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In Descartes' mechanical corpuscular natural philosophy, by contrast, there are just two kinds of substance that are entirely different from each other in kind: mental substance and physical substance. The fundamental property of '''mental substance''' was thought, and Descartes equated it with the rational soul of God and humans. The fundamental feature of '''physical substance''' was extension in space. He rejected Aristotle's distinction between form and matter, including Aristotle's four elements. [[CiteRef::Ariew (1992)]] Cartesian mechanics rejects the void posited by atomists; instead matter fills the universe as a plenum. If all matter is extended, Descartes reasoned that there can be no space without extended matter. Also unlike atomism, matter is infinitely divisible, though visible things are composed of tiny corpuscles that interact with one another by physical contact. The corpuscular composition of a material body, rather than form, determines its properties. Since corpuscles are too small to be directly observed, their size and shape is hypothetical, though observation can allow us to infer the plausibility of our guesswork.
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. Earth, as a moving planet, is the center of its own smaller vortex. 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)]] Animals, according to Descartes, are complex automata composed of physical substance only and cannot be said to think, feel, or love in the way that human beings or God can; these properties being made possible by mental substance [[CiteRef::Clarke (1992)]][[CiteRef::Descartes (2007)]]. All the machines known to Descartes were specialized to perform just one function, but human reason was a general purpose instrument. Thus, Descartes supposed, thought could not be mechanized. [[CiteRef::Hatfield (1992)]][[CiteRef::Cottingham (1992)]]
Descartes maintained that our senses do not inform us of the mechanical world as it is, but provide us with sensations which are mere signs of their objective cause. Only extended matter and motion exist apart from our minds. Secondary qualities, such as colors, are created in our minds in response to mechanical stimuli. [[CiteRef::Clarke (1992)]] Descartes completed a manuscript that was to be a comprehensive expression of his mechanical natural philosophy, called ''The World''. He withdrew his plans to publish it upon learning of the condemnation of Galileo in Rome in 1633. The work never appeared during his lifetime, but two major fragments, the ''Treatise on Light'', and the ''Treatise on Man'' where published posthumously. The first dealt with physics, and the second put forward a theory of physiology, nervous system function, and the mind/brain relationship. [[CiteRef::Garber (1992)]][[CiteRef::Descartes (2003)]]
The overthrow of the Aristotelian tradition, even in places where Cartesianism was rejected and the community maintained Aristotelianism, forced the academic community in Europe to reconsider and defend the Aristotelian mosaic in ways that had never before been encountered. Though the dialectical approach to scholarship throughout the medieval period saw scholars constantly questioning various aspects of the Aristotelian worldview, Descartes’ wholesale rejection of huge swaths of the mosaic and its central concepts were unprecedented. Theories like hylomorphism, which had been a given in the mosaic of the sixteenth and early seventeenth centuries and had endured through multitudes of adjustments, reconciliations and dialectic criticism had never before faced complete overhaul as Descartes threatened. Although Descartes theories would eventually be supplanted by those of Newton, he made the critical first steps to replacing the Aristotelian-scholastic mosaic.[[CiteRef::Hatfield (2016)]]
|Criticism=Descartes’ ideas saw widespread criticism in his time and shortly after from all manner of sources, including Scholastic vanguards, religious authorities, and other philosophers. One common early criticism was that Descartes' new views were threatening to the Christian faith. [[CiteRef::Jolley (1992)]] In 1663, his works were placed on the Catholic Church's ''Index of Forbidden books'', and in 1671 his conception was officially banned from schools. In the early modern period, theological propositions and natural philosophical propositions both formed part of the same scientific mosaic. [[CiteRef::Barseghyan (2015)|p. 190-196]] One specific theological criticism of Descartes was that his mechanistic corpuscular natural philosophy could not be easily reconciled with the Catholic ''doctrine of transubstantiation'' proposed by Thomas Aquinas as an Aristotelian explanation for the Christian dogma of the ''Real Presence''. The dogma maintained that in the sacrament of the Eucharist, Christ is really (as opposed to metaphorically or symbolically) present in the bread and wine. Aquinas had posited that the Aristotelian substance of the bread and wine were replaced with the body and blood of Christ, but their forms (that of bread and wine) remaining unchanged. In Descartes' corpuscularism, bread and wine differed from flesh and blood because they had a different arrangement of corpuscles. There is no obvious way that one could appear as the other. Anglican Christians did not accept the ''doctrine of transubstantiation'' and thus Cartesianism became accepted at Cambridge University by 1680. Catholic Paris didn't accept it until 1700. Many solutions reconciling Cartesianism and the ''Real Presence'' were proposed. Barseghyan speculates that the one accepted by the Parisian community was that proposed by Antoine Arnauld in 1671, in which Christ's presence in the Eucharist was due to a miracle beyond human comprehension.[[CiteRef::Barseghyan (2015)|p. 194]]
The most notable objection Descartes would end up facing would be the more mathematically precise and more explanatorily powerful physical theory given by Newton half a century later, but there existed objection to Descartes even earlier. One particularly notable objection came from Princess Elizabeth of Bohemia, who questioned Descartes’ theory of substance in a letter dated the tenth of May, 1643. In it, she asks “Given that the soul of a human being is only a thinking substance, how can it affect the bodily spirits, in order to bring about voluntary actions?”[[CiteRef::Descartes (2009)]] Descartes would never gives a satisfactory answer over the course of the correspondence, and the single example highlights how troubling the issues left open by Descartes’ system are for the integrity of that system. Elizabeth’s objection raises reasonable (significant, even) doubts about whether or not the theory of substance around which Descartes bases a significant portion of his scientific theories can hold water.
One of the most powerful objections to arise after Descartes’ death in 1650 came a generation later with the emergence of the philosophy of John Locke and the British Empiricists. Locke, despite being an admirer of Descartes, was highly critical of his methodology and in particular was critical of his methodological scepticismskepticism, which Locke regarded as a non-starter.[[CiteRef::Uzgalis (2016)]]
Other objections were political, theological, and personal objections brought by various interest groups who had some stake in the academic status quo. In many places Descartes’ work was banned, in more even discussion of Descartes’ work was banned. Official condemnations came down from Universities universities and Church authorities, none of which were effective at stopping the spread of Cartesian ideas.[[CiteRef::Jolley (1992)]]
|Related Topics=Method, Methodology,
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