It can be only by the diversity of impressions and effects, which bodies make upon us, that we feel them; that we have perceptions and ideas of them; that we distinguish one from another; that we assign them properties. Now, to see or feel an object, the object must act upon our organs; this object cannot act upon us, without exciting some motion in us; it cannot excite motion in us, if it be not in motion itself. At the instant I see an object, my eyes are struck by it; I can have no conception of light and vision, without motion, communicated to my eye, from the luminous, extended, coloured body. At the instant I smell something, my sense is irritated, or put in motion, by the parts that exhale from the odoriferous body. At the moment I hear a sound, the tympanum of my ear is struck by the air, put in motion by a sonorous body, which would not act if it were not in motion itself. Whence it evidently follows, that, without motion, I can neither feel, see, distinguish, compare, judge, nor occupy my thoughts upon any subject whatever.

We are taught, that the essence of a thing is that from which all its properties flow. Now, it is evident, that all the properties of bodies, of which we have ideas, are owing to motion, which alone informs us of their existence, and gives us the first conceptions of them. I cannot be informed of my own existence but by the motions I experience in myself. I am therefore forced to conclude, that motion is as essential to matter as extension, and that matter cannot be conceived without it.

Should any person deny, that motion is essential and necessary to matter; they cannot, at least, help acknowledging that bodies, which seem dead and inert, produce motion of themselves, when placed in a fit situation to act upon one another. For instance; phosphorus, when exposed to the air, immediately takes fire. Meal and water, when mixed, ferment. Thus dead matter begets motion of itself. Matter has then the power of self-motion; and nature, to act, has no need of a mover, whose pretended essence would hinder him from acting.