§ 142 The Standard of Care
Carelessness is not culpable, or a ground of legal liability, save in those cases in which the law has imposed a duty of carefulness. In all other cases complete indifference as to the interests of others is allowable. No general principle can be laid down, however, with regard to the existence of this duty, for this is a matter pertaining to the details of the concrete legal system, and not to abstract theory. Carelessness is lawful or unlawful, as the law sees fit to provide. In the criminal law liability for negligence is quite exceptional. Speaking generally, crimes are wilful wrongs, the alternative form of mens rea being deemed an insufficient ground for the rigour of criminal justice. This, however, is not invariably the case, negligent homicide, for example, being a criminal offence. In the civil law, on the other hand, no such distinction is commonly drawn between the two forms of mens rea. In general we may say that whenever an act would be a civil wrong if done intentionally, it is also a civil wrong if done negligently. When there is a legal duty not to do a thing on purpose, there is commonly a legal duty to take care not to do it accidentally. To this rule, however, there are certain exceptions—instances in which wrongful intent is the necessary basis even of civil liability. In these cases a person is civilly responsible for doing harm wilfully, but is not bound to take any care not to do it. He must not, for example, deceive another by any wilful falsehood, but unless there is some special ground of obligation in the case, he is not answerable for false statements which he honestly believes to be true, however negligent he may be in making them.364 Other instances of the same sort are based upon the express or implied agreement or understanding of the persons concerned. Thus the gratuitous lender of a chattel is bound to disclose any dangerous defects which he actually knows of, but is not bound to take any care whatever to see that it is safe, or to discover and disclose defects of which he is ignorant. For he who borrows a thing gratuitously agrees impliedly to take it as it is, and to run all risks. But he who hires a thing for money is entitled to the exercise of due care for his safety on the part of the owner.365
Carelessness may exist in any degree, and in this respect it differs from the other form of mens rea. Intention either exists or it does not; there can be no question of the degree in which it is present. The degree of carelessness varies directly with the risk to which other persons are exposed by the act in question. He is careless, who, without intending evil, nevertheless exposes others to the danger of it, and the greater the danger the greater the carelessness. The risk depends, in its turn, on two things: first, the magnitude of the threatened evil, and second, the probability of it. The greater the evil is, and the nearer it is, the greater is the indifference or carelessness of him who creates the danger.
Inasmuch, therefore, as carelessness varies in degree, it is necessary to know what degree of it is requisite to constitute culpable negligence. What measure of care does the law demand? What amount of anxious consideration for the interests of others is a legal duty, and within what limits is indifference lawful?
We have first to notice a possible standard of care which the law might have adopted but has not. It does not demand the highest degree of care of which human nature is capable. I am not liable for harm ignorantly done by me, merely because by some conceivable exercise of prudential foresight I might have anticipated the event and so avoided it. Nor am I liable because, knowing the possibility of harm, I fail to take every possible precaution against it. The law demands not that which is possible, but that which is reasonable in view of the magnitude of the risk. Were men to act on any other principle than this, excess of caution would paralyse the business of the world. The law, therefore, allows every man to expose his fellows to a certain measure of risk, and to do so even with full knowledge. If an explosion occurs in my powder mill, I am not liable for negligence, even though I established and carried on the industry with full knowledge of its dangerous character. This is a degree of indifference to the safety of other men’s lives and property which the law deems permissible because not excessive. Inasmuch as the carrying of firearms and the driving of horses are known to be the occasions of frequent harm, extreme care and the most scrupulous anxiety as to the interests of others would prompt a man to abstain from those dangerous forms of activity. Yet it is expedient in the public interest that those activities should go on, and therefore that men should be exposed to the incidental risks of them. Consequently the law does not insist on any standard of care which would include them within the limits of culpable negligence. It is for the law to draw the line as best it can, so that while prohibiting unreasonable carelessness, it does not at the same time demand unreasonable care.
What standard, then, does the law actually adopt? It demands the amount of care which would be shown in the circumstances of the particular case by an ordinarily careful man. It is content to adopt the standard which is customary for the time being in the community. It is satisfied with conduct which in point of carefulness conforms to the moral standard and the ordinary practice of mankind. Less than this is not sufficient, and more than this is not required. A jury in determining the question of negligence will decide whether in their opinion the defendant acted with reasonable care; and in so doing they represent and express the current opinion and practice of the community as to the risks to which one man is justified in exposing others, and as to the degree of consideration for the welfare of others which the community exacts and commonly receives from its members.
The standard thus adopted by the law is of necessity somewhat vague and indeterminate. It is not practicable to any great extent to lay down any more definite and detailed rules as to what classes of acts are negligent and what are not. Too much depends upon the circumstances of the individual case, and the standard of due care is too liable to alter with the advance of knowledge and the changes of social life and manners. Risks which were once deemed excessive may become permissible in view of the increasing stress and hurry of modern life, and conversely conduct which to-day is beyond reproach may in the future become grossly negligent by reason of the growth of skill or knowledge.
Nevertheless, here as elsewhere, the law seeks for definite and specific principles. It dislikes the licence of the arbitrium judicis. So far as practicable and justifiable it desires to make negligence a matter not of fact but of legal rule and definition. It seeks to supersede the vague principle that that is negligence which a jury considers such, by substituting for it a body of legal doctrine determining the boundaries of negligence in specific instances. This, however, is possible only to a very limited extent. It would seem, indeed, that all legal rules on this matter are merely negative, determining what does not amount to negligence, and never positive, determining that certain acts are negligent in law. It has been decided as a matter of law, for example, that it is not negligent to drive cattle through the streets of a town loose instead of leading them with halters.366 Nor is it negligent to allow a dog to run at large, if the owner has no actual knowledge of its vicious temper. Nor is it negligent to try a horse for the first time in a frequented thoroughfare.367 Nor is there any negligence in the usual practice of railway servants in violently shutting the doors of railway carriages without warning,368 notwithstanding the risk of injury to the hands of passengers.369
As has been already indicated, there seem to be no corresponding rules to the effect that certain kinds of conduct are negligent in law. The law never goes further in this direction than to say that certain facts are sufficient evidence of negligence, that is to say, are sufficient to entitle the jury to find negligence as a matter of fact if they think fit. The reason for this cautious attitude of the law is obvious. No facts can be such cogent proof of negligence that the law may safely and wisely take them as conclusive. For they may be capable of explanation by other facts, and that which is apparently due to the most culpable negligence may be due in reality to inevitable mistake or accident. Thus the law does not contain any rule to the effect that driving on the wrong side of the road amounts to negligence. The rule is merely that such conduct is evidence of negligence.370 Nor is the act of leaving a horse and cart unattended in the street an act of negligence in law; it is merely one from which a jury is at liberty to infer negligence in fact.371