Rene Descartes Mathematician Essays On Abortion

Ren� Descartes (1596 - 1650) was a French philosopher, mathematician, scientist and writer of the Age of Reason. He has been called the "Father of Modern Philosophy", and much of subsequent Western philosophy can be seen as a response to his writings. He is responsible for one of the best-known quotations in philosophy: "Cogito, ergo sum" ("I think, therefore I am").

He was a pioneer and major figure in 17th Century Continental Rationalism (often known as Cartesianism) later advocated by Baruch Spinoza and Gottfried Leibniz, and opposed by the British Empiricist school of thought of Hobbes, Locke, Berkeley and Hume. He represents a major break with the Aristotelianism and Scholasticism of the Medieval period.

His contribution to mathematics was also of the first order, as the inventor of the Cartesian coordinate system and the founder of analytic geometry, crucial to the invention of calculus and mathematical analysis. He was also one of the key figures in the scientific revolution of the 16th and 17th Centuries.

Descartes (pronounced day-CART) was born in the town of La Haye en Touraine (since renamed Descartes) in the Loire Valley in central France on 31 March 1596. His father, Joachim Descartes, was a busy lawyer and magistrate in the High Court of Justice, and his mother, Jeanne (n�e Brochard), died of tuberculosis when Ren� was just one year old. Ren� and his brother and sister, Pierre and Jeanne, were therefore mainly raised by their grandmother.

From 1604 until 1612, he attended the Jesuit Coll�ge Royal Henry-Le-Grand at La Fl�che, Anjou, studying classics, logic and traditional Aristotelianism philosophy. His health was poor and he was granted permission to remain in bed until 11 o'clock in the morning, a custom he maintained for the rest of his life. He then spent some time in Paris studying mathematics, before studing law at the University of Poitiers, in accordance with his father's wishes that he should become a lawyer, obtaining his law degree in 1616.

However, he then abandoned his education and spent several years travelling and experiencing the world (he later claimed that his formal education provided little of substance). It was during this time (in 1618) that he met the Dutch philosopher and scientist Isaac Beeckman (1588 - 1637) while walking through Breda in Holland, who sparked his interest in mathematics and the new physics.

In 1622, he returned to France, and soon afterwards sold all his property at La Haye, investing the proceeds in bonds which provided him with a comfortable income for the rest of his life. He returned to settle in Holland in 1628. The next year, he joined the University of Franeker; the year after that, Leiden University; and, in 1635, he is recorded as attending Utrecht University. He had a daughter, Francine, after a relationship in Amsterdam with a servant girl, Hel�ne Jans, although Francine died at the age of fve. In fact, in the years between 1828 and 1649, he lived at 14 separate addresses in 10 different Dutch cities.

It was during this 20 year period of frequent moves that he wrote almost all of his major works on philosophy, mathematics and science. He shrewdly held off publication of his first work, "Le Monde" ("The World"), written between 1629 and 1633, due to the condemnation of the works of Galileo Galilei (1564 - 1642) and Nicolaus Copernicus (1473 - 1543) by the Roman Catholic Church in 1633. The most famous of his works include: the "Discours de la m�thode pour bien conduire sa Raison et chercher la V�rit� dans les Sciences" ("Discourse on the Method") of 1637, his first rationalist vision of the progress of human knowledge; the "Meditationes de Prima Philosophia" ("Meditations on First Philosophy") of 1641, a more formal exposition of his central tenets, in Latin; and the "Principia Philosophiae" ("Principles of Philosophy") of 1644, an even more systematic and comprehensive exposition of his views. For a time, in 1643, Cartesian philosophy was condemned by the University of Utrecht.

Descartes died of pneumonia on 11 February 1650 in Stockholm, Sweden, where he had been invited as a teacher for Queen Christina of Sweden. Later, his remains were taken to France and buried in the church of Sainte-Genevi�ve-du-Mont in Paris, and then, during the French Revolution, disinterred for burial in the Panth�on among the other great thinkers of France. Currently, his tomb is in the church of Saint-Germain-des-Pr�s in Paris, and his brain is in the Mus�e de l'Homme.

Descartes lived during a very skeptical period, at a time before science as we know it existed, and after a long period of relative stagnation in philosophical thought during the Church-dominated and Aristotle-influenced late Middle Ages. He had been impressed, in both his academic work and in his experience of the world at large, by the realization that there appeared to be no certain way of acquiring knowledge, and he saw his main task as the epistemological one of establishing what might be certain knowledge as a stepping stone towards the ultimate pursuit of truth. His more immediate aim in this was to put scientific enquiry in a position where it was no longer subject to attack by Skeptics, and he tried to do this by a kind of pre-emptiveSkepticism, essentially by being more skeptical than the Skeptics.

