single one, to have obtained even a hypothetical universal law, such as has been obtained in the exact sciences. We cannot even say: If this action is performed, under exactly these circumstances, and if no others interfere, this important effect, at least, will always be produced. But, in the second place, an ethical law is not merely hypothetical. If we are to know that it will always be better to act in a certain way, under certain circumstances, we must know not merely wha effects such actions will produce, provided no other circumstances interfere, but also that no other circumstances will interfere. And this it is obviouisly impossible to know with more than probability. An ethical law has the nature not of a scientific law but of a scientific prediction: and the latter is always merely probable, although the probability may be very great. An engineer is entitled to assert that, if a bridge be built in a certain way, it will probably bear certain loads for a certain time; but he can never be absolutely certain that it has been built in the way required, nor that, even if it has, some accident will not intervene to falsify his prediction. With any ethical law, the same must be the case; it can be no more than a generalisation: and here, owing to the comparative absence of accurate hypothetical knowledge, on which the prediction should be based, the probability is comparatively small. But finally, for an ethical generalisation, we require to know not only what effects will be produced, but also what are the comparative values of those effects; and on this question too, it must be admitted, considering what a prevalent opinion Hedonism has been, that we are very likely to be mistaken. It is plain, then, that we are not soon likely to know more than that one kind of action will generally produce better effects than another; and that more than this has certainly never been proved. In no two cases will all the effects of any kind of action be precisely the same, because in each case some of the circumstances will differ; and although the effects, that are important for good or evil, may be generally the same, it is extremely unlikely that they will always be so.
95. (c) If, now, we confine ourselves to a search for actions which are generally better as means than any probable alter-
