(_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 foresee. This large postulate must be made, if we are ever to assert that the results of one action will be even probably better than those of another. Our utter ignorance of the far future gives us no justification for saying that it is even probably right to choose the greater good within the region over which a probable forecast may extend. We do, then, assume that it is improbable that effects, after a certain time, will, in general, be such as to reverse the comparative value of the alternative results within that time. And that this assumption is justified must be shewn before we can claim to have given any reason whatever for acting in one way rather than in another. It may, perhaps, be justified by some such considerations as the following. As we proceed further and further from the time at which alternative actions are open to us, the events of which either action would be part cause become increasingly dependent on those other circumstances, which are the same, whichever action we adopt. The effects of any individual action seem, after a sufficient space of time, to be found only in trifling modifications spread over a very wide area, whereas its immediate effects consist in some prominent modification of a comparatively narrow area. Since, however, most of the things which have any great importance for good or evil are things of this prominent kind, there may be a probability that after a certain time all the effects of any particular action become so nearly indifferent, that any difference between their value and that