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152 them, it may thus tell us which of the alternatives, among which we can choose, it is best to choose. If it could do this it would be sufficient for practical guidance.

93. But (3) it is plain that even this is a task of immense difficulty. It is difficult to see how we can establish even a probability that by doing one thing we shall obtain a better total result than by doing another. I shall merely endeavour to point out how much is assumed, when we assume that there is such a probability, and on what lines it seems possible that this assumption may be justified—that no sufficient reason has ever yet been found for considering one action more right or more wrong than another.

(a) The first difficulty in the way of establishing a probability that one course of action will give a better total result than another, lies in the fact that we have to take account of the effects of both throughout an infinite future. We have no certainty but that, if we do one action now, the Universe will, throughout all time, differ in some way from what it would have been, if we had done another; and, if there is such a permanent difference, it is certainly relevant to our calculation. But it is quite certain that our causal knowledge is utterly insufficient to tell us what different effects will probably result from two different actions, except within a comparatively short space of time; we can certainly only pretend to calculate the effects of actions within what may be called an ‘immediate’ future. No one, when he proceeds upon what he considers a rational consideration of effects, would guide his choice by any forecast that went beyond a few centuries at most; and, in general, we consider that we have acted rationally, if we think we have secured a balance of good within a few years or months or days. Yet, if a choice guided by such considerations is to be rational, we must certainly have some reason to believe that no consequences of our action in a further future will generally be such as to reverse the balance of good that is probable in the future which we can forsee. This large postulate must be made, if we are ever to assert that the results of one