At the heart of Descartes' philosophical method was his refusal to accept the authority of previous philosophers, and even of the evidence of his own senses, and to trust only that which was clearly and distinctly seen to be beyond any doubt (a process often referred to as methodological skepticism or Cartesian doubt or hyperbolic doubt). Only then did he allow himself to reconstruct knowledge (piece by piece, such that at no stage was the possibility of doubt allowed to creep back in) in order to acquire a firm foundation for genuine knowledge and to dispel any Skepticism.

He outlined four main rules for himself in his thinking:

  • Never accept anything except clear and distinct ideas.
  • Divide each problem into as many parts are needed to solve it.
  • Order your thoughts from the simple to the complex.
  • Always check thoroughly for oversights.

Using this process, which he detailed in his epochal "Discourse on the Method" of 1637 and expanded in the "Meditations on First Philosophy" of 1641, Descartes attempted to narrow down, by what is sometimes called the method of doubt, what was certain and what contained even a shadow of a doubt. For example, he realized that he could doubt even something as apparently fundamental as whether he had a body (it could be that he was just dreaming of it or that it was an illusion created by an evil demon), but he could not, under any circumstances, doubt whether he had a mind or that he could think. He followed this up with a pure, abstract thought experiment. He imagined an evil spirit (or "deceiving demon") whose sole intention was to mislead him, and asked whether there was anything about which the demon would not be able to mislead him. His conclusion was the act of thinking, that the demon could never make him believe that he was thinking when he was not (because, after all, even a false thought is still a thought).

Having identified this single indubitable principle, that thought exists, he then argued that, if someone was wondering whether or not he existed, then the very act of thinking was, in and of itself, proof that he did in fact exist: the famous "Je pense, donc je suis" ("I think, therefore I am") - the similar statement in Latin, "Cogito ergo sum" is found in his later "Principles of Philosophy". It is worth mentioning here that, by "thinking", Descartes did not just mean conceptual thought, but all forms of consciousness, experience, feelings, etc.

Having dispelled all doubt by this process, Descartes then worked to build up, or reconstitute, the world again. But he was careful not to do this willy-nilly, but only according to his own very strict rules, so that the "reconstituted world" was not the same as the original one which he had dismantled piece by piece due to doubts. The way he achieved this (which, it must be said, appears from a modern viewpoint like something of a conjuring trick) was to argue that among the contents of our (certain) consciousness was the idea of God, which in itself he saw as proof of the existence of God. He then argued that, if we have the overwhelming impression of the existence of a concrete world around us, as we do, then an omnipotent, omniscient and omnibenevolent God would ensure that such a world does in fact exist for us. Furthermore, he asserted that the essence of this physical world was extension (that it takes up space), contrary to the extensionless world of the mind.

Paradoxically, this was an essential step forward in 17th Century science as it established a physical world which was of a mathematical character and permitted mathematical physics to be used to explain it. Also important is that, as we have seen, although God was indispensible to Descartes' method of arriving at a physical world, once such a world was accepted, it was no longer necessary to involve God in the description and measurement and explanation of how things work. Thus, the process of science was freed from theological contraints and interference.

Descartes dismissed the senses and perception as unreliable, and to demonstrate this he used the so-called Wax Argument. This revolves around the idea that a wax object, which has certain properties of size, colour, smell, temperature, etc, appears to change almost all of these properties when it is melted, to the extent that it appears to our senses to be a completely different thing. However, we know that it is in fact still the same piece of wax. Descartes concluded from this that the senses can be misleading and that reason and deduction is the only reliable method of attaining knowledge, which is the essence of Rationalism.

Descartes further argued that sensory perceptions come to him involuntarily (not willed by him), and are therefore external to his senses and therefore evidence of the existence of an external world outside of his mind. He argued that the things in the external world are material because God would not deceive him as to the ideas that are being transmitted, and has given him the propensity to believe that such ideas are caused by material things. Because of this belief that God is benevolent and does not desire to deceive him, he can therefore have some faith in the account of reality his senses provide him.

Descartes believed that the human body works like a machine, that it has the material properties of extension and motion, and that it follows the laws of physics. The pieces of the human machine, he argued, are like clockwork mechanisms, and that the machine could be understood by taking its pieces apart, studying them, and then putting them back together to see the larger picture (an idea referred to as Reductionism). The mind or soul, on the other hand, is a non-material entity that lacks extension and motion, and does not follow the laws of physics.

