Whenever we judge that a thing is good as a means, we are making a judgment with regard to its causal relations: we judge both that it will have a particular kind of effect, and that that effect will be good in itself. But to find causal judgments that are universally true is notoriously a matter of extreme difficulty. The late date at which most of the physical sciences became exact, and the comparative fewness of the laws which they have succeeded in establishing even now, are sufficient proofs of this difficulty. With regard, then, to what are the most frequent objects of ethical judgments, namely actions, it is obvious that we cannot be satisfied that any of our universal causal judgments are true, even in the sense in which scientific laws are so. We cannot even discover hypothetical laws of the form Exactly this action will always, under these conditions, produce exactly that effect. But for a correct ethical judgment with regard to the effects of certain actions we require more than this in two respects. (1) We require to know that a given action will produce a certain effect, under whatever circumstances it occurs. But this is certainly impossible. It is certain that in different circumstances the same action may produce effects that are utterly different in all respects upon which the value of the effects depends. Hence we can never be entitled to more than a generalisation—to a proposition of the form This result generally follows this kind of action; and even this generalisation will only be true, if the circumstances under which the action occurs are generally the same. This is in fact the case, to a great extent, within any one particular age and state of society. But, when we take other ages into account, in many most important cases the normal circumstances of a given kind of action will be so different, that the generalisation which is true for one will not be true for another. With regard then to ethical judgments which assert that a certain kind of action is good as a means to a certain kind of effect, none will be universally true; and many, though generally true at one period, will be generally false at others. But (2) we require to know not only that one good effect will be produced, but that, among all subsequent events affected by the action in question, the balance of good will be greater than if any other possible action had been performed. In other words, to judge that an action is generally a means to good is to judge not only that it generally does some good, but that it generally does the greatest good of which the circumstances admit. In this respect ethical judgments about the effects of action involve a difficulty and a complication far greater than that involved in the establishment of scientific laws. For the latter we need only consider a single effect; for the former it is essential to consider not only this, but the effects of that effect, and so on as far as our view into the future can reach. It is, indeed, obvious that our view can never reach far enough for us to be certain that any action will produce the best possible effects. We must be content, if the greatest possible balance of good seems to be produced within a limited period. But it is important to notice that the whole series of effects within a period of considerable length is actually taken account of in our common judgments that an action is good as a means; and that hence this additional complication, which makes ethical generalisations so far more difficult to establish than scientific laws, is one which is involved in actual ethical discussions, and is of practical importance. The commonest rules of conduct involve such considerations as the balancing of future bad health against immediate gains; and even if we can never settle with any certainty how we shall secure the greatest possible total of good, we try at least to assure ourselves that probable future evils will not be greater than the immediate good. (§ 16 ¶ 1)