McGill Faculty of Law: Extra-Contractual Obligations/Torts: Prof. Lara Khoury, 2002-03/Summary by Derek McKee
that it was reasonably foreseeable for Dr. Murray that his error would mislead other doctors who would treat Price. He stated a rule: “…a person doing a negligent act may, in circumstances lending themselves to that conclusion, be held liable for future damages arising in part from the subsequent negligent act of another, and in part from his own negligence, where such subsequent negligence and consequent damage were reasonably foreseeable as a possible result of his own negligence.” This decision qualified Mercer v. Gray for policy reasons. The court wanted to make doctors responsible for the effects of their negligence on subsequent diagnoses.
If the second cause was not a non-faulty medical error, this would be a difficult case for novus actus interveniens in common law.
Novus actus interveniens has been a complex issue in common law, but hasn’t been discussed so much in civil law. Civil law has usually just used the criterion of the gravity of the faults.
Subsequent Events and Aggravation of Injuries
In cases where indivisible damage is caused by two unrelated events, one faulty and one innocent, is it fair to hold the faulty defendant liable for the entire injury?
There are three possibilities:
The defendant could be held liable for the whole injury, regardless of the non-faulty event.
The defendant could still be held liable, but with damages discounted for the non-faulty event.
If the non-faulty event occurred later, it could be considered a novus actus interveniens.
In both systems, at the causation stage, the defendant can generally be held to have caused the entire indivisible damage, even if a non-faulty event was also involved.
In common law, if you “materially contributed” to the production of the damage, you are held to have caused all of it.
“Material contribution” is a common law term only; it means more than a de minimis, mininal, negligible contribution.
Civil law says that as long as your contribution is not negligible, you can be held liable.
However, at the assessment of damages stage, damages can be discounted for the contribution of non-faulty events.
At this point, unlike with causation, the burden of proof is on the defendant.
This is based on the principle that the plaintiff should not be enriched by the damages, just restored to his previous position. Courts therefore ask what position the defendant would have been in if the fault had not occurred.
There are two main scenarios, depending on whether the fault or non-faulty event comes first.
Scenario 1: If the non-faulty event precedes the fault:
The above rules apply; in this case, it is consistent with the thin-skull rule.
Athey v. Leonati,  3 SCR 458. (CB2p171)
Athey was an auto mechanic who had a history of minor back problems. He was hurt in a car accident, which caused back pain and stiffness. A few months later, he was on his way to recovery when he was hurt in another car accident, again causing minor injuries. He underwent further physiotherapy and chiropractic treatments, and was again recovering, when, while stretching, he suffered a disc herniation. He was no longer able to do any heavy physical work and he had to take a lower-paying job.
Could the some of the liability be discounted due to Athey’s pre-existing back problems?
Major J wrote, “It has long been established that a defendant is liable for any injuries caused or contributed to by his or her negligence. If the defendant’s conduct is found to be a cause of the injury, the presence of other non-tortious contributing causes does not reduce the extent of the defendant’s liability.”