Descartes was the first to formulate the mind-body problem in the form in which it exists today (see the section on Philosophy of Mind), and the first to clearly identify the mind with consciousness and self-awareness, and to distinguish this from the brain, which was the physical seat of intelligence (Dualism). In his epistemological work in the "Discourse on the Method", he had realized that, although he could doubt that he possessed a body, he could not under any circumstances doubt that he possessed a mind, which led him to conclude that the mind and the body were two very different and separate things. His particular form of Dualism (known as Cartesian Dualism) proposed that the mind controls the body, but that the body also influences the otherwise rational mind (such as when people act out of passion) in a kind of two-way interaction, which he claimed, without much evidence, occurred in the pineal gland. Gilbert Ryle later described this kind of Dualism (where mental activity carries on in parallel to physical action, but where their means of interaction are unknown or, at best, speculative) as the "ghost in the machine". Although his own solution was far from convincing, this kind of Cartesian Dualism set the agenda for philosophical discussion of the mind-body problem for many years after Descartes' death.

It should be noted, however, that for all Descartes' innovation and boldness, he does not abandon the traditional idea of God. He defined "substance" (essentially meaning what the world really consists of) as "that which requires nothing other than itself in order to exist", but he concluded that the only true substance was God himself, because everything else (from souls to material objects like the human body) was dependent on God for its existence. He used his own variations of the causal argument, the ontological argument and the cosmological argument for the existence of God in his "Meditations" (see the section on Philosophy of Religion), and the existence of God played a major role in his validation of reason and in other parts of Descartes� system. Given the important r�le God plays in his work, suggestions that Descartes was really a closet atheist, and that he includes the arguments for the existence of God as window dressing, appear extremely unlikley.

In mathematics, Descartes realized that a graph could be drawn to show a geometrical interpretation of a mathematical function using points known as Cartesian coordinates, and thereby founded analytic geometry or Cartesian geometry (using algebra to describe geometry), which was crucial to the subsequent development of calculus by Sir Isaac Newton (1643 - 1727) and Gottfried Leibniz. He also invented the notation which uses superscripts to indicate powers or exponents, and his rule of signs is also a commonly used method to determine the number of positive and negative zeros of a polynomial. It can be argued that his reflections on mind and mechanism, impelled by the invention of the electronic computer and by the possibility of machine intelligence, blossomed into the Turing test of a machine's capability to demonstrate intelligence.

In optics, he showed by using geometric construction and the law of refraction (also known as Descartes' law) that the angular radius of a rainbow is 42 degrees. He also independently discovered the law of reflection (that the angle of incidence equals the angle of reflection).

In physics, Descartes introduced (before Newton) the concept of momentum of a moving body (what he termed the "amount of motion"), which he defined as the product of the mass of the body and its velocity or speed. His three "laws of nature" became the basis of Newton's later laws of motion and the modern theory of dynamics: that each thing tries to remain in the same state and, once moved, continues to move; that all movement is along straight lines; and that when a body comes into contact with another body the combined "quantity of motion" remain the same (his conservation of motion principle).

In an attempt to explain the orbits of planets, Descartes also constructed his vortex theory which would become the most popular theory of planetary motion of the late 17th Century (although subsequently discredited). However, he continued to cling to the traditional mechanical philosophy of the 17th Century, which held that everything physical in the universe to be made of tiny "corpuscles" of matter (although, unlike Atomism, the theory maintained that there could be no vacuum, just a mass of swirling matter).

René Descartes, (born March 31, 1596, La Haye, Touraine, France—died February 11, 1650, Stockholm, Sweden), French mathematician, scientist, and philosopher. Because he was one of the first to abandon scholastic Aristotelianism, because he formulated the first modern version of mind-body dualism, from which stems the mind-body problem, and because he promoted the development of a new science grounded in observation and experiment, he has been called the father of modern philosophy. Applying an original system of methodical doubt, he dismissed apparent knowledge derived from authority, the senses, and reason and erected new epistemic foundations on the basis of the intuition that, when he is thinking, he exists; this he expressed in the dictum “I think, therefore I am” (best known in its Latin formulation, “Cogito, ergo sum,” though originally written in French, “Je pense, donc je suis”). He developed a metaphysicaldualism that distinguishes radically between mind, the essence of which is thinking, and matter, the essence of which is extension in three dimensions. Descartes’s metaphysics is rationalist, based on the postulation of innate ideas of mind, matter, and God, but his physics and physiology, based on sensory experience, are mechanistic and empiricist.

