Cogito ergo sum is a Latin philosophical proposition by René Descartes usually translated into English as “I think, therefore I am”. The phrase originally appeared in French as “je pense, donc je suis” in his Discourse on the Method, so as to reach a wider audience than Latin would have allowed. It appeared in Latin in his later Principles of Philosophy. As Descartes explained, “[W]e cannot doubt of our existence while we doubt… .” A fuller form, dubito, ergo cogito, ergo sum (“I doubt, therefore I think, therefore I am”), aptly captures Descartes’ intent.

This proposition became a fundamental element of Western philosophy, as it purported to form a secure foundation for knowledge in the face of radical doubt. While other knowledge could be a figment of imagination, deception, or mistake, Descartes asserted that the very act of doubting one’s own existence served – at minimum – as proof of the reality of one’s own mind; there must be a thinking entity – in this case the self – for there to be a thought.

Luc Paquin

I Think, Therefore I Am

While methodic doubt has a nature, one need not hold that knowledge is impossible in order to apply the method of doubt. Indeed, Descartes’ attempt to apply the method of doubt to the existence of himself spawned the proof of his famous saying, “Cogito ergo sum” (I think, therefore I am). That is, Descartes tried to doubt his own existence, but found that even his doubting showed that he existed, since he could not doubt if he did not exist.

Criticisms

Cartesian skepticism advocates the doubting of all things which cannot be justified through logic. Some have claimed that the corresponding philosophical proposition fails the criterion of falsifiability that is associated with empirical theory.

Incontrovertible Evidence

Incontrovertible evidence is a colloquial term for evidence introduced to prove a fact that is supposed to be so conclusive that there can be no other truth as to the matter; evidence so strong it overpowers contrary evidence, directing a fact-finder to a specific and certain conclusion.

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Descartes’ Method

René Descartes, the originator of Cartesian doubt, put all beliefs, ideas, thoughts, and matter in doubt. He showed that his grounds, or reasoning, for any knowledge could just as well be false. Sensory experience, the primary mode of knowledge, is often erroneous and therefore must be doubted. For instance, what one is seeing may very well be a hallucination. There is nothing that proves it cannot be. In short, if there is any way a belief can be disproved, then its grounds are insufficient. From this, Descartes proposed two arguments, the dream and the demon.

The Dream Argument

Descartes, knowing that the context of our dreams, while possibly unbelievable, are often lifelike, hypothesized that humans can only believe that they are awake. There are no sufficient grounds by which to distinguish a dream experience from a waking experience. For instance, subject a sits at the computer, typing this article. Just as much evidence exists to indicate that the act of composing this article is reality, as there is evidence to demonstrate the opposite. Descartes conceded that we live in a world that can create such ideas as dreams. However, by the end of The Meditations, he concludes that we can distinguish dream from reality at least in retrospect.

The Evil Demon

Descartes reasoned that our very own experience may very well be controlled by an evil demon of sorts. This genius is as clever and deceitful as he is powerful. He could have created a superficial world that we may think we live in.

In Meditation I, Descartes stated that if one were mad, even briefly, the insanity might have driven man into believing that what we thought was true could be merely our minds deceiving us. He also stated that there could be ‘some malicious, powerful, cunning demon’ that had deceived us, preventing us from judging correctly.

Descartes argued that all his senses were lying and since your senses can easily fool you, his idea of an infinitely powerful being must be true as that idea could have only been put there by an infinitely powerful being which would have no reason to be deceitful to him.

Luc Paquin

Cartesian doubt is a form of methodological skepticism or scepticism associated with the writings and methodology of René Descartes (1596-1650). Cartesian doubt is also known as Cartesian skepticism, methodic doubt, methodological skepticism, Universal Doubt, or hyperbolic doubt.

Cartesian doubt is a systematic process of being skeptical about (or doubting) the truth of one’s beliefs, which has become a characteristic method in philosophy. This method of doubt was largely popularized in Western philosophy by René Descartes, who sought to doubt the truth of all his beliefs in order to determine which beliefs he could be certain were true.

Methodological skepticism is distinguished from philosophical skepticism in that methodological skepticism is an approach that subjects all knowledge claims to scrutiny with the goal of sorting out true from false claims, whereas philosophical skepticism is an approach that questions the possibility of pure knowledge.

Characteristics

Cartesian doubt is methodological. Its purpose is to use doubt as a route to certain knowledge by finding those things which could not be doubted. The fallibility of sense data in particular is a subject of Cartesian doubt.

