To what extent have rules concerning causation been modified to meet the demands of justice in tort cases? It is important to analyse this question by considering both factual and legal causation. Causation is concerned with the 'physical connection between the defendant's negligence and the claimant's damage'. A defendant will not be held liable if his/her negligence is not the cause of the claimant's damage. The concept of factual causation uses a 'but for' test to establish where responsibility for the damage caused should lie.
If harm to the claimant would not have occurred 'but for' the defendant's negligence or omission then that negligence or omission is the cause of the harm. The 'but for' test removes irrelevant factual causes. Legal causation will then determine what relevant cause is the substantial cause of the result to establish whether a defendant is guilty for the claimant's damage. Therefore, causation seeks to establish a fair and just result between claimant and defendant. The 'but for' is useful when suited to simple and straightforward fact situations.
In Barnett v Chelsea *1, a doctor negligently treated a patient, who was later found to have died from arsenic poisoning. Would the patient have died 'but for' the doctor's negligence? The answer is yes and the doctor's negligence was found not to have caused the death. It is apparent that this test is ill suited to complex fact patterns involving multiple causal factors. In Cook v Lewis *2, where two hunter discharged their guns at the same time, negligently shooting the victim standing nearby. 'In the case of two simultaneous wrongs to the claimant…
the test produces the ludicrous conclusion that neither wrong caused the harm' [Strachan 1970]*3. The Supreme Court of Canada overcame that problem by holding that, in such circumstances, once the plaintiff had established that he had suffered harm, the onus shifted to the defendants to prove that their acts were neither intentional nor negligence. This is a clear modification of the proof of causation rules, which state, 'it is for the claimant to prove, on the balance of probabilities, that the defendant's breach of duty caused the damage'.
This modification shows how the conventional rules of causation would produce an injustice to the victim, whose damage would be irrecoverable. To 'meet the demands of justice', the proof of causation rule was modified. Despite this, the Cook v Lewis rule should only be applied in cases where the number of potentially guilty defendants is small. In cases with large numbers of potential tortfeasors (i. e. Wintle v Conaust *4 – five possible tortfeasors), the rule strictly applied might result in, as Prof.
Fridman stated; 'guilt by association,' an intolerable and unacceptable attitude for the law to adopt. " Therefore, the modification was limited with the demands of justice in mind. Cook v Lewis showed the courts were willing to adjust conventional rules for the sake of justice. In Bonnington Castings Ltd v Wardlaw  there are also modifications of rules in the pursuit of justice. The plaintiff (W) contracted pneumoconiosis from inhaling silica dust in his workplace.
While the main source of dust was from pneumatic hammers (innocent dust) for which the defendants (B) were not in breach of duty, some of the dust (guilty dust) came from saw grinders, which B were in breach as they failed to maintain dust extracting equipment. On this evidence, W could not prove 'but for' causation as B's negligence made it only 'more probable' that he would contract the illness. Despite this, the House of Lords determined from an 'inference of facts' from the case that the 'guilty' dust had 'materially contributed' to W's illness and B was made to pay full damages.
This case modified the conventional burden of proof on the claimant. The claimant only had to prove a 'material contribution' to the damage, rather than the conventional 'but for' requirement. This modification appears to meet the demands of justice. It is impossible for the claimant to 'even approximately quantify' (Nicholson v Atlas *5) the contributions of 'guilty' dust and physically connect it to his damage. This would exempt the defendant's liability on an unjust technicality.
It is quite clear that the defendants have been negligent and the 'guilty' dust did contribute to the W's damage, which leads to the conclusion that 'justice' would hold B liable. The courts decision in McGhee *6 modified the rules further. The claimant (M) was exposed to brick dust longer than necessary whilst working due to the defendants (C) negligence in not providing a shower to wash after work. The claimant later suffered from dermatitis caused by the brick dust. He could not prove 'but for' causation that a shower after work would have prevented him from contracting the disease.
However, the House of Lords found that if the claimant could prove that the defendant's had 'materially increased the risk' faced by the claimant this is enough to find the defendant liable for the damage caused, as it is equivalent to a 'material contribution'. It was also found that the onus of the 'burden of proof' should shift to the defendant to disprove the causal link if the claimant can prove the defendant has breached his duty and this has contributed to an increased risk.
Due to the current state of medical knowledge, neither side can conclusively prove the causal link. Do these modifications meet the demand of justice? Ultimately, one side has to suffer from the 'inherent evidential difficulty' (Lord Wilberforce) and it was determined that 'justice' should condemn the 'creator of the risk' who 'must be taken to have foreseen the possibility of damage, who should bear the consequences'. Therefore it seems justifiable that the defendants should be held liable.