McGill Faculty of Law: Extra-Contractual Obligations/Torts: Prof. Lara Khoury, 2002-03/Summary by Derek McKee
Uncertainty often arises in cases of alternative causes: cases where injury can only have been caused by one of a series of causes, but it’s impossible to know which.
In cases with alternative causes, it’s impossble to prove that the defendant’s fault played any role.
It’s therefore impossible to meet the requirements for the balance of probabilities and the burden of proof.
The courts have responded in three ways:
1. reversal of the burden of proof of causation (based on risk)
In this approach, the plaintiff asks the court to shift the burden to the defendant.
If the court accepts and the evidence is 50-50, the plaintiff wins.
Pure reversal of the burden of proof actually withdraws any requirement to prove anything about the element in question.
There can also be partial reversal of the burden of proof.
This was a minority view in McGhee (Lord Wilberforce) and Gburek v. Cohen (Beauregard J.). It was rejected in Farrell v. Snell (Sopinka J.).
McGhee v. National Coal Board,  3 All E.R. 1008 (H.L.). (CB1p530)
McGhee worked in a brick kiln; it was very dirty work and no showers were provided. He had to shower after bicycling home. Later, he contracted dermatitis. The court found that the employer had a duty to provide showers. However, it was not clear whether the dermatitis was caused by the absence of showers.
What was required in order to establish that the absence of showers caused the dermatitis?
It had to be shown that the absence of showers materially contributed to the risk.
Lord Reid inferred causation based on increase of risk/material contribution. (He refused to distinguish between the two.)
Lord Wilberforce (in the minority, but not dissenting) shifted the burden of proof to the defendants based on increase of risk.
Lord Simon of Glaisdale held that “substantial contribution” was enough; he also said that in a case which involves a risk, “failure to materially reduce the risk” and “substantial contribution to the injury” are equivalent.
Lord Simon held (with Lord Reid) that it was useless to distinguish between material contribution to the injury and material increase of the risk of injury.
2. presumption/inference of causation (sometimes based on increased risk)
This is a factual presumption as opposed to a legal presumption: it is not provided for in any statute.
If a party is unable to prove a fact directly, it might ask a judge to infer the fact from proven facts. (e.g. train derailment—rock fell from truck?)
The judge has discretion.
Common law’s “inferential reasoning process” is to the same effect.
This method was the majority in McGhee, Gburek v. Cohen, Farrell v. Snell and Laferrière v. Lawson.
Gburek c. Cohen,  R.J.Q. 2424 (C.A.). (CB1p512)
Gburek, who was paraplegic and used a wheelchair, was admitted to the hospital with a high fever due to an infection in his back. In the emergency, Dr. Cohen administered a powerful antibiotic, gentamycine, which was known to have possible side-effects on hearing. The gentamycine treatment continued for 40 days with no hearing tests, until one day, Gburek apparently lost his hearing all of a sudden. Cohen was found to be at fault for not administering hearing tests. Although it was found that the gentamycine caused the hearing loss, it was unclear whether earlier hearing tests could have