There are several interpretations as to the objective of Descartes’ skepticism. Prominent among these is a foundationalist account which claims that Descartes’ skepticism is aimed at eliminating all belief which it is possible to doubt, thus leaving Descartes with only basic beliefs (also known as foundational beliefs). From these indubitable basic beliefs, Descartes then attempts to derive further knowledge. It’s an archetypal and significant example that epitomizes the Continental Rational schools of philosophy.

Technique

Descartes’ Method

• 1. Accepting only information you know to be true
• 2. Breaking down these truths into smaller units
• 3. Solving the simple problems first
• 4. Making complete lists of further problems

Is also known as hyperbolic doubt or having the tendency to doubt, since it is an extreme or exaggerated form of doubt. (Knowledge in the Cartesian sense means to know something beyond not merely all reasonable, but all possible, doubt.) In his Meditations on First Philosophy (1641), Descartes resolved to systematically doubt that any of his beliefs were true, in order to build, from the ground up, a belief system consisting of only certainly true beliefs. Consider Descartes’ opening lines of the Meditations:

• Several years have now elapsed since I first became aware that I had accepted, even from my youth, many false opinions for true, and that consequently what I afterward based on such principles was highly doubtful; and from that time I was convinced of the necessity of undertaking once in my life to rid myself of all the opinions I had adopted, and of commencing anew the work of building from the foundation…

  – René Descartes , Meditation I, 1641

Luc Paquin

Cartesianism is the name given to the philosophical doctrine (or school) of René Descartes. Descartes is often regarded as the first thinker to emphasize the use of reason to develop the natural sciences. For him, the philosophy was a thinking system that embodied all knowledge, and expressed it in this way:

Cartesians view the mind as being wholly separate from the corporeal body. Sensation and the perception of reality are thought to be the source of untruth and illusions, with the only reliable truths to be had in the existence of a metaphysical mind. Such a mind can perhaps interact with a physical body, but it does not exist in the body, nor even in the same physical plane as the body.

In general, Cartesian thought divides the world into three areas of existence:

• That inhabited by the physical body (matter),
• That inhabited by the mind, and
• That inhabited by God.

Geographical Dispersal

In The Netherlands, where Descartes had lived for a long time, Cartesianism was a doctrine popular mainly among university professors and lecturers. In Germany the influence of this doctrine was not relevant and followers of Cartesianism in the German-speaking border regions between these countries (e.g., the iatromathematician Yvo Gaukes from East Frisia) frequently chose to publish their works in The Netherlands. In France, it was very popular, and gained influence also among Jansenists such as Antoine Arnauld, though there also, as in Italy, it became opposed by the Church. In Italy, the doctrine failed to make inroads, probably since Descartes’ works were placed on the Index Librorum Prohibitorum in 1663.

In England, because of religious and other reasons, Cartesianism was not widely accepted. Though Henry More was initially attracted to the doctrine, his own changing attitudes toward Descartes mirrored those of the country: “quick acceptance, serious examination with accumulating ambivalence, final rejection.”

Notable Cartesians

• Antoine Arnauld
• Balthasar Bekker
• Johannes Clauberg
• Michelangelo Fardella
• Antoine Le Grand
• Adriaan Hereboord
• Nicolas Malebranche
• François Poullain de la Barre
• Edmond Pourchot
• Pierre-Sylvain Régis
• Henricus Regius
• Jacques Rohault
• Christopher Wittich

