René Descartes

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René Descartes (31 March 1596 – 10 February 1650) was a French natural philosopher; who is today considered one of the most influential figures in modern philosophy. Descartes rejected the Aristotelian-medieval mosaic accepted for most of the previous two thousand years, and laid the foundations of a new mechanistic mosaic.1p. 52423 Aristotelians had maintained that intuition schooled by experience was the route to knowledge. Descartes, in his Discourse on the Method of Rightly Conducting One’s Reason and of Seeking Truth in the Sciences (Discourse on Method), first published in 1637,4 put forward a rationalist scientific methodology in which a proposition is acceptable only if it can be clearly and distinctly perceived by the intellect beyond all reasonable doubt or follows deductively from such propositions.2 This allowed him to advance a mathematical a priorist approach to scientific knowledge and inquiry.56 Rejecting the Aristotelian world of forms, substances, and teleology, he posited a mechanical world in which matter possessed only spatial extension and interacted only by contact. In mathematics he developed techniques that made possible analytic geometry. In natural philosophy, he was co-framer of the sine law of light refraction, developed a theory of the rainbow, and formulated a precursor of the nebular hypothesis of the origin of the solar system.7

Historical Context

The scientific mosaic of the late sixteenth and early seventeenth centuries was based primarily on the works of Aristotle and some later Hellenistic natural philosophers. This was reconciled in various ways with Christian theology by scholars in the High Middle Ages. This Aristotelian-scholastic mosaic included Ptolemaic astronomy, astrology, humoral physiology, and Christian (Catholic, in many but not all communities contemporaneous with Descartes) theology.8 Descartes was well educated in this tradition through his attendance at the prestigious Jesuit La Fleche College between the ages of ten and eighteen. He studied a traditional scholastic curriculum of logic, grammar, philosophy, mathematics, and theology. Natural philosophy was taught from the works of Aristotle as interpreted by Christian scholars. Descartes also received an education in mathematics that was unusual for the Aristotelian tradition, and excelled at math. 9pp. 38-61105

Descartes’ major writings came in a time of social and intellectual upheaval in Europe. Before writing his major works, he was a participant in the Thirty Years War. He travelled extensively around Europe at a time when the continent was embroiled in both reformation and counter-reformation, which were both a wellspring of new thought in theology and philosophy. The community of the time was engaged with major challenges to the Aristotelian-scholastic tradition. These came from varied sources, including varieties of Platonism, Hermeticism, and the chemical philosophy of Paracelsus, among other movements.5 There were new developments in optics, astronomy, and physiology.11 Aristotle's earth-centered cosmology had been challenged by the work of Nicolaus Copernicus(1473-1543), Johannes Kepler(1571-1630), and Galileo Galilei(1564-1642), which Descartes was familiar with.71012

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. 9p. 68 Beeckman was a supporter of the mechanical natural philosophy. This was a pursued radical alternative to Aristotelian cosmology, embraced by some supporters of Copernican heliocentrism.13149p. 69-73 It rejected the Aristotelian fundamentals of form, substance, and teleology, and the idea that matter is continuous. Instead of explaining the properties of visible bodies in terms of form, it maintained that the world consisted of invisibly tiny particles of matter and that all the observable properties of visible bodies were a consequence of these particles and their interactions. The particles were held to interact mechanically, by contact, and it was often supposed that this rendered natural phenomena potentially explainable in geometrical and mathematical terms. It can be traced to the Ancient Greek atomism of Democritus (circa 460-370 BCE) and later Epicurean philosophers. Atomism was reintroduced into European thought in the fifteenth century with the rediscovery of the Roman poet Lucretius's De rerum natura. Part of its appeal lay in the fact that unlike Aristotle's physics, the mechanical philosophy was compatible with a moving planetary Earth. In the early seventeenth century, it was championed by Giordano Bruno (1548-1600), Nicolas Hill (1570-1610?), Sebastian Basso (1573-1625?), Francis Bacon (1561-1626), and Galileo Galilei.5151613

Descartes and Beeckman worked together on several mathematical problems in natural philosophy. Beeckman is almost certainly the first person in Europe to attempt to explain macro-geometrical regularities in terms of micro-mechanical models. 9p. 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.17 The decade after Descartes met Beeckman was the most philosophically productive of his life. 5

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

Hakob Barseghyan's lecture on Cartesian Worldview

Descartes new methodology and mechanical natural philosophy were of revolutionary importance. They became accepted at Cambridge University in England by 1680,18p. 211 and in France by about 1700, displacing the Aristotelian-medieval system of theories that had been central elements of the scientific mosaic for centuries. These theories were ultimately fully displaced throughout Europe by Descartes' theories and by the later theories of Isaac Newton (1642-1726).18p. 167

Cartesian Methodology

Under the Aristotelian scholastic methodology a theory is acceptable “if it grasps the nature of a thing through intuition schooled by experience, or if it is deduced from general intuitive principles”.18p. 144 Descartes became frustrated with this tradition and its dialectical approach to knowledge-seeking, which he charged with plunging him into skeptical doubts whereby he could never be sure what was true and what was not. He writes in Discourse on Method:4

“But no sooner had I completed the whole course of study that normally takes one straight into the ranks of the ‘learned’ than I completely changed my mind about what this education could do for me. For I found myself tangled in so many doubts and errors that I came to think that my attempts to become educated had done me no good except to give me a steadily widening view of my ignorance!”

