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After leaving La Fleche, in 1618,Descartes became involved in a collaboration with the Dutch Calvinist natural philosopher Isaac Beeckman (1588-1687), who valued him for his mathematical skills. They worked together on several mathematical problems in natural philosophy. Beeckman was a corpuscularist. A derivative of atomism, '''corpuscularism''' rejected indivisible atoms and void spaces but nonetheless accounted for the properties of objects in terms of invisibly tiny particles [[CiteRef::Gaukroger (1995)|p. 68]] He is almost certainly the first person in Europe to attempt to explain macro-geometrical regularities in terms of micro-mechanical models. [[CiteRef::Gaukroger (1995)|p. 70]] For the most part, applying mathematics to physical problems was not part of the Aristotelian tradition. Descartes adopted Beeckman's mathematical corpuscularism and became part of a community of corpuscularist thinkers which besides Beeckman and Descartes included Marin Mersenne (1588-1648), Thomas Hobbes (1588-1679), Pierre Gassendi (1592-1655), Sir Kenelm Digby (1603-1665), and Walter Charleston (1620-1707). They all knew each other and reacted to each other's work.[[CiteRef::Osler (2001)]] The decade after Descartes met Beeckman was the most philosophically productive of his life. [[CiteRef::Garber (1992)]]
In terms of his methodology Descartes was largely responding to what he perceived as the dogmatism and marked lack of progress he saw in the Scholastic tradition, and his excitement with the new mechanical natural philosophy. His weariness with the largely dialectical scholastic method is what led him to develop the highly systematized epistemology and metaphysics for which he would come to be known. The Aristotelian-scholastic mosaic continued to be accepted throughout Descartes's life, with acceptance of his views coming later.
|Major Contributions=Descartes new methodology and mechanical natural philosophy were of revolutionary importance. They became accepted at Cambridge University in England by 1680,[[CiteRef::Barseghyan (2015)|p. 211]] and in France by about 1700, displacing the Aristotelian-medieval system of theories from the [[Scientific Mosaic|scientific mosaic]]. These theories were ultimately fully displaced throughout Europe by Descartes theories and by the later theories of Issac Newton (1642-1726).[[CiteRef::Barseghyan (2015)|p. 167]]
Descartes concluded that if his goal was to attain certain knowledge about the world,the accepted methodology must be rejected and a new one would be required. Methodology held a central place in his epistemology; in fact, one of Descartes’ criticisms of Galileo was that he failed to produce a fully developed methodology to justify his discoveries, and had simply explained particular physical phenomena.[[CiteRef::Ariew (1986)]] To that end he embraced his skeptical doubts and devised a methodology based on '''methodological skepticism'''; a methodology whereby he rejects all knowledge that he cannot be certain of, accepts only those propositions which he can accept as certain, and proceed deductively from those axioms according to reason. By this method Descartes hoped to produce a kind of systematized knowledge that, he believed, could be universally acceptable. In his 'Meditations on First Philosophy', [[CiteRef::Descartes (2004)]] Descartes identified the sole indubitable proposition upon which he would build the entire rest of his philosophical system as his famous '''‘Cogito, Ergo Sum’''' (also styled ‘Dubito, Ergo Cogito, Ergo Sum’ or simply as ‘the Cogito’); “I think, therefore I am.” From this foundation Descartes deduced that he was a created thing, his requiring a creator, that creator being God, the benevolent nature of God, and the consequent reliability of his God-given senses and reason, all of which formed the broader foundation of his systematized scientific worldview.[[CiteRef::Newman (2014)]]
Although Descartes maintained some methodological aspects of the Scholastic-Aristotelian mosaic – namely the axiomatic-deductive, epistemic-foundationalist structure of investigation – one critical difference in Descartes’ his methodology was the shift in the method of theory choice. It jettisons jettisoned the Aristotelian expectation that a theory must be experientially based and intuitively obvious for it to be acceptable, and although his system, as it ended up, allowed for knowledge that was both experiential and intuited,[[CiteRef::Newman (2014)]] the ultimate justification for knowledge claims was human reason. In this way Descartes is was both a '''rationalist''' and an a priorist, in that his epistemology and metaphysics allows for the existence of synthetic a priori propositions.
