[79] The business of the law of torts is to fix the dividing lines between those cases in which a man is liable for harm which he has done, and those in which he is not. But it cannot enable him to predict with certainty whether a given act under given circumstances will make him liable, because an act will rarely have that effect unless followed by damage, and for the most part, if not always, the consequences of an act are not known, but only guessed at as more or less probable. All the rules that the law can lay down beforehand are rules for determining the conduct which will be followed by liability if it is followed by harm--that is, the conduct which a man pursues at his peril. The only guide for the future to be drawn from a decision against a defendant in an action of tort is that similar acts, under circumstances which cannot be distinguished except by the result from those of the defendant, are done at the peril of the actor; that if he escapes liability, it is simply because by good fortune no harm comes of his conduct in the particular event. If, therefore, there is any common ground for all liability in tort, we shall best find it by eliminating the event as it actually turns out, and by considering only the principles on which the peril of his conduct is thrown upon the actor. We are to ask what are the elements, on the defendant's side, which must all be present before liability is possible, and the presence of which will commonly make him liable if damage follows. The law of torts abounds in moral phraseology. It has much to say of wrongs, of malice, fraud, intent, and negligence. Hence it may naturally be supposed that the risk of a man's conduct is thrown upon him as the result of some moral short-coming. But while this notion has been [80] entertained, the extreme opposite will be found to have been a far more popular opinion;--I mean the notion that a man is answerable for all the consequences of his acts, or, in other words, that he acts at his peril always, and wholly irrespective of the state of his consciousness upon the matter. To test the former opinion it would be natural to take up successively the several words, such as negligence and intent, which in the language of morals designate various well-understood states of mind, and to show their significance in the law. To test the latter, it would perhaps be more convenient to consider it under the head of the several forms of action. So many of our authorities are decisions under one or another of these forms, that it will not be safe to neglect them, at least in the first instance; and a compromise between the two modes of approaching the subject may be reached by beginning with the action of trespass and the notion of negligence together, leaving wrongs which are defined as intentional for the next Lecture.