movement of thought: the essence of body is conditioned through this thought, that is, it is not true essence. Descartes now makes his way from the Notion of extension to the laws of motion, as the universal knowledge of the corporeal in its implicitude; he shows (α) that there is no vacuum, for that would be an extension without bodily substance, _i.e._ a body without body; (β) that there are no atoms (no indivisible independent existence), for the same reason, viz., because the essence of body is extension. (γ) He further shows that a body is set in motion by something outside of it, but of itself it continues in a condition of rest, and likewise it must, when in a condition of movement, be brought to rest by another outside of it—this is the property of inertia.[186] These are unmeaning propositions, for an abstraction is involved for instance in asserting simple rest and movement in their opposition. Extension and motion are the fundamental conceptions in mechanical physics; they represent the truth of the corporeal world. It is thus that ideality comes before the mind of Descartes, and he is far elevated above the reality of the sensuous qualities, although he does not reach so far as to the separation of this ideality. He thus remains at the point of view of mechanism pure and simple. Give me matter (extension) and motion and I will build worlds for you, is what Descartes virtually says.[187] Space and time were hence to him the only determinations of the material universe. In this, then, lies the mechanical fashion of viewing nature, or the natural philosophy of Descartes is seen to be purely mechanical.[188] Hence changes in matter are due merely to motion, so that Descartes traces every relationship to the rest and movement of particles, and all material diversity such as colour, and taste—in short, all bodily qualities and animal phenomena—to mechanism. In living beings processes such as that of digestion are mechanical effects which have as principles, rest and movement. We here see the ground and origin of the mechanical philosophy; but further on we find that this is unsatisfactory, for matter and motion do not suffice to explain life. Yet the great matter in all this is that thought goes forward in its determinations, and that it constitutes from these thought-determinations the truth of nature. In his consideration of the system of the world and the movement of the heavenly bodies, Descartes has worked out the mechanical view more fully. He thus comes to speak of the earth, the sun, &c., and of his conception of the circling motion of the heavenly bodies in the form of vortices: of metaphysical hypotheses as to how small particles pass into, out of, and through pores and act on one another; and finally to saltpetre and gunpowder.[189]