===The Cartesian Revolution in Natural Philosophy===
Descartes deduced his scientific theories about the natural world from a metaphysical foundation, in turn deduced by the application of his rationalist methodology. He wrote that "the whole of philosophy is like a tree. The roots are metaphysics, the trunk is physics, and the branches emerging from the trunk are all the other sciences, which may be reduced to three principle ones, namely medicine, mechanics, and morals".[[CiteRef::Clarke (1992)|p. 271]] One ought to construct a metaphysics first, based on criteria independent of observation, and subsequently consider physical theories consistent with the metaphysical foundation. His natural philosophy was in stark contrast to the accepted Aristotelianism, which emphasizes experience and intuition as routes to knowledge, rather than reason. In Aristotelian natural philosophy all objects were a compound of form and matter, a concept called hylomorphism. Form gives material bodies their distinctive properties, and makes them different from one another. It explains why fire rises and stones fall. Matter is what all material bodies share in common. All things have teleological goals or purposes [[CiteRef::Shields (2016)]].
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. Our senses, Descartes maintained, do not inform us of the mechanical world as it is, but provide us with sensations which are mere signs of their objective causes. 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'' were 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)]] 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)]] Aristotle's theory of physiology posited three souls or vital principles, the nutritive soul, responsible for nutrition and reproduction, and comprising 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 (2011)]][[CiteRef::Van der Eijk (2000)]] Descartes rejected the nutritive and sensitive souls, supposing their functions were instead performed by corpuscular mechanisms, which he outlined in his ''Treatise on Man''. [[CiteRef::Descartes (2007)]] Descartes mental substance served roughly the same role as Aristotles' intellectual soul. 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::DesChene (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)]]
Part about experimental method goes here p. 181 Barseghyan
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 his new views were threatening to the Catholic and 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 schoolsin the Catholic world.
In the early modern period, theological propositions and natural philosophical propositions both formed part of the same scientific mosaic, and thus [[The Zeroth Law|one needed reconciliation to be reconciled with the other]]. [[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''. This doctrine had been 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, while 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. The Anglican Christians church, the state church of England following its break with the Catholic papacy in the 1530's did not accept the ''doctrine of transubstantiation'' and thus . Thus Cartesianism did not face objections based on it, and became accepted at Cambridge University by 1680. Catholic Paris didn't accept it until 1700. Many solutions reconciling Cartesianism and the ''Real Presence'' were, by then, 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, and outside the ordinary course of nature described by Cartesianism.[[CiteRef::Barseghyan (2015)|p. 194]]
Another sort of objection raised in commentaries on Descartes had to do with the fact that corpuscular explanation involved hypothetical unobservable entities, and the supposition that this invisibly small world could be understood by analogy with larger objects. Descartes countered that "there is nothing more in keeping with reason that we judge about those things that we do not perceive, because of their small size, by comparison and contrast with those that we see" [[CiteRef::Clarke (1992)|p. 267]] He felt that a plausible model, though potentially incorrect due to the unobservability of its fundamental parts, was better than none at all. The role of unobservable entities and metaphysics in the physical sciences was to remain a matter of prolonged debate. The positing of unobservably small entities in explanations of observable phenomena has become an accepted and central practice of modern physics, and in other also modern fields such as biology which places a strong emphasis on the molecular biologybasis of biological phenomena.
One particularly notable objection came from Princess Elizabeth of Bohemia (1618-1680), 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 to this central question over the course of the correspondence. In 1747, in his ''L'Homme machine''(''Machine Man'') Julien Offray de La Mettrie (1709-1751) raised another simple, but devastating objection to Descartes' supposition that human reason must be due to an immaterial mental substance. He noted that reason can become impaired by material causes such as drunkenness and fever. [[CiteRef::La Mettrie (1996)]]. In the nineteenth century, Princess Elizabeth's objection became far more poignant with the formulation of the law of the conservation of energy which implied causal closure of the physical world to influence by a mental substance. In the early twentieth century, the mathematician Alan Turing (1912-1954) showed that it was possible to construct a general purpose machine capable of performing any possible mathematical computation, thereby demonstrating that a general purpose machine was possible and refuting Descartes' core argument against a mechanical understanding of human reason. By the end of the twentieth century, the relevant scientific communities of neuroscience and cognitive science had rejected the idea of a mental substance and sought a mechanistic physical explanation for the mind [[CiteRef::Bechtel (2008)]], though there was still no agreement as to whether consciousness could be explained in this fashion. [[CiteRef::Chalmers (1996)]]