The ‘but for’ test of causation in Australian law

To ensure the damage element of a negligence claim is satisfied, a plaintiff must prove the loss was caused by the act or omission of the defendant. With the enactment of Australia’s various Civil Liability Acts, the test for factual causation is the ‘necessary condition’ test. The plaintiff must establish that the alleged breach of duty by the defendant was a necessary condition of the occurrence of the harm.

The High Court in Strong v Woolworths Ltd1 has stated that this necessary condition test is a ‘statutory statement of the “but for” test of causation’. The ‘but for’ test determines whether the harm suffered by a plaintiff was caused by the breach of the defendant’s duty, on the basis the plaintiff would not have suffered harm ‘but for’ the defendant’s breach. The test requires a relatively straightforward question: but for the defendant’s negligence, would the plaintiff’s damage have occurred?

However, there are instances where the ‘but for’ test is inadequate because, in light of evidential gaps in causation, the ‘but for’ analysis will preclude a finding of factual causation. Two such cases are highlighted by the UK decisions of Fairchild v Glenhaven Funeral Services Ltd & Ors (Fairchild)2 and Bonnington Castings Ltd v Wardlaw (Bonnington Castings)3.


In Fairchild, there were three cases whereby each claimant worked for different employers and during the course of their duties, were exposed to and inhaled asbestos dust and fibres. It was found that each employee had contracted mesothelioma as a result of the employers’ wrongful conduct, which ultimately lead to their deaths. 

As there were multiple employers who exposed the claimants to asbestos, it was held the ‘but for’ test could not be applied to determine that the claimants would not have suffered from mesothelioma ‘but for’ any one or more employer’s breaches of duty. This is because an ‘evidential gap’ existed, meaning it was impossible to determine which of a number of multiple sufficient causes gave rise to the disease.

In considering causation, the predominant issue was ‘whether, in the special circumstances of such a case, principle, authority or policy requires or justifies a modified approach to proof of causation’.4 The House of Lords found that it was impossible to establish on the balance of probabilities that the employers’ breach of duty caused the claimants to suffer from mesothelioma. The House of Lords therefore adopted the approach taken in McGhee v National Coal Board5 and held that the employers ‘individually materially increased the risk6 of the employees contracting mesothelioma and consequently allowed the employees to succeed against each defendant employer.  

Bonnington Castings

In Bonnington Castings, an employee contracted pneumoconiosis, which is a disease caused by the gradual accumulation of silica dust particles in the lungs. There were several sources of exposure to the silica dust from the equipment in the employee’s workplace:

  • a pneumatic hammer (which spread silica dust, but as there was no way to prevent this, gave rise to no breach of duty by the employer);
  • a floor grinder (which the employee did not make any complaints in relation to); and
  • swing grinders (where an improper set-up of the equipment increased silica dust flow and was found to be in breach of duty).

The state of scientific knowledge at the time did not enable proof as to which dust from which item of equipment had caused the employee’s pneumoconiosis. It was however found that the greater proportion of the employee’s exposure to silica dust was generated by the pneumatic hammer (which did not give rise to a breach of duty).

In considering whether the breach regarding the use of the swing grinder was causative of the employee’s disease, Lord Reid said ‘the real question is whether the swing grinders “materially contributed” to the disease’.7 His Lordship concluded by stating that ‘it is proved not only that the swing grinders may well have contributed but that they did in fact contribute a quota of silica dust which was not negligible to the [employee’s] lungs and therefore did help to produce the disease’.

Material contribution’ was applied in this context where the ‘but for’ test could not be applied. This was because it could not be said that ‘but for’ the ‘quota of silica dust’ contributed to by the employer’s negligence (via the swing grinders), the employee would not have developed the disease. As the gradual exposure to silica dust over time had caused the employee’s pneumoconiosis, no single part of that gradual exposure could meet a ‘but for’ test.

How Australia’s Civil Liability Acts deal with these ‘exceptional cases’

The various Australian States and Territories enacted legislation following the Review of the Law of Negligence 2002, which is commonly referred to as the Ipp Report. Among other things, the Ipp Report considered instances like those in Fairchild and Bonnington Castings in which a finding of factual causation could not be made by utilising the ‘but for’ test. 