Descartes concluded that if his goal was to attain certain knowledge about the world,the accepted methodology for doing so must be rejected, and a new one formulated. 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.12 Rather than experience and intuition, Descartes' methodological skepticism was based on reason and on the capacity to doubt. The harder a proposition was to doubt, the greater its certainty. This was an epistemological innovation.

His strategy was, first, to reject all knowledge that he cannot be certain of, and accept only those propositions of which he is certain. He would deduce other knowledge from such axioms using reason. By this method Descartes hoped to produce a kind of systematized knowledge that could be universally accepted. In his Meditations on First Philosophy, 19 Descartes identified the sole indubitable proposition upon which he would build his entire philosophical system: he was certain of his own existence as a thinking being, or in Latin, ‘Cogito, Ergo Sum’ (also styled ‘Dubito, Ergo Cogito, Ergo Sum’ or simply as ‘the Cogito’); “I think, therefore I am.” From the foundation of his own existence, Descartes deduced that he must be a created being, that this requires a creator, that creator being God, the benevolent nature of God, and the consequent reliability of his senses and of the God-given ability of his reason to form clear and distinct ideas. It was therefore possible to use his senses and reason to gain knowledge of an external world. This reasoning formed the foundation of his systematized scientific worldview.2

Descartes maintained some aspects of the Scholastic-Aristotelian methodology – namely an axiomatic-deductive, epistemic-foundationalist structure of investigation. But the critical difference in his methodology was the shift in the method of theory choice. He 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,2 the ultimate justification for knowledge claims was human reason and the absence of doubt. Descartes was both a rationalist and an a priorist, in that his epistemology and metaphysics allows for the existence of synthetic a priori propositions. Although an argument for God's existence was at the foundation of his system, Descartes' rationalism was nonetheless a formidable challenge to the accepted theological methodology which had been comprehensively expressed by the Catholic saint, Thomas Aquinas (1225-1274) more than three hundred years earlier. Aquinas saw human reason as limited, and always to be exercised in the context of, and subject to the authority of, the divine revelation of the Bible. Descartes, by contrast, sought to develop his epistemology and theology on the basis of human reason alone. 20

Cartesian Natural Philosophy

Descartes scientific theories about the natural world were grounded in 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".6p. 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. 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. 21

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. 22 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 its Aristotelian form, determines its properties. Since corpuscles are too small to be directly observed, their size and shape must be hypothesized, 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. 6 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. 523

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. 5

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. 2425 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. 4 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. 2664 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.2711

Descartes mechanical natural philosophy fostered a radical change in how natural philosophers gained new knowledge. The Aristotelian-medieval methodology accorded a very limited role for experiments in scientific investigation. This is because a strict distinction was made between natural and artificial things. Every natural thing behaved in accordance with its nature; acorns grow on oak trees, because that is what their nature dictates. Artificial things have an external source of change. The cogs and springs of a clock are constructed so that they no longer behave according to their respective natures (which is simply to fall towards their natural place at the center of the universe, rather than function as parts of a machine that tells time for humans). A thing cannot reveal its true nature under the artificial conditions of experimentation, because the experimental set up necessarily puts things under artificial conditions. To gain knowledge, things must be observed in their natural undisturbed state. Descartes' mechanical natural philosophy rejected the natural/artificial distinction along with its rejection of forms and teleology. Matter always obeyed the same set of mechanical laws regardless of its situation. Thus,under the mechanical natural philosophy experimentation was often a good source of knowledge about nature, and its adherents often became practitioners. 18p.181-182

The challenge to 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 (that being is a compound of matter and form), 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, but had never before faced complete overhaul that Descartes's mechanical natural philosophy threatened. Although Descartes' theories would eventually be supplanted by those of Newton, he made the critical first steps to replacing the Aristotelian-scholastic mosaic.7


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.28 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 Catholic world. In the early modern period, theological propositions and natural philosophical propositions were not seen as belonging to separate domains, but rather formed parts of an integrated scientific mosaic. Aristotelian natural philosophy had been carefully adapted to render it consistent with Catholic faith. Descartes' novel natural philosophy introduced many inconsistencies that needed to be reconciled before his theories could be accepted. 18p. 190-196

One specific theological criticism of Cartesian natural philosophy had to do with the Catholic sacrament of the holy Eucharist, in which bread and wine are said to be transformed into the body and blood of Christ. The dogma of the Real Presence maintained that in this sacrament, Christ is really (as opposed to metaphorically or symbolically) present in the bread and wine. Thomas Aquinas had posited an Aristotelian explanation for the Real Presence which had become the accepted Catholic doctrine of transubstantiation. The doctrine held that in the Eucharist, the Aristotelian substance of the bread and wine were replaced by 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 church, the state church of England following its break with the Catholic papacy in the 1530's did not accept the doctrine of transubstantiation. 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 had, by then, been proposed. Barseghyan speculates that the one accepted by the Parisian community was that proposed by Antoine Arnauld (1612-1694) 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.18p. 194

Critics in Decartes' era were also concerned 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" 6p. 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 unobservably small entities in the physical sciences was to remain a matter of prolonged debate. In modern science, it is an accepted and central practice.

