_B._ You are to draw from these definitions, and from whatsoever truth else you know by the light of nature, such general consequences as may serve for axioms, or principles of your ratiocination. _A._ That is hard to do. _B._ I will draw them myself, as many as for our present discourse of natural causes we shall have need of; so that your part will be no more than to take heed I do not deceive you. _A._ I will look to that. _B._ My first axiom then shall be this: Two bodies, at the same time, cannot be in one place. _A._ That is true: for we number bodies as we fancy them distinct, and distinguish them by their places. You may therefore add: nor one body at the same time in two places. And philosophers mean the same, when they say: there is no penetration of bodies. _B._ But they understand not their own words: for penetration signifies it not. My second axiom is, that nothing can begin, change, or put an end to, its own motion. For supposing it begin just now, or being now in motion, change its way or stop; I require the cause why now rather than before or after, having all that is necessary to such motion, change, or rest, alike at all times? _A._ I do not doubt but the argument is good in bodies inanimate; but perhaps in voluntary agents it does not hold. _B._ How it holds in voluntary agents we will then consider when our method hath brought us to the powers and passions of the mind. A third axiom shall be this: whatsoever body being at rest is afterwards moved, hath for its immediate movement some other body which is in motion and toucheth it. For, since nothing can move itself, the movent must be external. And because motion is change of place, the movent must put it from its place, which it cannot do till it touch it. _A._ That is manifest, and that it must more than touch it; it must also follow it. And if more parts of the body are moved than are by the movent touched, the movent is not immediate. And by this reason, a continued body, though never so great, if the first superficies be pressed never so little back, the motion will proceed through it. _B._ Do you think that to be impossible? I will prove it from your own words: for you say that the movent does then touch the body which it moveth. Therefore it puts it back; but that which is put back, puts back the next behind, and that again the next; and so onward to any distance, the body being continued. The same is also manifest by experience, seeing one that walks with a staff can distinguish, though blind, between stone and glass; which were impossible, if the parts of his staff between the ground and his hand made no resistance. So also he that in the silence of the night lays his ear to the ground, shall hear the treading of men’s feet farther than if he stood upright.