begin by asking what is the process of Science in dealing with all questions of causation, we find that this process when reduced to its simplest elements always consists in referring every event as an effect to some cause which we know or believe to have produced some other and similar event. Newton is struck by a falling apple. His first thought is, 'how hard the blow.' His second is wonder, 'how far the earth's attraction, which has caused this hard blow, extends.' His third, 'why not as far as the moon?' And he proceeds to assign the motion of the moon to the same cause as that which produced the motion of the apple. Taking this as a working hypothesis, he examines what would be the motions of all the planets if this were true. And the examination ends with establishing the high probability of the Law of Gravitation.

Now this being the invariable process of Science, it follows that our conception of cause must come originally from that cause which we have within ourselves and with which we cannot but begin, the action of the human will. It is from this action that is obtained that conception which underlies the ordinary conception of cause, namely, that of force or power.

This conception of force or power is derived from the consciousness of our own power to move our limbs, and perhaps too of passions, temptations, sentiments to move or oppose our wills. This power is most distinctly felt when it is resisted. The effort which is necessary when we choose to do what we have barely strength to do, impresses on us more clearly the sense of a force residing in ourselves capable of overcoming resistance. Having the power to move our limbs, and that too against some resistance, we explain, and in no other way can we explain, other motions by the supposition of a similar power. In so doing we are following strictly the scientific instinct and the scientific process. We are putting into the same class the motions that we observe in other things and the motions that we observe in ourselves; the latter are due to acts of our own wills, the former are assigned to similar acts of other wills. Hence in infancy, and in the infancy of mankind, the whole world is peopled with persons because everything that we observe to move is personified. A secret will moves the wind, the sun, the moon, the stars, and each is independent of the others.

Soon a distinction grows up between the things that seem to have a spontaneous motion and those that have not, and spontaneous motion is taken as the sign of life. And all inanimate things, of whatever kind, are held to be moved, if they move at all, by a force outside themselves. Their own force is limited to that of resisting, and does not include that of originating motion. But though they cannot originate motion they are observed to be capable of transmitting it. And the notion of force is expanded by the recognition that it can be communicated from one thing to another and yet to another, and that we may have to go back many steps before we arrive at the will from which it originated. We began with the notion of a power the action of which was or appeared to be self-originated: we come to the notion of a power the action of which is nothing more than the continuance of preceding action. And the special characteristic of the action of this force as thus conceived, which we may call the derivative force, is seen to be its regularity, just as the special characteristic of the self-originating action was its spontaneity.

As experience increases the regularity of the action of the derivative force is more and more observable, and then arises the notion of a law or rule regulating the action of every such force. And a perpetually increasing number of phenomena are brought under this head, and are shown to be, not the immediate results of self-originating action, but the more or less remote results of derivative action governed by laws. And even a large number of those phenomena, which specially belong to life and living creatures, in whom alone, if anywhere, the self-originating action is to be found, are observed to be subject to law and therefore to be the issue not of self-originating but of derivative action. And this observed regularity it is found possible to trace much more widely than it is possible to trace any clear evidence of what we understand by force. And so, at last, we frequently use the word force as it were by anticipation, not to express the cause of the phenomena, which indeed we do not yet know, but as a convenient abbreviation for a large number of facts classed under one head. And this it is which enables Hume to maintain that we mean no more by a cause than an event which is invariably followed by another event. We discover invariability much faster than we can discover causation; and having discovered invariability in any given case, we presume causation even when we cannot yet show it, and use language in accordance with that presumption. Thus, for instance, we speak of the force of gravitation, although we cannot yet prove that there is any such force, and all that we know is that material particles move as if such a force were acting on them.

As Science advances it is seen that the regularity of phenomena is far more important to us than their causes. And the attention of all students of Nature is fixed on that rather than on causation. And this regularity is seen to be more and more widely pervading all phenomena of every class, until the mind is forced to conceive the possibility that it may be absolutely universal, and that even will itself may come within its supreme dominion.

But to the very last the idea of causation retains the traces of its origin. For in the first place every step in this building up of science assumes a permanence underlying all phenomena. We cannot believe that the future will be like the past except because we believe that there is something permanent which was in the past and will be in the future. And this assumption of something permanent in things around us comes from the consciousness of something permanent within us. We know our own permanence. Whatever else we know or do not know about ourselves, we are sure of our own personal identity through successive periods of life. And as our explanation of things outside begins by classing them with things inside we still continue to ascribe permanence to whatever underlies phenomena even when we have long ceased to ascribe individual wills to any except beings like ourselves. And without this assumption of permanence our whole science would come to the ground.

And in the second place let it be remembered that we began with the will causing the motions of the limbs. Now there is, as far as we know, no other power in us to affect external nature than by setting something in motion. We can move our limbs, and by so doing move other things, and by so doing avail ourselves of the laws of Nature to produce remoter effects. But, except by originating motion, we cannot act at all. And, accordingly, throughout all science the attempt is made to reduce all phenomena to motions. Sounds, colours, heat, chemical action, electricity, we are perpetually endeavouring to reduce to vibrations or undulations, that is, to motion of some sort or other. The mind seems to find a satisfaction when a change of whatever kind is shown to be, or possibly to be, the result of movement. And so too all laws of Nature are then felt to be satisfactorily explained when they can be traced to some force exhibited in the movement of material particles. The law of Gravitation has an enormous evidence in support of it considered simply as a fact. And yet how many attempts have been made to represent it as the result of vortices or of particles streaming in all directions and pressing any two bodies together that lie in their path! The facts which establish it are enough. Why then these attempts? What is felt to be yet wanting? What is felt to be wanting is something to show that it