The Ipp Report considered that in certain circumstances it might be appropriate to allow proof that negligent conduct materially contributed to harm or the risk of harm, to satisfy the requirement for proof of factual causation. It was suggested that legislative provision should be made to bridge that ‘evidentiary gap’ in appropriate cases.

In response to the Ipp Report, Australia’s various Civil Liability Acts provide an alternative means of establishing factual causation in ‘appropriate’ or ‘exceptional’ cases where a breach of duty cannot be established as a necessary condition of the harm.8 Although the various Acts deal with the issue slightly differently, generally speaking the courts are required to consider, in accordance with established principles, whether or not and why responsibility for the harm should be imposed on the party in breach. That is, whether and to what extent ‘established principles’ warrant a departure from the ‘but for’ test for causation.

Courts have been reluctant to interpret such provisions as allowing a departure from the ‘but for’ test of causation beyond those contemplated in the cases of Fairchild and Bonnington Castings. Without some analogy to cases like Fairchild and Bonnington Castings, it appears unlikely any exception to the ‘but for’ test will be found.

For instance, the provisions will not apply to cases where the evidence does not establish factual causation (where there could be evidence to support a finding of a necessary condition, but no such evidence is adduced). Rather, such provisions will only apply to cases in which there cannot be such evidence because of the nature of the case.9 Courts have refused to find that it is an exceptional or appropriate case to depart from the ‘but for’ test of causation merely because a plaintiff is only able to establish the defendant’s fault may have been a cause of the harm or might have prevented its occurrence.10


The various Civil Liability Acts confirm that factual causation requires the answering of the ‘but for’ causal question. That is, the harm would not have occurred ‘but for’ the breach of duty. Alternatively, the breach of duty will not be a cause of the harm if the harm would have been suffered in any event.

Mere proof by a plaintiff of the possibility that a defendant’s breach caused the plaintiff to suffer harm is insufficient. The court must be satisfied on the balance of probabilities that the defendant’s breach caused the relevant harm.

There are exceptional cases where the single ‘but for’ causal rule is not an appropriate test. These include instances where there are two or more events or acts which would each be sufficient to bring about the plaintiff’s harm. The Civil Liability Acts provide an alternative means of establishing factual causation in such cases, however they may be limited to instances where negligent conduct materially contributed to harm or the risk of harm.   

So far, the courts have been more inclined to articulate when such cases will not arise, rather than when they will. It is clear that if a claim is brought for harm arising from an alleged breach of duty, before a court departs from the test of ‘but for’ causation, there must be a justifiable basis (in accordance with established principles) for doing so.

1 (2012) 226 CLR 182.
2 [2002] UKHL 22.
3 [1956] AC 613.
4 Fairchild, per Lord Bingham of Cornhill [2].
5 McGhee v National Coal Board [1972] UKHL 7.
6 Fairchild, per Lord Rodger of Earlsferry [168].
7 [621].
8 Civil Liability Act 2003 (Qld) s 11(2), Civil Liability Act 2002 No 22 (NSW) s 5D(2), Wrongs Act 1958 (VIC) s 51(2), Civil Liability Act 2002 (TAS) s 13(2), Civil Liability Act 1936 (SA) s 34(3), Civil Liability Act 2002 (WA) s 5C(2), Civil Law (Wrongs) Act 2002 (ACT) s 45(3).
9 East Metropolitan Health Service v Ellis (by his next friend Ellis) [2020] WASCA 147.
10 Adeels Palace Pty Ltd v Moubarak (2009) 239 CLR 420.

This article may provide CPD/CLE/CIP points through your relevant industry organisation.

Mark Brookes
Greg Stirling
Special Counsel
Hayley Nankivell

Related insights

Goddard v Richtek Melbourne Pty Ltd [2024] FWC 979

14 May 2024
Read more

Revisiting the duty of utmost good faith (and a win for insurers)

1 February 2024
Read more

The consequences of no notification revisited: Fairbank Haven v Merkon Constructions

1 February 2024
Read more

The NSW Court of Appeal Confirms the Scope of a Solicitor’s Duty to Advise Clients

3 March 2023
Read more