Each being, by its essence, by its peculiar nature, has the faculty of producing, is capable of receiving, has the power of communicating, a variety of motion. Thus some beings are proper to strike our organs; these organs are competent to receiving the impression, are adequate to undergoing changes by their presence. Those which cannot act on any of our organs, either immediately and by themselves, or immediately by the intervention of other bodies, exist not for us; since they can neither move us, nor consequently furnish us with ideas: they can neither be known to us, nor of course be judged of by us. To know an object, is to have felt it; to feel it, it is requisite to have been moved by it. To see, is to have been moved, by something acting on the visual organs; to hear, is to have been struck, by something on our auditory nerves. In short, in whatever mode a body may act upon us, whatever impulse we may receive from it, we can have no other knowledge of it than by the change it produces in us.
Nature, as we have already said, is the assemblage of all the beings, consequently of all the motion of which we have a knowledge, as well as of many others of which we know nothing, because they have not yet become accessible to our senses. From the continual action and re-action of these beings, result a series of causes and effects; or a chain of motion guided by the constant and invariable laws peculiar to each being; which are necessary or inherent to its particular nature—which make it always act or move after a determinate manner. The different principles of this motion are unknown to us, because we are in many instances, if not in all, ignorant of what constitutes the essence of beings. The element
