Causation - 'But For' II. Stevenhaagen Estate v. Kingston General Hospital
In Stevenhaagen Estate v. Kingston General Hospital (Ont CA, 2022) the Court of Appeal considered causation in a medical malpractice case:
 The trial judge properly identified the test for causation established in Clements v. Clements, 2012 SCC 32,  2 S.C.R. 181. He specifically referenced McLachlin C.J.’s prescription, at para. 9 (of Clements): “The ‘but for’ causation test must be applied in a robust common sense fashion. There is no need for scientific evidence of the precise contribution the defendant’s negligence made to the injury.”. Owen v. Bains
(b) Applying the “but for” Test
 The appellants submit that the trial judge did not properly apply the “but for” test. They submit that he unduly focused on medical causation, as opposed to factual causation. That is, the trial judge failed to come to terms with what actually happened to Ms. Stevenhaagen, when did her injuries occur, and most critically, would her outcome have been any different had the doctors not been negligent.
 The appellants rely on the decision of this court in Sacks v. Ross, 2017 ONCA 773, 417 D.L.R. (4th) 387, leave to appeal refused,  S.C.C.A. No. 491, a case that also turned on the issue of causation. Writing for the court, Lauwers J.A. discussed the proper causal reasoning process in the following way, at paras. 47 and 48:
Regardless of whether the defendant's breach of the standard of care is an act or an omission, the trier of fact's cognitive process in determining causation has three basic steps. The first is to determine what likely happened in actuality. The second is to consider what would likely have happened had the defendant not breached the standard of care. The third step is to allocate fault among the negligent defendants.See also paras. 98-100.
There are two possible outcomes to the trier of fact's imaginative reconstruction of reality at the second step. On the one hand, if the trier of fact draws the inference from the evidence that the plaintiff would likely have been injured in any event, regardless of what the defendant did or failed to do in breach of the standard of care, then the defendant did not cause the injury. On the other hand, if the trier of fact infers from the evidence that the plaintiff would not likely have been injured without the defendant's act or failure to act, then the "but for" test for causation is satisfied: but for the defendant's act or omission, the plaintiff would not have been injured. The defendant's fault, which justifies liability, has been established.
In Owen v. Bains (Div Ct, 2021) the Divisional Court considered an issue of 'but for' causation:
 Typically, the question of causation is considered by the trier of fact once it is established that a defendant has breached a duty of care.. Uribe v. Tsandelis
 The “but for” test with respect to causation was set out in the decision in Clements v. Clements, 2012 SCC 32,  2 S.C.R. 181 at para 8:
The test for showing causation is the “but for” test. The plaintiff must show on a balance of probabilities that “but for” the defendant’s negligent act, the injury would not have occurred. Inherent in the phrase “but for” is the requirement that the defendant’s negligence was necessary to bring about the injury ― in other words that the injury would not have occurred without the defendant’s negligence. This is a factual inquiry. If the plaintiff does not establish this on a balance of probabilities, having regard to all the evidence, her action against the defendant fails.
In Uribe v. Tsandelis (Ont CA, 2021) the Court of Appeal set out the basics of the 'but for' causation doctrine, and how the use of the term 'contribution' may lead to confusion:
 Once it is established that the defendant has breached the duty of care, the trier of fact moves to consider causation. The but for test for causation was set out in Clements v. Clements, 2012 SCC 32,  2 S.C.R. 181, at para. 8:
The test for showing causation is the “but for” test. The plaintiff must show on a balance of probabilities that “but for” the defendant’s negligent act, the injury would not have occurred. Inherent in the phrase “but for” is the requirement that the defendant’s negligence was necessary to bring about the injury ― in other words that the injury would not have occurred without the defendant’s negligence. This is a factual inquiry. If the plaintiff does not establish this on a balance of probabilities, having regard to all the evidence, her action against the defendant fails. [Emphasis in original.] The appellant argues that the jury did not apply this test, but rather applied the material contribution test, which the jury was not charged on. The parties on appeal agree that the but for test was the correct test to charge the jury on and that the material contribution test did not apply to these facts. The appellant points to the jury’s answer to question 2(b):
The fact that Dr. Tsandelis didn’t follow the SOGC Guideline, “prepare for delivery”, contributed to [the baby’s] eventual brain damage. [Emphasis added.] I do not agree that the jury’s words “contributed to” mean that the material contribution test was applied. The words responded to the questions asked and – as jurisprudence demonstrates – are consistent with the but for test.