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Writings

• 1618. Musicae Compendium. A treatise on music theory and the aesthetics of music written for Descartes’ early collaborator, Isaac Beeckman (first posthumous edition 1650).
• 1626-1628. Regulae ad directionem ingenii (Rules for the Direction of the Mind). Incomplete. First published posthumously in Dutch translation in 1684 and in the original Latin at Amsterdam in 1701 (R. Des-Cartes Opuscula Posthuma Physica et Mathematica). The best critical edition, which includes the Dutch translation of 1684, is edited by Giovanni Crapulli (The Hague: Martinus Nijhoff, 1966).
• 1630-1631. La recherche de la vérité par la lumière naturelle (The Search for Truth) unfinished dialogue published in 1701.
• 1630-1633. Le Monde (The World) and L’Homme (Man). Descartes’ first systematic presentation of his natural philosophy. Man was published posthumously in Latin translation in 1662; and The World posthumously in 1664.
• 1637. Discours de la méthode (Discourse on the Method). An introduction to the Essais, which include the Dioptrique, the Météores and the Géométrie.
• 1637. La Géométrie (Geometry). Descartes’ major work in mathematics. There is an English translation by Michael Mahoney (New York: Dover, 1979).
• 1641. Meditationes de prima philosophia (Meditations on First Philosophy), also known as Metaphysical Meditations. In Latin; a French translation, probably done without Descartes’ supervision, was published in 1647. Includes six Objections and Replies. A second edition, published the following year, included an additional objection and reply, and a Letter to Dinet.
• 1644. Principia philosophiae (Principles of Philosophy), a Latin textbook at first intended by Descartes to replace the Aristotelian textbooks then used in universities. A French translation, Principes de philosophie by Claude Picot, under the supervision of Descartes, appeared in 1647 with a letter-preface to Princess Elisabeth of Bohemia.
• 1647. Notae in programma (Comments on a Certain Broadsheet). A reply to Descartes’ one-time disciple Henricus Regius.
• 1648. La description du corps humaine (The Description of the Human Body). Published posthumously by Clerselier in 1667.
• 1648. Responsiones Renati Des Cartes… (Conversation with Burman). Notes on a Q&A session between Descartes and Frans Burman on 16 April 1648. Rediscovered in 1895 and published for the first time in 1896. An annotated bilingual edition (Latin with French translation), edited by Jean-Marie Beyssade, was published in 1981 (Paris: PUF).
• 1649. Les passions de l’âme (Passions of the Soul). Dedicated to Princess Elisabeth of the Palatinate.
• 1657. Correspondance. Published by Descartes’ literary executor Claude Clerselier. The third edition, in 1667, was the most complete; Clerselier omitted, however, much of the material pertaining to mathematics.

In January 2010, a previously unknown letter from Descartes, dated 27 May 1641, was found by the Dutch philosopher Erik-Jan Bos when browsing through Google. Bos found the letter mentioned in a summary of autographs kept by Haverford College in Haverford, Pennsylvania. The College was unaware that the letter had never been published. This was the third letter by Descartes found in the last 25 years.

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Historical Impact

Emancipation from Church Doctrine

Descartes has often been dubbed the father of modern Western philosophy, the philosopher that with his skeptic approach has profoundly changed the course of Western philosophy and set the basis for modernity. The first two of his Meditations on First Philosophy, those that formulate the famous methodic doubt, represent the portion of Descartes’ writings that most influenced modern thinking. It has been argued that Descartes himself didn’t realize the extent of his revolutionary gesture. In shifting the debate from “what is true” to “of what can I be certain?,” Descartes shifted the authoritative guarantor of truth from God to humanity. (While the traditional concept of “truth” implies an external authority, “certainty” instead relies on the judgment of the individual.) In an anthropocentric revolution, the human being is now raised to the level of a subject, an agent, an emancipated being equipped with autonomous reason. This was a revolutionary step that posed the basis of modernity, the repercussions of which are still ongoing: the emancipation of humanity from Christian revelational truth and Church doctrine, a person who makes his own law and takes his own stand. In modernity, the guarantor of truth is not God anymore but human beings, each of whom is a “self-conscious shaper and guarantor” of their own reality. In that way, each person is turned into a reasoning adult, a subject, and agent, as opposed to a child obedient to God. This change in perspective was characteristic of the shift from the Christian medieval period to the modern period; that shift had been anticipated in other fields, and now Descartes was giving it a formulation in the field of philosophy.

This anthropocentric perspective, establishing human reason as autonomous, provided the basis for the Enlightenment’s emancipation from God and the Church. It also provided the basis for all subsequent anthropology. Descartes’ philosophical revolution is sometimes said to have sparked modern anthropocentrism and subjectivism.

Mathematical Legacy

One of Descartes’ most enduring legacies was his development of Cartesian or analytic geometry, which uses algebra to describe geometry. He “invented the convention of representing unknowns in equations by x, y, and z, and knowns by a, b, and c”. He also “pioneered the standard notation” that uses superscripts to show the powers or exponents; for example, the 4 used in x4 to indicate squaring of squaring. He was first to assign a fundamental place for algebra in our system of knowledge, and believed that algebra was a method to automate or mechanize reasoning, particularly about abstract, unknown quantities. European mathematicians had previously viewed geometry as a more fundamental form of mathematics, serving as the foundation of algebra. Algebraic rules were given geometric proofs by mathematicians such as Pacioli, Cardan, Tartaglia and Ferrari. Equations of degree higher than the third were regarded as unreal, because a three-dimensional form, such as a cube, occupied the largest dimension of reality. Descartes professed that the abstract quantity a2 could represent length as well as an area. This was in opposition to the teachings of mathematicians, such as Vieta, who argued that it could represent only area. Although Descartes did not pursue the subject, he preceded Leibniz in envisioning a more general science of algebra or “universal mathematics,” as a precursor to symbolic logic, that could encompass logical principles and methods symbolically, and mechanize general reasoning.

