As regulator of most activities in modern society, negligence is the most important field of tort liability (Canadian Tort Law, by Allen Linden, 2001, pg 101) (“Linden”) and includes claims related to medical malpractice, personal injury, product liability and professional negligence.
The standard of care is the standard to which tort law holds people in any given situation. One breaches the standard of care by failing to conduct oneself in accordance with the standard. But how is such breach to be measured?
The primary device used to determine breach of the standard of care is called the reasonable person.
The reasonable person is not an actual person, but rather an imagined individual whose conduct lives up to the standard of care: “Negligence is the omission to do something which a reasonable man, guided upon those considerations which ordinarily regulate the conduct of human affairs, would do, or doing something which a prudent and reasonable man would not do” (Blyth v. Birmingham Water Works Co. (1856), 11 Ex. 781, at pg 784).
Importantly, the reasonable person represents an objective (rather than subjective) standard. In other words, the law requires everybody, regardless of personal idiosyncrasies, to live up to a minimum standard of performance (Linden, pg 131).
This must be the case, for if it were not, then the law would be “co-extensive with the judgment of each individual, which would be as variable as the length of the foot of each individual” resulting in “so vague a line as to afford no rule at all, the degree of judgment belonging to each individual being infinitely various” (Vaughan v. Menlove; (1837), 3 Bing. N.C. 468).
The enforcement of reasonable standards of conduct is aimed at preventing the creation of reasonably foreseeable risks (Stewart v. Pettie  1 S.C.R. 131, para 50) (“Stewart”).
However, the reasonable person is not perfect, and may even create risks. Liability will not be imposed on those who create risks that were not reasonably foreseeable because to do so would be to impose liability on those acting reasonably (Stewart, para 50). Yet, conduct will be negligent where it “creates an objectively unreasonable risk of harm” (Ryan v. Victoria (City)  1 S.C.R. 201, para 28) (“Ryan”).
What, then, is the nature of the reasonable person?
In Arland v. Taylor  O.R. 131 (“Arland”), Laidlaw J.A. described the reasonable person:
“He is not an extraordinary or unusual creature; he is not superhuman; he is not required to display the highest skill of which anyone is capable; he is not a genius who can perform uncommon feats, nor is he possessed of unusual powers of foresight. He is a person of normal intelligence who makes prudence a guide to his conduct. He does nothing that a prudent man would not do and does not omit to do anything a prudent man would do. He acts in accord with general and approved practice. His conduct is guided by considerations which ordinarily regulate the conduct of human affairs. His conduct is the standard ‘adopted in the community by persons of ordinary intelligence and prudence’” (Arland, pg 142).
Even though the reasonable person test represents an objective standard, it may be applied variously in the sense that “the measure of what is reasonable depends on the facts of each case, including the likelihood of a known or foreseeable harm, the gravity of that harm, and the burden or cost which would be incurred to prevent the injury” (Ryan, para 28).
Perhaps it is not surprising, then, that certain situations require modification of the reasonable person standard. For example, unreasonableness will mean different things for “children, those with mental disabilities, and for professional people” (Linden, pg 119).
Thus, a relaxed standard has been applied to cases involving the alleged negligence of children, whereas a higher standard is applied to those with superior knowledge, such as lawyers and doctors.
Indeed, professional people (such as those involved in medical malpractice or professional negligence claims) cannot avoid liability by performing merely to the standard of an ordinarily prudent person. Since they hold themselves out as having additional skills and experience, more may be demanded of professionals (Linden, pg 149).
Although there have been some doubts as to whether the outcomes of many cases are affected by the reasonable person test, the test, with its objective yet variously applicable standard, has stood the test of time and provided negligence law with both reliability and flexibility (Linden, pg 133).