The decision undoes the inflexible approach of previous unaninimous High Court decisions (Smith v Jenkins and Gala v Preston) that one illegal user of a vehicle does not owe a duty of care to a passenger complicit in the illegal use.
The facts can be stated briefly, and sound like they've been lifted from a torts law exam:
Danelle stole a car. She moved into another seat of the car and allowed Maurin to drive it. She knew that he had been drinking, and probably that he was unlicensed. Maurin started driving the car dangerously. Danelle asked to be let out. Maurin continued, crashed the car and Danelle was seriously injured as a result.
The majority (French CJ, Gummow, Hayne, Crennan, Keiffel and Bell JJ) posed the question they had to answer [at 5]:
Can Danelle recover damages for negligence from Maurin? Does her theft of the car, or her subsequent use of the car (or some combination of both her theft and her use of the car), defeat her claim for damages for negligence?
In some Australian jurisdictions the issue would be resolved by a specific statutory provision regulating the recovery of damages for personal injury suffered when the plaintiff was acting illegally. Western Australia doesn't have one so the issue was determined by the common law. (Section 14G(2)(b) in Part IIB of the Wrongs Act 1958 (Vic.) provides that a plaintiff's illegal activity must be considered in a claim for damages, but it doesn't specify how).
The majority began by basically writing off the illegality doctrine of ex turpi causa non oritur actio as inapplicable to negligence (though the Court did acknowlege [at 15] that the law in this respect needs to remain congruent with the rest of the civil law, notably contract and trusts.) The Court found the maxim to be vague and unhelpful.
Ultimately, the question is: would it be incongruous for the law to proscribe the plaintiff's conduct and yet allow recovery in negligence for damage suffered in the course, or as a result, of that unlawful conduct? Other questions, such as whether denial of liability will deter wrongdoers or advantage some at the expense of others, are neither helpful nor relevant. And likewise, resort to notions of moral outrage or judicial indignation serves only to mask the proper identification of what is said to produce the response and why the response could be warranted.
The relationship between the parties in a negligence action is the foundation of the tort. Here, the Court drew attention to the fact that different ways of defining the relationship between Danelle and Maurin suggested contrary outcomes [at 47]:
One aspect of the relationship between the parties in the present case was that they were joint participants in an illegal act. Another aspect of their relationship was that the plaintiff was a passenger in a motor vehicle being driven by the defendant. The relationship between the parties could therefore be described as a relationship of passenger and driver. But, just as it is wrong to describe the relationship between them only as that of participants in a joint criminal enterprise, it is wrong to describe their relationship only as that of passenger and driver. Both characterisations of the relationship are accurate, but neither is complete. Both characterisations must be applied to describe the relevant circumstances fully.
Edit: The majority held that Danelle was a party to the theft. Consequently, she was a party to the bad driving through the operation of s 8 of the WA Criminal Code.
8. Offences committed in prosecution of common purpose
(1) When 2 or more persons form a common intention to prosecute an unlawful purpose in conjunction with one another, and in the prosecution of such purpose an offence is committed of such a nature that its commission was a probable consequence of the prosecution of such purpose, each of them is deemed to have committed the offence.
(2) A person is not deemed under subsection (1) to have committed the offence if, before the commission of the offence, the person —
(a) withdrew from the prosecution of the unlawful purpose; and
(b) by words or conduct, communicated the withdrawal to each other person with whom the common intention to prosecute the unlawful purpose was formed; and
(c) having so withdrawn, took all reasonable steps to prevent the commission of the offence.
The High Court held that dangerous driving was a probable consequence of the theft of the car. But the Court also accepted that Danelle had withdrawn from that purpose by asking to be let out. (See the comments attached to this post for a discussion of why that interpretation is questionable. And particular thanks to Jeremy Gans for his analysis.)
Heydon J wrote his own judgment in dissent, broadly in agreement on many points but outlining a hypothetical series of arguments he would have run if he been acting for the respondent. (I predict we're going to see more and more of this kind of thing from Heydon J during his remaining 3 years on the bench). He held that the request to get out was insufficient to constitute a withdrawal from the criminal enterprise.
I've criticised the High Court's judgments lately. Miller is a case that does involve a more comprehensive critique of previous cases and a bolder approach to legal principle. But in this case the principle arrived at was each case needs to be dealt with on its merits.