Early life and education

Although Descartes’s birthplace, La Haye (now Descartes), France, is in Touraine, his family connections lie south, across the Creuse River in Poitou, where his father, Joachim, owned farms and houses in Châtellerault and Poitiers. Because Joachim was a councillor in the Parlement of Brittany in Rennes, Descartes inherited a modest rank of nobility. Descartes’s mother died when he was one year old. His father remarried in Rennes, leaving him in La Haye to be raised first by his maternal grandmother and then by his great-uncle in Châtellerault. Although the Descartes family was Roman Catholic, the Poitou region was controlled by the Protestant Huguenots, and Châtellerault, a Protestant stronghold, was the site of negotiations over the Edict of Nantes (1598), which gave Protestants freedom of worship in France following the intermittentWars of Religion between Protestant and Catholic forces in France. Descartes returned to Poitou regularly until 1628.

In 1606 Descartes was sent to the Jesuit college at La Flèche, established in 1604 by Henry IV (reigned 1589–1610). At La Flèche, 1,200 young men were trained for careers in military engineering, the judiciary, and government administration. In addition to classical studies, science, mathematics, and metaphysics—Aristotle was taught from scholastic commentaries—they studied acting, music, poetry, dancing, riding, and fencing. In 1610 Descartes participated in an imposing ceremony in which the heart of Henry IV, whose assassination that year had destroyed the hope of religious tolerance in France and Germany, was placed in the cathedral at La Flèche.

In 1614 Descartes went to Poitiers, where he took a law degree in 1616. At this time, Huguenot Poitiers was in virtual revolt against the young King Louis XIII (reigned 1610–43). Descartes’s father probably expected him to enter Parlement, but the minimum age for doing so was 27, and Descartes was only 20. In 1618 he went to Breda in the Netherlands, where he spent 15 months as an informal student of mathematics and military architecture in the peacetime army of the Protestant stadholder, Prince Maurice (ruled 1585–1625). In Breda, Descartes was encouraged in his studies of science and mathematics by the physicist Isaac Beeckman (1588–1637), for whom he wrote the Compendium of Music (written 1618, published 1650), his first surviving work.

Descartes spent the period 1619 to 1628 traveling in northern and southern Europe, where, as he later explained, he studied “the book of the world.” While in Bohemia in 1619, he invented analytic geometry, a method of solving geometric problems algebraically and algebraic problems geometrically. He also devised a universal method of deductive reasoning, based on mathematics, that is applicable to all the sciences. This method, which he later formulated in Discourse on Method (1637) and Rules for the Direction of the Mind (written by 1628 but not published until 1701), consists of four rules: (1) accept nothing as true that is not self-evident, (2) divide problems into their simplest parts, (3) solve problems by proceeding from simple to complex, and (4) recheck the reasoning. These rules are a direct application of mathematical procedures. In addition, Descartes insisted that all key notions and the limits of each problem must be clearly defined.

Descartes also investigated reports of esoteric knowledge, such as the claims of the practitioners of theosophy to be able to command nature. Although disappointed with the followers of the Catalan mystic Ramon Llull (1232/33–1315/16) and the German alchemist Heinrich Cornelius Agrippa von Nettesheim (1486–1535), he was impressed by the German mathematician Johann Faulhaber (1580–1635), a member of the mystical society of the Rosicrucians.

Descartes shared a number of Rosicrucian goals and habits. Like the Rosicrucians, he lived alone and in seclusion, changed his residence often (during his 22 years in the Netherlands, he lived in 18 different places), practiced medicine without charge, attempted to increase human longevity, and took an optimistic view of the capacity of science to improve the human condition. At the end of his life, he left a chest of personal papers (none of which has survived) with a Rosicrucian physician—his close friend Corneille van Hogelande, who handled his affairs in the Netherlands. Despite these affinities, Descartes rejected the Rosicrucians’ magical and mystical beliefs. For him, this period was a time of hope for a revolution in science. The English philosopher Francis Bacon (1561–1626), in Advancement of Learning (1605), had earlier proposed a new science of observation and experiment to replace the traditional Aristotelian science, as Descartes himself did later.

In 1622 Descartes moved to Paris. There he gambled, rode, fenced, and went to the court, concerts, and the theatre. Among his friends were the poets Jean-Louis Guez de Balzac (1597–1654), who dedicated his Le Socrate chrétien (1652; “Christian Socrates”) to Descartes, and Théophile de Viau (1590–1626), who was burned in effigy and imprisoned in 1623 for writing verses mocking religious themes. Descartes also befriended the mathematician Claude Mydorge (1585–1647) and Father Marin Mersenne (1588–1648), a man of universal learning who corresponded with hundreds of scholars, writers, mathematicians, and scientists and who became Descartes’s main contact with the larger intellectual world. During this time Descartes regularly hid from his friends to work, writing treatises, now lost, on fencing and metals. He acquired a considerable reputation long before he published anything.