 The jury was asked to determine causation and then to determine allocation. Note the jury instructions:
[C]ausation is established if the evidence satisfies you that it is more likely than not that [the baby] would not have suffered brain damage but for the negligent conduct or breach of the standard of care by Dr. Tsandelis. In other words, although you do not have to find that it was the sole cause, does the evidence prove that the negligent conduct...was necessary to bring about [the baby’s] brain damage. [Emphasis added.]And further:
[T]he defendant’s conduct need not be the sole cause. It does not have to be the most important cause. However, it must have been a necessary cause of the harm. The plaintiffs must show on a balance of probabilities that the injury would not have occurred without the defendant’s negligence. Depending on your answers to some of the questions, you will be asked to determine the issue of causation with respect to Dr. Tsandelis and the nurses and Grand River Hospital. If you find that the acts or omissions of both Dr. Tsandelis and/or the nurses and/or the Grand River Hospital caused [the baby]’s brain damage, then as I pointed out to you earlier, you’ll be required to apportion a degree of responsibility of each party as I pointed out in reviewing the question. [Emphasis added.] It is not surprising that, when there is more than one potential tortfeasor, language relating to contribution would arise. This is particularly so when the jury is also required to apportion damages. This was addressed in Clements at para. 12:
In some cases, an injury — the loss for which the plaintiff claims compensation — may flow from a number of different negligent acts committed by different actors, each of which is a necessary or “but for” cause of the injury. In such cases, the defendants are said to be jointly and severally liable. The judge or jury then apportions liability according to the degree of fault of each defendant pursuant to contributory negligence legislation. When the jury is asked to consider contributory negligence, it is understandable that it would use the language of “contributed to”. It does not mean that the instructions with respect to the but for test or causation were not followed, or that the jury applied the material contribution test. The jury response continued to state that, if Dr. Tsandelis had met his duty by preparing for delivery after the first deceleration, “the O.R. would have been ready for Maria & [the baby] would have been delivered sooner avoiding the asphyxia altogether.” This response indicates that the jury concluded that, but for the appellant’s failure to meet the standard of care, the brain damage would not have happened.
 As this court recently said in Donleavy v. Ultramar Ltd., 2019 ONCA 687, 60 C.C.L.T. (4th) 99, at para. 72:
Even in the “but for” context, there are situations involving multiple defendants where courts have used “contribution” language to recognize that a defendant’s negligence is “a” cause of the plaintiff’s injury. This is a potential source of confusion. The phrase “caused or contributed” is used in the Negligence Act, R.S.O. 1990, c. N.1, s. 1. As Lauwers J.A. observed in Sacks v. Ross, 2017 ONCA 773, 417 D.L.R. (4th) 387, leave to appeal refused  S.C.C.A. No. 491, at para. 117, this is the way the causation test has been described in several cases in the Supreme Court (including as I noted earlier in Athey), and in this court; see also White v. St. Joseph’s Hospital (Hamilton), 2019 ONCA 312, at para. 25. Causation is made out under the “but for” test if the negligence of a defendant caused the whole of the plaintiff’s injury, or contributed, in some not insubstantial or immaterial way, to the injury that the plaintiff sustained. Causation requires a “substantial connection between the injury and the defendant’s conduct”: Resurfice, at para. 23, Clements, at paras. 20-21, 28. As Paciocco J.A. noted in Smith v. Safranyos, 2018 ONCA 760, at para. 128, McLachlin C.J.C.’s reference to “a robust and common sense application of the ‘but for’ test of causation” is a “manifestation of this limit”. Used in this way, the conclusion that one or more defendants “materially contributed” to a plaintiff’s injury or loss simply recognizes that the defendant’s negligence was not the only cause. Likewise, here. The jury’s statement that the appellant’s conduct contributed to the damage merely recognizes that there was more than one cause. Note that in Donleavy, this court was considering the words of a trial judge, not a jury comprised of lay persons.
 When there is more than one tortfeasor, contributory language might arise. It does not mean the wrong causation test was used. It is clear from the jury’s answer that the proper test was used.