Descartes’ work provided the basis for the calculus developed by Newton and Gottfried Leibniz, who applied infinitesimal calculus to the tangent line problem, thus permitting the evolution of that branch of modern mathematics. His rule of signs is also a commonly used method to determine the number of positive and negative roots of a polynomial.

Descartes discovered an early form of the law of conservation of mechanical momentum (a measure of the motion of an object), and envisioned it as pertaining to motion in a straight line, as opposed to perfect circular motion, as Galileo had envisioned it. He outlined his views on the universe in his Principles of Philosophy.

Descartes also made contributions to the field of optics. He showed by using geometric construction and the law of refraction (also known as Descartes’ law or more commonly Snell’s law) that the angular radius of a rainbow is 42 degrees (i.e., the angle subtended at the eye by the edge of the rainbow and the ray passing from the sun through the rainbow’s centre is 42°). He also independently discovered the law of reflection, and his essay on optics was the first published mention of this law.

Influence on Newton’s Mathematics

Current opinion is that Descartes had the most influence of anyone on the young Newton, and this is arguably one of Descartes’ most important contributions. Newton continued Descartes’ work on cubic equations, which freed the subject from the fetters of the Greek and Macedonian perspectives. The most important concept was his very modern treatment of independent variables.

Contemporary Reception

Although Descartes was well known in academic circles towards the end of his life, the teaching of his works in schools was controversial. Henri de Roy (Henricus Regius, 1598-1679), Professor of Medicine at the University of Utrecht, was condemned by the Rector of the University, Gijsbert Voet (Voetius), for teaching Descartes’ physics.

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Philosophical Work

Descartes’ Moral Philosophy

For Descartes, ethics was a science, the highest and most perfect of them. Like the rest of the sciences, ethics had its roots in metaphysics. In this way he argues for the existence of God, investigates the place of man in nature, formulates the theory of mind-body dualism, and defends free will. However, as he was a convinced rationalist, Descartes clearly states that reason is sufficient in the search for the goods that we should seek, and virtue consists in the correct reasoning that should guide our actions. Nevertheless, the quality of this reasoning depends on knowledge, because a well-informed mind will be more capable of making good choices, and it also depends on mental condition. For this reason he said that a complete moral philosophy should include the study of the body. He discussed this subject in the correspondence with Princess Elisabeth of Bohemia, and as a result wrote his work The Passions of the Soul, that contains a study of the psychosomatic processes and reactions in man, with an emphasis on emotions or passions.

Humans should seek the sovereign good that Descartes, following Zeno, identifies with virtue, as this produces a solid blessedness or pleasure. For Epicurus the sovereign good was pleasure, and Descartes says that in fact this is not in contradiction with Zeno’s teaching, because virtue produces a spiritual pleasure, that is better than bodily pleasure. Regarding Aristotle’s opinion that happiness depends on the goods of fortune, Descartes does not deny that this good contributes to happiness, but remarks that they are in great proportion outside one’s own control, whereas one’s mind is under one’s complete control.

The moral writings of Descartes came at the last part of his life, but earlier, in his Discourse on the Method he adopted three maxims to be able to act while he put all his ideas into doubt. This is known as his “Provisional Morals”.

Religious Beliefs

In his “Meditations on First Philosophy” Descartes sets forth two proofs for God’s existence. One of these is founded upon the possibility of thinking the “idea of a being that is supremely perfect and infinite,” and suggests that “of all the ideas that are in me, the idea that I have of God is the most true, the most clear and distinct.” Descartes considered himself to be a devout Catholic, and one of the purposes of the Meditations was to defend the Christian faith. His attempt to ground theological beliefs on reason encountered intense opposition in his time, however: Pascal regarded Descartes’ views as rationalist and mechanist, and accused him of deism: “I cannot forgive Descartes; in all his philosophy, Descartes did his best to dispense with God. But Descartes could not avoid prodding God to set the world in motion with a snap of his lordly fingers; after that, he had no more use for God,” while a powerful contemporary, Martin Schoock, accused him of atheist beliefs, though Descartes had provided an explicit critique of atheism in his Meditations. The Catholic Church prohibited his books in 1663.