At a talk in 1628, Descartes denied the alchemist Chandoux’s claim that probabilities are as good as certainties in science and demonstrated his own method for attaining certainty. The Cardinal Pierre de Bérulle (1575–1629)—who had founded the Oratorian teaching congregation in 1611 as a rival to the Jesuits—was present at the talk. Many commentators speculate that Bérulle urged Descartes to write a metaphysics based on the philosophy of St. Augustine as a replacement for Jesuit teaching. Be that as it may, within weeks Descartes left for the Netherlands, which was Protestant, and—taking great precautions to conceal his address—did not return to France for 16 years. Some scholars claim that Descartes adopted Bérulle as director of his conscience, but this is unlikely, given Descartes’s background and beliefs (he came from a Huguenot province, he was not a Catholic enthusiast, he had been accused of being a Rosicrucian, and he advocated religious tolerance and championed the use of reason).

Residence in the Netherlands

Descartes said that he went to the Netherlands to enjoy a greater liberty than was available anywhere else and to avoid the distractions of Paris and friends so that he could have the leisure and solitude to think. (He had inherited enough money and property to live independently.) The Netherlands was a haven of tolerance, where Descartes could be an original, independent thinker without fear of being burned at the stake—as was the Italian philosopher Lucilio Vanini (1585–1619) for proposing natural explanations of miracles—or being drafted into the armies then prosecuting the Catholic Counter-Reformation. In France, by contrast, religious intolerance was mounting. The Jews were expelled in 1615, and the last Protestant stronghold, La Rochelle, was crushed—with Bérulle’s participation—only weeks before Descartes’s departure. In 1624 the French Parlement passed a decree forbidding criticism of Aristotle on pain of death. Although Mersenne and the philosopher Pierre Gassendi (1592–1655) did publish attacks on Aristotle without suffering persecution (they were, after all, Catholic priests), those judged to be heretics continued to be burned, and laymen lacked church protection. In addition, Descartes may have felt jeopardized by his friendship with intellectual libertines such as Father Claude Picot (d. 1668), a bon vivant known as “the Atheist Priest,” with whom he entrusted his financial affairs in France.

In 1629 Descartes went to the university at Franeker, where he stayed with a Catholic family and wrote the first draft of his Meditations. He matriculated at the University of Leiden in 1630. In 1631 he visited Denmark with the physician and alchemist Étienne de Villebressieu, who invented siege engines, a portable bridge, and a two-wheeled stretcher. The physician Henri Regius (1598–1679), who taught Descartes’s views at the University of Utrecht in 1639, involved Descartes in a fierce controversy with the Calvinist theologian Gisbertus Voetius (1589–1676) that continued for the rest of Descartes’s life. In his Letter to Voetius of 1648, Descartes made a plea for religious tolerance and the rights of man. Claiming to write not only for Christians but also for Turks—meaning Muslims, libertines, infidels, deists, and atheists—he argued that, because Protestants and Catholics worship the same God, both can hope for heaven. When the controversy became intense, however, Descartes sought the protection of the French ambassador and of his friend Constantijn Huygens (1596–1687), secretary to the stadholder Prince Frederick Henry (ruled 1625–47).

In 1635 Descartes’s daughter Francine was born to Helena Jans and was baptized in the Reformed Church in Deventer. Although Francine is typically referred to by commentators as Descartes’s “illegitimate” daughter, her baptism is recorded in a register for legitimate births. Her death of scarlet fever at the age of five was the greatest sorrow of Descartes’s life. Referring to her death, Descartes said that he did not believe that one must refrain from tears to prove oneself a man.

The World and Discourse on Method

In 1633, just as he was about to publish The World (1664), Descartes learned that the Italian astronomer Galileo Galilei (1564–1642) had been condemned in Rome for publishing the view that the Earth revolves around the Sun. Because this Copernican position is central to his cosmology and physics, Descartes suppressed The World, hoping that eventually the church would retract its condemnation. Although Descartes feared the church, he also hoped that his physics would one day replace that of Aristotle in church doctrine and be taught in Catholic schools.

Descartes’s Discourse on Method (1637) is one of the first important modern philosophical works not written in Latin. Descartes said that he wrote in French so that all who had good sense, including women, could read his work and learn to think for themselves. He believed that everyone could tell true from false by the natural light of reason. In three essays accompanying the Discourse, he illustrated his method for utilizing reason in the search for truth in the sciences: in Dioptrics he derived the law of refraction, in Meteorology he explained the rainbow, and in Geometry he gave an exposition of his analytic geometry. He also perfected the system invented by François Viète for representing known numerical quantities with a, b, c, …, unknowns with x, y, z, …, and squares, cubes, and other powers with numerical superscripts, as in x2, x3, …, which made algebraic calculations much easier than they had been before.

