XII. There is not and cannot be vacuum of any kind.
XIII. The idea of space is the idea of extension in the abstract.
XIV. The imagination of an unlimited space is only an attempt of the imagination to follow the understanding in the abstraction of extension. It also arises from our habit of seeing through transparent mediums, and moving in fluids whose resistance is not perceptible.
XV. As all that we know of bodies is, that they are extended and affect us, whatever has these two conditions is to us a body.
XVI. But as we do not know the essence of bodies, we do not know whether a body can exist without extension.
XVII. Neither do we know what modifications the extension of one body may be subject to, with respect to others.
XVIII. The elements of which bodies are composed are unknown to us.
XIX. The approximation of some bodies to others, and the gravitation which results from it, seem to be the necessary effect of their present relations.
XX. The necessity of approximation does not suffice to explain the laws of motion, or their beginning, or their continuation.