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In Descartes cosmology, the universe is essentially mechanical in character. Copernican heliocentrism is accepted, and planetary motion is explained in terms of a swirling '''vortex''' of material particles around the central sun. Earth, as a moving planet, is the center of its own smaller vortex. The particles of the vortex push larger bodies towards its center and this explains gravity without supposing, as did Aristotle, that the sphere of earth was at rest in its natural place; the center of the universe. It also made it reasonable to suppose that other planets had their own attractive vorticies, and were thus other worlds. [[CiteRef::Garber (1992)]]

Descartes also challenged Aristotelian physiology. Aristotle's theory of physiology posited three souls or vital principles; the nutritive soul, responsible for nutrition and reproduction, comprised the entirety of the soul in plants. The sensitive soul, responsible for perception, locomotion, imagination, and desire, was added to the sensitive soul in animals. A third component, the intellectual soul, was found uniquely in human beings. [[CiteRef::Shields (2016b)]][[CiteRef::Van der Eijk (2000)]] Descartes rejected the nutritive and sensitive souls, supposing their functions were instead performed by corpuscular mechanisms, the nature of which he outlined in his ''Treatise on Man''. [[CiteRef::Descartes (2007)]] Descartes' mental substance served roughly the same role as Aristotle's intellectual soul. Animals, according to Descartes, are complex automata composed of physical substance only and cannot be said to think in the way that human beings or God can; these properties being made possible by mental substance. [[CiteRef::Des Chene (2001)]][[CiteRef::Clarke (1992)]][[CiteRef::Descartes (2007)]] Descartes posited a mental substance for theological, metaphysical, and scientific reasons. He supposed that thought could not be mechanized, since all the machines known to him were specialized to perform one particular function, but human reason was a general purpose instrument.[[CiteRef::Hatfield (1992)]][[CiteRef::Cottingham (1992)]]