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===The Cartesian Revolution in Natural Philosophy===

Descartes played a pivotal role in the transition away from the Scholastic-Aristotelian mosaic, and his physical, physiological, psychological, and biological theories are too numerous to be adequately treated here.[[CiteRef::Hatfield (2016)]][[CiteRef::Garber (1992)]] That said, a number of his theories are worth exploring in brief, in particular those that were fundamental departures from the accepted mosaic of the early sixteenth century. The first and most dramatic of these is Descartes’ rejection of hylomorphism and the form-matter distinction which would be the foundation for Descartes’ rejection of most of the prior physics. In place of the hylomorphic theory of substance Descartes proposed that there are in fact two kinds of substances that are entirely different from each other in composition and kind: mental substance and physical substance. Descartes equated the former with the rational soul of God and humans and the latter with all physical matter, the fundamental feature of which he considered to be extension. Descartes deduced his scientific theories about the natural world from this basically metaphysical foundation (all of which he deduces by application of his method). For example the central concept in Cartesian mechanics is that all material interactions are interactions between matter, which fills the universe (plenism also followed from Descartes’ position of matter as extension because if all matter is extended then there can be no space without extended matter, i.e. a vacuum). Descartes also considered the universe to be essentially mechanical in character except for mental substance – animals according to Descartes, as being constituted solely of material substance and without mental substance, are mere automata and cannot be said to think, feel, or love in the way that human beings or God can.[[CiteRef::Descartes (2007)]]