There are kinds of cases, on the other hand, in which the law, without aid from legislation, has imposed on occupiers and other persons in analogous positions a duty stricter than that of being answerable for themselves and their servants. Duties of this kind have been called "duties of insuring safety." Generally they extend to having the building, structure, or works in such order, having regard to the nature of the case, as not to create any unusual danger to persons lawfully frequenting, using or passing by them, which the occupier knows or ought to know and could prevent by reasonable care ; but in some cases of "extra-hazard ous" risk, even proof of all possible diligence—according to English authority, which is not unanimously accepted in America —will not suffice.
Flood, and the later decision of the House of Lords in Quinn v. Leatteem (1901, A.C. 495), this view has ceased to be tenable. The ground of action is the intentional violation of an existing legal right ; which, however, since 1906, may be practised with impunity in Great Britain "in contemplation or furtherance of a trade dispute": Trade Disputes Act, sec. 3. It must be remem bered, however, that the presence or absence of personal ill will, and the behaviour of the parties generally, may have an important effect, when liability is proved or admitted, in mitigating or aggra vating the amount of damages awarded.
We have already had to mention the existence of grounds of immunity for acts that would otherwise be wrongful. Such grounds there must be if the law is to be enforced and justice administered at all, and if the business of life is to be carried on with any freedom. Roughly speaking, we find in these cases one of the following conditions: Either the defendant was executing a lawful authority; or he was justified by extraordinary necessity; or he was doing something permitted by legislation for reasons of superior utility, though it may produce damage to others, and either with or without special provisions for compensating dam age ; or he was exercising a common right in matters open to free use and competition; or the plaintiff had, by consent or otherwise, disabled himself from having any grievance.
As Justice Holmes of the Supreme Court of the United States has said, we allow unlimited trade competition (so long as it is without fraud) though we know that many traders must suffer, and some may be ruined by it, because we hold that free com petition is worth more to society than its costs. A State with different economic foundations might have a different law on this, as on many other points. This freedom extends not only to the exercise of one's calling, but to choosing with whom and under what conditions one will exercise it. Also the law will not enquire with what motives a common right is exercised; and this applies to the ordinary rights of an owner in the use of his property as well as to the right of every man to carry on his business. The rule that a man's motives for exercising his common rights are not examinable involves the consequence that advising or pro curing another, who is a free agent, to do an act of this kind can, a fortiori, not be an actionable wrong at the suit of a third per son who is damnified by the act, and that whatever the adviser's motives may be. This appears to be included in the decision of the House of Lords in Allen v. Flood. That decision, though not binding in any American court, is approved and followed in most American jurisdictions. It is otherwise where a system of coercion is exercised on a man's workmen or customers in order to injure him in his business. The extension of immunity to such conduct would destroy the value of the common right which the law pro tects: Quinn v. Leathem.