In the Discourse he also provided a provisional moral code (later presented as final) for use while seeking truth: (1) obey local customs and laws, (2) make decisions on the best evidence and then stick to them firmly as though they were certain, (3) change desires rather than the world, and (4) always seek truth. This code exhibits Descartes’s prudential conservatism, decisiveness, stoicism, and dedication. The Discourse and other works illustrate Descartes’s conception of knowledge as being like a tree in its interconnectedness and in the grounding provided to higher forms of knowledge by lower or more fundamental ones. Thus, for Descartes, metaphysics corresponds to the roots of the tree, physics to the trunk, and medicine, mechanics, and morals to the branches.


In 1641 Descartes published the Meditations on First Philosophy, in Which Is Proved the Existence of God and the Immortality of the Soul. Written in Latin and dedicated to the Jesuit professors at the Sorbonne in Paris, the work includes critical responses by several eminent thinkers—collected by Mersenne from the Jansenist philosopher and theologian Antoine Arnauld (1612–94), the English philosopher Thomas Hobbes (1588–1679), and the EpicureanatomistPierre Gassendi (1592–1655)—as well as Descartes’s replies. The second edition (1642) includes a response by the Jesuit priest Pierre Bourdin (1595–1653), who Descartes said was a fool. These objections and replies constitute a landmark of cooperative discussion in philosophy and science at a time when dogmatism was the rule.

The Meditations is characterized by Descartes’s use of methodic doubt, a systematic procedure of rejecting as though false all types of belief in which one has ever been, or could ever be, deceived. His arguments derive from the skepticism of the Greek philosopher Sextus Empiricus (fl. 3rd century ce) as reflected in the work of the essayist Michel de Montaigne (1533–92) and the Catholic theologian Pierre Charron (1541–1603). Thus, Descartes’s apparent knowledge based on authority is set aside, because even experts are sometimes wrong. His beliefs from sensory experience are declared untrustworthy, because such experience is sometimes misleading, as when a square tower appears round from a distance. Even his beliefs about the objects in his immediate vicinity may be mistaken, because, as he notes, he often has dreams about objects that do not exist, and he has no way of knowing with certainty whether he is dreaming or awake. Finally, his apparent knowledge of simple and general truths of reasoning that do not depend on sense experience—such as “2 + 3 = 5” or “a square has four sides”—is also unreliable, because God could have made him in such a way that, for example, he goes wrong every time he counts. As a way of summarizing the universal doubt into which he has fallen, Descartes supposes that an “evil genius of the utmost power and cunning has employed all his energies in order to deceive me.”

Although at this stage there is seemingly no belief about which he cannot entertain doubt, Descartes finds certainty in the intuition that, when he is thinking—even if he is being deceived—he must exist. In the Discourse, Descartes expresses this intuition in the dictum “I think, therefore I am”; but because “therefore” suggests that the intuition is an argument—though it is not—in the Meditations he says merely, “I think, I am” (“Cogito, sum”). The cogito is a logically self-evident truth that also gives intuitively certain knowledge of a particular thing’s existence—that is, one’s self. Nevertheless, it justifies accepting as certain only the existence of the person who thinks it. If all one ever knew for certain was that one exists, and if one adhered to Descartes’s method of doubting all that is uncertain, then one would be reduced to solipsism, the view that nothing exists but one’s self and thoughts. To escape solipsism, Descartes argues that all ideas that are as “clear and distinct” as the cogito must be true, for, if they were not, the cogito also, as a member of the class of clear and distinct ideas, could be doubted. Since “I think, I am” cannot be doubted, all clear and distinct ideas must be true.

On the basis of clear and distinct innate ideas, Descartes then establishes that each mind is a mental substance and each body a part of one material substance. The mind or soul is immortal, because it is unextended and cannot be broken into parts, as can extended bodies. Descartes also advances at least two proofs for the existence of God. The final proof, presented in the Fifth Meditation, begins with the proposition that Descartes has an innate idea of God as a perfect being. It concludes that God necessarily exists, because, if he did not, he would not be perfect. This ontological argument for God’s existence, introduced by the medieval English logician St. Anselm of Canterbury (1033/34–1109), is at the heart of Descartes’s rationalism, for it establishes certain knowledge about an existing thing solely on the basis of reasoning from innate ideas, with no help from sensory experience. Descartes elsewhere argues that, because God is perfect, he does not deceive human beings, and therefore, because God leads us to believe that the material world exists, it does exist. In this way Descartes claims to establish metaphysical foundations for the existence of his own mind, of God, and of the material world.

