoring of his arterial blood oxygen levels, the result of which was that those levels were too high.  The House of Lords held that it could not be inferred from the simple fact that excess oxygen could cause the claimant’s condition that it must therefore have made a material contribution to his injury.  The case was therefore remitted for trial before a different judge.

12. Similarly, in Fairchild v Glenhaven Funeral Services Ltd [2003] 1 AC 32, the House of Lords did not depart from the general test that a “material contribution” was necessary.  I shall return to this case below.

13. From the above cases, it is clear that the claimant must show that the negligence of the defendant caused, or made a “material contribution” to, his loss.  That such a “material contribution” exists must be proved by the claimant on the balance of probabilities.  It is not sufficient to show that the defendant’s conduct increased the likelihood of damage being suffered and may have caused it.

An exception to the general rule

14. The House of Lords has recognised that an exception to the general rule can be made in cases where the state of scientific knowledge does not permit a claimant to prove the exact mechanism by which his loss was caused, such that he is unable to satisfy the usual test where he has been exposed to more than one source of, for example, asbestos fibres.

15. In Fairchild the House explicitly accepted that the above exception arises by virtue of “a strong policy argument in favour of compensating those who have suffered grave harm, at the expense of their employers who owed them a duty to protect them against that very harm and failed to do so”. [4]  It does not arise by the drawing of a factual inference.  It is simply a variation of the ordinary approach to causation.  The test applied in these sorts of case is less stringent.

16. In Barker v Corus UK Ltd [2006] 2 AC 572 the House of Lords resolved two important questions which were left undecided in Fairchild:

(a) What were the limits of the exception to the general rule?

(b) What is the extent of the liability under the exception?

17. With regard to the first question, Lord Hoffmann’s opinion was that the essential condition for the operation of the exception was that “the impossibility of proving that the defendant caused the damage arises out of the existence of another potential causative agent which operated in the same way”.[5]  Thus, where the claimant suffers lung cancer and cannot prove that exposure to asbestos is more likely to have caused his condition than his regular smoking habit, he will be unable to recover.

18. With regard to the second question, Lord Hoffmann stated as follows:

“In my opinion, the attribution of liability according to the relative degree of contribution to the chance of the disease being contracted would smooth the roughness of the justice which a rule of joint and several liability creates.  The defendant was a wrongdoer, it is true, and should not be allowed to escape from liability altogether, but he should not be liable for more than the damage which he caused and, since this is a case in which science can deal only in probabilities, the law should accept that position and attribute liability according to probabilities.”

19. Accordingly, Lord Hoffmann adopted the approach that the defendant cannot be liable for all of the loss suffered by the claimant in such cases.  He is liable only for the amount represented by the proportion of his contribution to the claimant’s loss.  Lord Hoffmann stated his hope that “practical and economic” criteria could be developed to allow for quantification of the defendant’s liability in each case.

20. The various speeches in that case need to be closely studied but, in general, the reasoning of Lord Hoffmann was adopted by the majority.

The rules of causation in a commercial context

21. The rules of causation assume real importance in construction cases in which there is more than one possible cause of the claimant’s loss.  In such cases, there will be a good argument that the claimant should succeed upon showing that the defendant’s negligence “materially contributed” to his loss, even if it was a less important cause than the others.

22. In IBA v EMI and BICC (1980) 14 BLR 1 the House of Lords held that the defendant (BICC) was liable for its negligent design of a television aerial mast, causing it to collapse as a result of oscillation of the mast during high winds.  The collapse was in fact caused by two forces of stress on the mast, but BICC were only liable in respect of one of them.  The other stress, for which BICC were not liable, was “by far the more important cause” of the collapse.  Nevertheless, the stress for which BICC was liable “materially contributed to the collapse” and Lord Fraser, at 37 and 38, applied the statement of Lord Reid in McGee quoted at paragraph 9 above to found liability.

23. Can we go further then and ask whether the exception to the general rules on causation in the law of tort is capable of application in a commercial context?

24. In my view, it is unlikely that the exception will be applied outside of the narrow facts of the cases cited above.  This is for the following reasons:

(a) The common thread of public policy runs through the judgments in those cases in which the exception has been held to apply.  See in particular the statement by Lord Bingham in Fairchild at paragraph 15 above.  It is highly unlikely that such policy arguments will apply in commercial cases;

(b) The restriction of the exception by the House of Lords in the case of Barker to those cases in which, as Lord Hoffmann put it, the impossibility of proving the causal link in the ordinary way “arises out of the existence of another potential causative agent which operated in the same way” means that it will be a very special set of facts which give rise to it.  In many commercial disputes, and particularly in those relating to large construction disputes, the difficulty in proving a causal link arises out of the existence of potential causative agents which operate in very different ways.

25. Therefore while the application of the principle in a commercial context remains possible in theory, it is thought that it will be a rare case in practice.

[1] [2005] LQR 592 at 596-597
[2] The problem addressed by the House of Lords in the case of
South Australian Asset Management Corp. v York Montague Ltd [1997] AC 191
[3] Per Lord reid at 4
[4] Per Lord Bingham at 67
[5] At 587


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