How the Mind and Body Act on each other, and how one Body moves another

Abstract

I think most people would not believe me if I said that it is no more difficult to conceive how the human mind, without being extended, can move the body and how the body without being a spiritual thing can act on the mind, than to conceive how a body has the power to move itself and to communicate its motion to another body. Yet there is nothing more true, and that is what I propose to show in this chapter. But, I will be told, is it not clear and evident that heavy things move downwards, that light things rise upwards, and that bodies communicate their motion to one another? I agree, but there is a big difference between the obviousness of the effect and that of the cause. The effect is very clear here, for what do our senses show us more clearly than the various movements of bodies? But do they show us the force which carries heavy things downwards, light things upwards, and how one body has the power to make another body move? Do our senses teach us how motion can pass from one body to another, why only part of the motion passes from one to another, and why a body cannot communicate its motion, as a teacher communicates their knowledge, without losing any of what it gives? The cause of the motion of bodies is not therefore something which is as obvious as one might think, and that is why I said at the beginning that it was no more difficult to conceive how the mind moves the body than to know how one body moves another because, in fact, one must have recourse to the same universal cause in both cases. Since this is the most important point, it is necessary to speak about it here to remove from many people’s minds the unfortunate tendency to believe that unless their soul were corporeal, it would not have the power to move the body because, they say, it could not do so without touching it and, according to the words of the poet, ‘Nothing except a body can touch or be touchedi’ ¹⁵⁴ — as if motion could be communicated only by impact or as if it were as easy to perceive how one body could move another as it is to see how it touches it.