The inherent circularity of Descartes’s reasoning was exposed by Arnauld, whose objection has come to be known as the Cartesian Circle. According to Descartes, God’s existence is established by the fact that Descartes has a clear and distinct idea of God; but the truth of Descartes’s clear and distinct ideas are guaranteed by the fact that God exists and is not a deceiver. Thus, in order to show that God exists, Descartes must assume that God exists.

Physics, physiology, and morals

Descartes’s general goal was to help human beings master and possess nature. He provided understanding of the trunk of the tree of knowledge in The World, Dioptrics, Meteorology, and Geometry, and he established its metaphysical roots in the Meditations. He then spent the rest of his life working on the branches of mechanics, medicine, and morals. Mechanics is the basis of his physiology and medicine, which in turn is the basis of his moral psychology. Descartes believed that all material bodies, including the human body, are machines that operate by mechanical principles. In his physiological studies, he dissected animal bodies to show how their parts move. He argued that, because animals have no souls, they do not think or feel; thus, vivisection, which Descartes practiced, is permitted. He also described the circulation of the blood but came to the erroneous conclusion that heat in the heart expands the blood, causing its expulsion into the veins. Descartes’s L’Homme, et un traité de la formation du foetus (Man, and a Treatise on the Formation of the Foetus) was published in 1664.

In 1644 Descartes published Principles of Philosophy, a compilation of his physics and metaphysics. He dedicated this work to Princess Elizabeth (1618–79), daughter of Elizabeth Stuart, titular queen of Bohemia, in correspondence with whom he developed his moral philosophy. According to Descartes, a human being is a union of mind and body, two radically dissimilar substances that interact in the pineal gland. He reasoned that the pineal gland must be the uniting point because it is the only nondouble organ in the brain, and double reports, as from two eyes, must have one place to merge. He argued that each action on a person’s sense organs causes subtle matter to move through tubular nerves to the pineal gland, causing it to vibrate distinctively. These vibrations give rise to emotions and passions and also cause the body to act. Bodily action is thus the final outcome of a reflex arc that begins with external stimuli—as, for example, when a soldier sees the enemy, feels fear, and flees. The mind cannot change bodily reactions directly—for example, it cannot will the body to fight—but by altering mental attitudes, it can change the pineal vibrations from those that cause fear and fleeing to those that cause courage and fighting.

Descartes argued further that human beings can be conditioned by experience to have specific emotional responses. Descartes himself, for example, had been conditioned to be attracted to cross-eyed women because he had loved a cross-eyed playmate as a child. When he remembered this fact, however, he was able to rid himself of his passion. This insight is the basis of Descartes’s defense of free will and of the mind’s ability to control the body. Despite such arguments, in his Passions of the Soul (1649), which he dedicated to Queen Christina of Sweden (reigned 1644–54), Descartes holds that most bodily actions are determined by external material causes.

Descartes’s morality is anti-Jansenist and anti-Calvinist in that he maintains that the grace that is necessary for salvation can be earned and that human beings are virtuous and able to achieve salvation when they do their best to find and act upon the truth. His optimism about the ability of human reason and will to find truth and reach salvation contrasts starkly with the pessimism of the Jansenist apologist and mathematician Blaise Pascal (1623–62), who believed that salvation comes only as a gift of God’s grace. Descartes was correctly accused of holding the view of Jacobus Arminius (1560–1609), an anti-Calvinist Dutch theologian, that salvation depends on free will and good works rather than on grace. Descartes also held that, unless people believe in God and immortality, they will see no reason to be moral.

Free will, according to Descartes, is the sign of God in human nature, and human beings can be praised or blamed according to their use of it. People are good, he believed, only to the extent that they act freely for the good of others; such generosity is the highest virtue. Descartes was Epicurean in his assertion that human passions are good in themselves. He was an extreme moral optimist in his belief that understanding of the good is automatically followed by a desire to do the good. Moreover, because passions are “willings” according to Descartes, to want something is the same as to will it. Descartes was also stoic, however, in his admonition that, rather than change the world, human beings should control their passions.

Although Descartes wrote no political philosophy, he approved of the admonition of Seneca (c. 4 bce–65 ce) to acquiesce in the common order of things. He rejected the recommendation of Niccolò Machiavelli (1469–1527) to lie to one’s friends, because friendship is sacred and life’s greatest joy. Human beings cannot exist alone but must be parts of social groups, such as nations and families, and it is better to do good for the group than for oneself.

Descartes had been a puny child with a weak chest and was not expected to live. He therefore watched his health carefully, becoming a virtual vegetarian. In 1639 he bragged that he had not been sick for 19 years and that he expected to live to 100. He told Princess Elizabeth to think of life as a comedy; bad thoughts cause bad dreams and bodily disorders. Because there is always more good than evil in life, he said, one can always be content, no matter how bad things seem. Elizabeth, inextricably involved in messy court and family affairs, was not consoled.

