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As Descartes said to his close correspondent, Marin Mersenne, “I may tell you, between ourselves, that these six Meditations contain all the foundations of my physics. But please do not tell people, for that might make it harder for supporters of Aristotle to approve of them. I hope that readers will gradually get used to my principles, and recognize their truth, before they notice that they destroy the principles of Aristotle” (18 January 1641). The Meditations attempts a complete intellectual revolution: the replacement of Aristotelian philosophy with a new philosophy in order to replace Aristotelian science with a new science. For a 17th-century Aristotelian, a body is matter informed by substantial and accidental forms, and change is explained by the gain or loss of such forms: in mutation by the acquisition of a substantial form, and in what Aristotelians would call true motion (that is, augmentation and diminution, alteration, or local motion) by the successive acquisition of places or of qualitative or quantitative forms. The mechanist program consisted in doing away with qualitative forms and reducing all changes to something mathematically quantifiable: matter in motion. As Descartes said in The World, not only the four qualities called heat, cold, moistness, and dryness, “but also all the others
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