The beings of the human species, as well as all other beings, are susceptible of two sorts of motion: the one, that of the mass, by which an entire body, or some of its parts, are visibly transferred from one place to another; the other, internal and concealed, of some of which man is sensible, while some takes place without his knowledge, and is not even to be guessed at, but by the effect it outwardly produces. In a machine so extremely complex as man, formed by the combination of such a multiplicity of matter, so diversified in its properties, so different in its proportions, so varied in its modes of action, the motion necessarily becomes of the most complicated kind; its dullness, as well as its rapidity, frequently escapes the observation of those themselves, in whom it takes place. Let us not, then, be surprised, if, when man would account to himself for his existence, for his manner of acting, finding so many obstacles to encounter, he invented such strange hypotheses to explain the concealed spring of his machine--if then this motion appeared to him, to be different from that of other bodies, he conceived an idea, that he moved and acted in a manner altogether distinct from the other beings in Nature. He clearly perceived that his body, as well as different parts of it, did act; but, frequently, he was unable to discover what brought them into action: from whence he received the impulse: he then conjectured he contained within himself a moving principle distinguished from his machine, which secretly gave an impulse to the springs which set this machine in motion; that moved him by its own natural energy; that consequently he acted according to laws totally distinct from those which regulated the motion of other beings: he was conscious of certain internal motion, which he could not help feeling; but how could he conceive, that this invisible motion was so frequently competent to produce such striking effects? How could he comprehend, that a fugitive idea, an imperceptible act of thought, was so frequently capacitated to bring his whole being into trouble and confusion? He fell into the belief, that he perceived within himself a substance distinguished from that self, endowed with a secret force; in which he supposed existed qualities distinctly differing from those, of either the visible causes that acted on his organs, or those organs themselves. He did not sufficiently understand, that the primitive cause which makes a stone fall, or his arm move, are perhaps as difficult of comprehension, as arduous to be explained, as those internal impulses, of which his thought or his will are the effects. Thus, for want of meditating Nature--of considering her under her true point of view--of remarking the conformity--of noticing the simultaneity, the unity of the motion of this fancied motive-power with that of his body--of his material organs--he conjectured he was not only a distinct being, but that he was