In his later years Descartes said that he had once hoped to learn to prolong life to a century or more, but he then saw that, to achieve that goal, the work of many generations would be required; he himself had not even learned to prevent a fever. Thus, he said, instead of continuing to hope for long life, he had found an easier way, namely to love life and not to fear death. It is easy, he claimed, for a true philosopher to die tranquilly.

Final years and heritage

In 1644, 1647, and 1648, after 16 years in the Netherlands, Descartes returned to France for brief visits on financial business and to oversee the translation into French of the Principles, the Meditations, and the Objections and Replies. (The translators were, respectively, Picot, Charles d’Albert, duke de Luynes, and Claude Clerselier.) In 1647 he also met with Gassendi and Hobbes, and he suggested to Pascal the famous experiment of taking a barometer up Mount Puy-de-Dôme to determine the influence of the weight of the air. Picot returned with Descartes to the Netherlands for the winter of 1647–48. During Descartes’s final stay in Paris in 1648, the French nobility revolted against the crown in a series of wars known as the Fronde. Descartes left precipitously on August 17, 1648, only days before the death of his old friend Mersenne.

Clerselier’s brother-in-law, Hector Pierre Chanut, who was French resident in Sweden and later ambassador, helped to procure a pension for Descartes from Louis XIV, though it was never paid. Later, Chanut engineered an invitation for Descartes to the court of Queen Christina, who by the close of the Thirty Years’ War (1618–48) had become one of the most important and powerful monarchs in Europe. Descartes went reluctantly, arriving early in October 1649. He may have gone because he needed patronage; the Fronde seemed to have destroyed his chances in Paris, and the Calvinist theologians were harassing him in the Netherlands.

In Sweden—where, Descartes said, in winter men’s thoughts freeze like the water—the 22-year-old Christina perversely made the 53-year-old Descartes rise before 5:00 am to give her philosophy lessons, even though she knew of his habit of lying in bed until 11 o’clock in the morning. She also is said to have ordered him to write the verses of a ballet, The Birth of Peace (1649), to celebrate her role in the Peace of Westphalia, which ended the Thirty Years’ War. The verses in fact were not written by Descartes, though he did write the statutes for a Swedish Academy of Arts and Sciences. While delivering these statutes to the queen at 5:00 am on February 1, 1650, he caught a chill, and he soon developed pneumonia. He died in Stockholm on February 11. Many pious last words have been attributed to him, but the most trustworthy report is that of his German valet, who said that Descartes was in a coma and died without saying anything at all.

Descartes’s papers came into the possession of Claude Clerselier, a pious Catholic, who began the process of turning Descartes into a saint by cutting, adding to, and selectively publishing his letters. This cosmetic work culminated in 1691 in the massive biography by Father Adrien Baillet, who was at work on a 17-volume Lives of the Saints. Even during Descartes’s lifetime there were questions about whether he was a Catholic apologist, primarily concerned with supporting Christian doctrine, or an atheist, concerned only with protecting himself with pious sentiments while establishing a deterministic, mechanistic, and materialistic physics.

These questions remain difficult to answer, not least because all the papers, letters, and manuscripts available to Clerselier and Baillet are now lost. In 1667 the Roman Catholic church made its own decision by putting Descartes’s works on the Index Librorum Prohibitorum (Latin: “Index of Prohibited Books”) on the very day his bones were ceremoniously placed in Sainte-Geneviève-du-Mont in Paris. During his lifetime, Protestant ministers in the Netherlands called Descartes a Jesuit and a papist—which is to say an atheist. He retorted that they were intolerant, ignorant bigots. Up to about 1930, a majority of scholars, many of whom were religious, believed that Descartes’s major concerns were metaphysical and religious. By the late 20th century, however, numerous commentators had come to believe that Descartes was a Catholic in the same way he was a Frenchman and a royalist—that is, by birth and by convention.

Descartes himself said that good sense is destroyed when one thinks too much of God. He once told a German protégée, Anna Maria van Schurman (1607–78), who was known as a painter and a poet, that she was wasting her intellect studying Hebrew and theology. He also was perfectly aware of—though he tried to conceal—the atheistic potential of his materialist physics and physiology. Descartes seemed indifferent to the emotional depths of religion. Whereas Pascal trembled when he looked into the infinite universe and perceived the puniness and misery of man, Descartes exulted in the power of human reason to understand the cosmos and to promote happiness, and he rejected the view that human beings are essentially miserable and sinful. He held that it is impertinent to pray to God to change things. Instead, when we cannot change the world, we must change ourselves.


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