What knowledge is required to start the clock running?

Some additional guidance as to the kind of knowledge that is required to start the clock running, or the circumstances in which plaintiffs ought to have known when the elements of negligence were in place, was given by our Court of Appeal in Hill, where Cote J.A., speaking for the court said: Even if the discoverability rule of limitations applies to this case (which I need not decide), it does not call for perfect certainty. It does not require discovery at all: it says something else will do instead. It suffices that ‘the material facts on which [the cause of action] is based ... ought to have been discovered by the plaintiff by the exercise of reasonable diligence ...’: Central Trust v. Rafuse [1987] 2 S.C.R. 147, 224. If the plaintiff is told a fact by someone who is likely to know, surely that makes the fact known or discoverable, even if the someone else disputes the fact. Very few people who sue have perfect certainty.