Another 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?”29 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. 30. 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 31, though there was still no agreement as to whether consciousness could be explained in this fashion. 32

Descartes' physical natural philosophy did not fare nearly so well. Within fifty years, Isaac Newton (1642-1726) formulated a more mathematically precise and explanatorily powerful physical theory, which became the accepted theory of the physical world. It rejected a major tenet of Descartes' corpuscularism by positing a gravitational force that acted at a distance. Newton's laws of motion, however, bore important similarities to those formulated earlier by Descartes. 6 As practicing scientists, researchers like Newton and Robert Boyle (1627-1691) did not, as did Descartes, seek certain knowledge of the real essences of material objects. Instead, they sought an ordering of phenomenal experience which would enable them to predict nature's course with the best available theory. 33

Descartes' method itself was criticized by two sympathetic figures; Antoine Arnauld and Marin Mersenne. Their criticism had to do with Descartes demonstration of the existence of God, which is the linchpin of his method. Descartes claimed that our belief in the reliability of the clear and distinct perceptions of the human intellect depends on our knowledge of the existence of God as the source of that capacity. But how could that knowledge be established in the first place? If we answer that we can prove God's existence from premises we clearly and distinctly perceive, then the argument collapses into circularity. Descartes' argument that it is possible for us to have certain scientific knowledge of the world fails with it, since it depends on God to underwrite the reliability of our senses and intellect. This criticism, called the Cartesian Circle, was never successfully countered. Within a generation, Descartes quest for certainty in scientific knowledge was widely recognized to have failed. 11 In 1650, John Locke and the British Empiricists brought forth a new conception of scientific knowledge that was more modest than Descartes' failed quest for certainty. The empiricists argued for experience, rather than a priori reason, as the basis for human knowledge, and sought a philosophy of science more in keeping with scientific practice. 3433


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Related Topics



  1. ^  Russell, Bertrand. (1945) A History of Western Philosophy. Routledge.
  2. a b c d  Newman, Lex. (2014) Descartes' Epistemology. In Zalta (Ed.) (2016). Retrieved from
  3. ^  Garber, Daniel. (1993) Descartes and Experiment in the Discourse and Essays. In Voss (Ed.) (1993), 288-310.
  4. a b c d  Descartes, René. (2007) Discourse on the Method. Early Modern Texts. Retrieved from
  5. a b c d e f g  Garber, Daniel. (1992) Descartes' Physics. In Cottingham (Ed.) (1992), 286-334.
  6. a b c d e f  Clarke, Desmond. (1992) Descartes' Philosophy of Science and the Scientific Revolution. In Cottingham (Ed.) (1992), 258-285.
  7. a b c  Hatfield, Gary. (2016) Rene Descartes. In Zalta (Ed.) (2016). Retrieved from
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  9. a b c d  Gaukroger, Stephen. (1995) Descartes: An Intellectual Biography. Clarendon Press, Oxford.
  10. a b  Rodis-Lewis, Genevieve. (1992) Descartes' Life and the Development of His Philosophy. In Cottingham (Ed.) (1992), 21-57.
  11. a b c  Cottingham, John. (1992) Introduction. In Cottingham (Ed.) (1992), 1-20.
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  13. a b  Luthy, Chirstopher; Murdoch, John E. and Newman, William R. (2001) Introduction: Corpuscles, Atoms, Particles, and Minima. In Luthy, Murdoch, and Newman (Eds.) (2001), 1-38.
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  18. a b c d e f  Barseghyan, Hakob. (2015) The Laws of Scientific Change. Springer.
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  23. ^  Descartes, René. (2003) Treatise on Man. Prometheus Books.
  24. ^  Shields, Christopher. (2016) Aristotle's Psychology. In Zalta (Ed.) (2016). Retrieved from
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  26. ^  Des Chene, Dennis. (2001) Spirits and Clocks: Machine and Organism in Descartes. Cornell University Press.
  27. ^  Hatfield, Gary. (1992) Descartes' Physiology and its Relation to his Psychology. In Cottingham (Ed.) (1992), 335-370.
  28. ^  Jolley, Nicholas. (1992) The Reception of Descartes' Philosophy. In Cottingham (Ed.) (1992), 393-423.
  29. ^  Descartes, René. (2009) Correspondence with Princess Elizabeth. Early Modern Texts. Retrieved from
  30. ^  De La Mettrie, Julien Offray. (1996) Machine Man and Other Writings. Cambridge University Press.
  31. ^  Bechtel, William. (2008) Mental Mechanisms: Philosophical Perspectives on Cognitive Neuroscience. Lawrence Erlbaum Associates.
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  33. a b  Osler, Margaret. (1970) John Locke and the Changing Ideal of Scientific Knowledge. Journal of the History of Ideas 31 (1), 3-16.
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