§ 148 Accident
Unlike mistake, inevitable accident is commonly recognised by our law as a ground of exemption from liability. It is needful, therefore, to distinguish accurately between these two things, for they are near of kin. Every act which is not done intentionally is done either accidentally or by mistake. It is done accidentally, when it is unintentional in respect of its consequences. It is done by mistake, when it is intentional in respect of its consequences, but unintentional in respect of some material circumstance. If I drive over a man in the dark because I do not know that he is in the road, I injure him accidentally; but if I procure his arrest, because I mistake him for some one who is liable to arrest, I injure him not accidentally but by mistake. In the former case I did not intend the harm at all, while in the latter case I fully intended it, but falsely believed in the existence of a circumstance which would have served to justify it. So if by insufficient care I allow my cattle to escape into my neighbour’s field, their presence there is due to accident; but if I put them there because I wrongly believe that the field is mine, their presence is due to mistake. In neither case did I intend to wrong my neighbour, but in the one case my intention failed as to the consequence, and in the other as to the circumstance.
Accident, like mistake, is either culpable or inevitable. It is culpable when due to negligence, but inevitable when the avoidance of it would have required a degree of care exceeding the standard demanded by the law. Culpable accident is no defence, save in those exceptional cases in which wrongful intent is the exclusive and necessary ground of liability. Inevitable accident is commonly a good defence, both in the civil and in the criminal law.
To this rule, however, there are, at least in the civil law, important exceptions. These are cases in which the law insists that a man shall act at his peril, and shall take his chance of accidents happening. If he desires to keep wild beasts,387 or to light fires,388 or to construct a reservoir of water,389 or to accumulate upon his land any substance which will do damage to his neighbours if it escapes,390 or to erect dangerous structures by which passengers in the highway may come to harm,390 he will do all these things suo periculo (though none of them are per se wrongful) and will answer for all ensuing damage notwithstanding consummate care.
There is one case of absolute liability for accident which deserves special notice by reason of its historical origin. Every man is absolutely responsible for the trespasses of his cattle. If my horse or my ox escapes from my land to that of another man, I am answerable for it without any proof of negligence.391 Such a rule may probably be justified as based on a reasonable presumption of law that all such trespasses are the outcome of negligent keeping. Viewed historically, however, the rule is worth notice as one of the last relics of the ancient principle that a man is answerable for all damage done by his property. In the theory of ancient law I am liable for the trespasses of my cattle, not because of my negligent keeping of them, but because of my ownership of them. For the same reason in Roman law a master was liable for the offences of his slaves. The case is really, in its historical origin, one of vicarious liability. In early law and custom vengeance, and its products responsibility and punishment, were not conceived as necessarily limited to human beings, but were in certain cases extended to dumb animals and even inanimate objects. We have already cited in another connection the provision of the Mosaic law that “If an ox gore a man or a woman that they die, then the ox shall be surely stoned and his flesh shall not be eaten.”392 In the Laws of Plato it is said:393 “If a beast of burden or other animal cause the death of any one... the kinsman of the deceased shall prosecute the slayer for murder, and the wardens of the country... shall try the cause; and let the beast when condemned be slain by them, and cast beyond the borders.” So in the Laws of King Alfred:394 “If at their common work,” (of wood cutting) “one man slay another unwilfully, let the tree be given to the kindred.” And by English law until the year 1846 the weapon or other thing which “moved to the death of a man” was forfeited to the King as guilty and accursed.395 Here we have the ground of a rule of absolute liability. If a man’s cattle or his slaves do damage, they are thereby exposed to the vengeance of the injured person. But to take destructive vengeance upon them is to impose a penalty upon their owner. The liability thence resulting probably passed through three stages: first, that of unconditional forfeiture or surrender of the property to the vengeance of the injured person; secondly, that of an option given to the owner between forfeiture and redemption—the actiones noxales of Roman law;396 and thirdly, that of compulsory redemption, or in other words, unconditional compensation.