← The hardest concepts in Australian law
In one breath
To recover in negligence the plaintiff must show that the breach caused the harm, and in the civil liability legislation of most jurisdictions that means two steps: the breach must have been a necessary condition of the harm, and it must be appropriate for the defendant’s responsibility to extend to it. At common law the High Court has said that the “but for” test is not the only test and that causation involves common sense and value judgments.
The picture
The turnstile and the usher
A stadium has two checks before you reach your seat. At the turnstile, a machine asks a plain factual question: do you have a ticket? If not, you cannot pass. That is the “but for” question: would the harm have happened without the breach? Past the turnstile, an usher asks a different sort of question: given why you came, is it fair for you to be here? An usher can turn away someone who passed the turnstile.
Many causation puzzles arise because the two checks ask different questions. A careless driver delays you, and a falling branch later strikes you where you would not have been but for the delay. The turnstile is satisfied, yet few think the driver should pay, because the harm is not of a kind that the duty and the breach were there to prevent. In the other direction, some claims are stopped at the turnstile because the evidence cannot show what would have happened, and the statutes allow the usher to let someone in exceptionally where a court thinks it appropriate.
Where the picture stops working
A ticket check is a yes-or-no question about a fact, whereas “but for” reasoning asks what would have happened in a world that did not occur, and so involves judgment. The usher’s question has no checklist either: the statutes direct the court to consider whether and why responsibility should extend. The details of the legislation differ from jurisdiction to jurisdiction.
How it really works
- 1Place the rule. The common law of causation is the same across the country. Civil liability Acts in most jurisdictions restate it in two steps, and their wording and coverage differ, so check the Act.
- 2Factual causation. Was the breach a necessary condition of the occurrence of the harm? This is the “but for” question.
- 3Exceptional cases. Where factual causation cannot be established in the ordinary way, for example where several causes were each enough, the statutes allow a court, in appropriate cases and with reasons, to treat it as established.
- 4Scope of liability. Ask whether, and why, the defendant’s responsibility should extend to the harm. Relevant matters include whether the harm was within the risk that made the conduct careless, intervening acts of others, and policy.
- 5Proof. The plaintiff proves causation on the balance of probabilities, and the court may draw reasonable inferences. In failure-to-warn cases, statutes in some places limit the weight of the plaintiff’s own later evidence of what they would have done.
Why people get it wrong
- Treating “but for” as the whole test. The statutes add the scope step, and the common law has never accepted it as the only test.
- Treating every necessary condition as a legal cause. Countless conditions are necessary to any event.
- Forgetting that the intervening act of a third person can limit the scope of liability.
- Assuming causation is purely a matter of science. Value judgments about responsibility are part of it.
- Confusing causation with remoteness or with the assessment of damages.
A worked example
The facts are invented
Joss, a tradesperson, leaves an unlit trench across a footpath at night, contrary to a council rule. Arun, walking, does not see the trench, falls in and breaks his leg. But for the missing lights he would not have fallen, and the injury is within the very risk that makes leaving a trench unlit careless. Both steps are met.
Change the facts: Arun sees the trench in time, steps onto the road to avoid it, and is hit by a speeding drunk driver. But for the trench he would not have been on the road, so the first step may be met. The second step asks whether Joss should answer for what a reckless driver did, and the answer may well be no.
Try it
A builder carelessly delivers materials an hour late. Because of the delay, a worker is on site when an unrelated and unforeseeable lightning strike injures him. He would not have been there but for the delay. What is the best analysis?
Landmark authorities
Read the sources themselves; this list is a starting point.
- March v E & M H Stramare Pty Ltd, (1991) 171 CLR 506
- Chappel v Hart, (1998) 195 CLR 232
- Adeels Palace Pty Ltd v Moubarak, (2009) 239 CLR 420
- Wallace v Kam, (2013) 250 CLR 375
Where to go next
Dictionary
More hard concepts in Australia law
- The duty of care and salient features (Tort law)
- Occupiers’ liability (Tort law)
This page is an educational overview. It is not legal advice and not a substitute for the sources: the statute, the rule, the case itself. Australia is a federation: the Commonwealth, the six States and the Territories each make law, and the High Court is the final court for all of it. The common law, by contrast, is one law across the country. Each page says whether the rule is constitutional, federal or common law shared by every jurisdiction, or State-by-State legislation that varies, and flags where the States and Territories differ. Each page states the usual formulation of the rule and names landmark decisions; check the primary sources of your own jurisdiction before relying on any rule.