The standard of care in negligence is famously impersonal. A defendant is evaluated not by what he could have foreseen but by what a reasonable person in his circumstances would have foreseen, and his own limitations -- inexperience, deficient judgement, a slow mind -- do not enter the calculation. Critics have characterised this as unjust, and the criticism possesses an obvious force: a learner driver is held to the standard of a competent one, and consequently a beginner doing his conscientious best may incur liability where a practised driver doing rather less would not.
The objection presupposes that the standard is a description. It is not; it is an allocation. Between two blameless parties -- a defendant who did his best and proved insufficient, and a claimant who has sustained a loss through conduct falling below what people are entitled to expect -- the law must place a loss somewhere, and the reasonable person is the instrument by which it determines where. Interpreted that way, the learner driver is not an anomaly but the clearest statement of what the standard does: a person who takes a car onto a road undertakes to drive it as a driver, and whether he can is his own affair.
This becomes plainer where the standard is relaxed. Children are evaluated against children of their age, and the justification offered is not that a child's mind differs in kind from an inexperienced adult's -- it may not -- but that a child's presence on the road or in the playground is not something he has undertaken. The child has held himself out as nothing. The learner has. Where the courts have individualised, in other words, they have done so on the basis of what the defendant undertook rather than what he was equipped for. The same interpretation explains why a defendant acting in a sudden emergency is not measured against a person who had time to deliberate: the emergency is not part of what he undertook.
The pattern holds at the other end of the scale. A defendant who professes a skill is evaluated by the standard of those who possess it, and by that standard exclusively: a surgeon may not plead that he is a poor surgeon, and an unusually gifted one is not required to be exceptional. What is measured throughout is not the person but the undertaking, and the impersonality of which critics complain is the mechanism by which undertakings are made to mean something.
None of this demonstrates the standard to be just. It demonstrates that the customary objection misses its target. A rule that allocates loss according to what people have held themselves out as able to do may still be a bad rule. It will not be a bad rule for the reason that it fails to describe the defendant's mind, because describing his mind was never among its purposes.
