To illustrate these observations let us briefly analyze the physical principles of our actions. When an object strikes any of our senses, and the sensation it produces is agreeable, it creates a desire, which desire must have a relation to some of our qualities or modes of enjoyment. The object we cannot desire but either to see, taste, hear, smell, or to touch. We desire it merely that we may render the first sensation still more agreeable, or to excite another which is a new manner of enjoying the object; for if in the moment that we perceive an object we could enjoy it fully, through all the senses at once, we should have nothing to desire. The source of desire, then, is our being badly situated with respect to the object perceived, our being either too far from, or too near to it. This being the case we naturally change our situation, because at the same time that we perceive the object, we likewise perceive the cause which prevents our obtaining a full enjoyment of it. From the impression which the object produces upon our senses, then, the motion we make in consequence of that desire, and the desire itself, solely proceeds. An object we perceive by the eye, and which we desire to touch, if within our reach, we stretch forth our hands, and if at a distance we put ourselves in motion to approach it. A man deeply immersed in thought, if he is hungry, and there is a piece of bread before him, he will seize it, and even carry it to his mouth and eat it, without being conscious that he has done so. These movements are a necessary consequence of the first impressions of objects, and would never fail to succeed this impression if other intervening impressions did not often oppose this natural effect, either by weakening or by destroying the action of the first. An organized being void of sensation, as an oyster, whose sense of feeling is probably very imperfect, is deprived not only of progressive motion, but even of sentiment and intelligence, as either of these would produce desire, which would manifest itself by exterior movement. That such beings are divested of a sense of their own existence I will not assert, but at least that sense must be very imperfect, since they have no perception of the existence of others. It is the action of objects upon the senses which creates desire, and desire progressive motion. In order to render this truth still more sensible, let us suppose a man, at the instant his will incites him to approach an object, suddenly deprived of all his members, his body reduced to a physical point, to a globular atom, and, provided the desire still subsists, he will exert his whole strength in order to change his situation. The exterior and progressive movement depends not, then, upon the organization and figure of the body and members, since whatever be the conformation any of being it will not fail to move, provided it has senses, and a desire to gratify them.