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Philosophical Work

Dualism

Descartes in his Passions of the Soul and The Description of the Human Body suggested that the body works like a machine, that it has material properties. The mind (or soul), on the other hand, was described as a nonmaterial and does not follow the laws of nature. Descartes argued that the mind interacts with the body at the pineal gland. This form of dualism or duality proposes that the mind controls the body, but that the body can also influence the otherwise rational mind, such as when people act out of passion. Most of the previous accounts of the relationship between mind and body had been uni-directional.

Descartes suggested that the pineal gland is “the seat of the soul” for several reasons. First, the soul is unitary, and unlike many areas of the brain the pineal gland appeared to be unitary (though subsequent microscopic inspection has revealed it is formed of two hemispheres). Second, Descartes observed that the pineal gland was located near the ventricles. He believed the cerebrospinal fluid of the ventricles acted through the nerves to control the body, and that the pineal gland influenced this process. Sensations delivered by the nerves to the pineal, he believed, caused it to vibrate in some sympathetic manner, which in turn gave rise to the emotions and caused the body to act. Cartesian dualism set the agenda for philosophical discussion of the mind-body problem for many years after Descartes’ death.

In present day discussions on the practice of animal vivisection, it is normal to consider Descartes as an advocate of this practice, as a result of his dualistic philosophy. Some of the sources say that Descartes denied the animals could feel pain, and therefore could be used without concern. Other sources consider that Descartes denied that animals had reason or intelligence, but did not lack sensations or perceptions, but these could be explained mechanistically.

Luc Paquin

Philosophical Work

Descartes is often regarded as the first thinker to emphasize the use of reason to develop the natural sciences. For him the philosophy was a thinking system that embodied all knowledge, and expressed it in this way:

• Thus, all Philosophy is like a tree, of which Metaphysics is the root, Physics the trunk, and all the other sciences the branches that grow out of this trunk, which are reduced to three principals, namely, Medicine, Mechanics, and Ethics. By the science of Morals, I understand the highest and most perfect which, presupposing an entire knowledge of the other sciences, is the last degree of wisdom.

In his Discourse on the Method, he attempts to arrive at a fundamental set of principles that one can know as true without any doubt. To achieve this, he employs a method called hyperbolical/metaphysical doubt, also sometimes referred to as methodological skepticism: he rejects any ideas that can be doubted, and then reestablishes them in order to acquire a firm foundation for genuine knowledge.

Initially, Descartes arrives at only a single principle: thought exists. Thought cannot be separated from me, therefore, I exist (Discourse on the Method and Principles of Philosophy). Most famously, this is known as cogito ergo sum (English: “I think, therefore I am”). Therefore, Descartes concluded, if he doubted, then something or someone must be doing the doubting, therefore the very fact that he doubted proved his existence. “The simple meaning of the phrase is that if one is skeptical of existence, that is in and of itself proof that he does exist.”

Descartes concludes that he can be certain that he exists because he thinks. But in what form? He perceives his body through the use of the senses; however, these have previously been unreliable. So Descartes determines that the only indubitable knowledge is that he is a thinking thing. Thinking is what he does, and his power must come from his essence. Descartes defines “thought” (cogitatio) as “what happens in me such that I am immediately conscious of it, insofar as I am conscious of it”. Thinking is thus every activity of a person of which the person is immediately conscious.

To further demonstrate the limitations of these senses, Descartes proceeds with what is known as the Wax Argument. He considers a piece of wax; his senses inform him that it has certain characteristics, such as shape, texture, size, color, smell, and so forth. When he brings the wax towards a flame, these characteristics change completely. However, it seems that it is still the same thing: it is still the same piece of wax, even though the data of the senses inform him that all of its characteristics are different. Therefore, in order to properly grasp the nature of the wax, he should put aside the senses. He must use his mind. Descartes concludes:

• And so something that I thought I was seeing with my eyes is in fact grasped solely by the faculty of judgment which is in my mind.

In this manner, Descartes proceeds to construct a system of knowledge, discarding perception as unreliable and instead admitting only deduction as a method. In the third and fifth Meditation, he offers an ontological proof of a benevolent God (through both the ontological argument and trademark argument). Because God is benevolent, he can have some faith in the account of reality his senses provide him, for God has provided him with a working mind and sensory system and does not desire to deceive him. From this supposition, however, he finally establishes the possibility of acquiring knowledge about the world based on deduction and perception. In terms of epistemology therefore, he can be said to have contributed such ideas as a rigorous conception of foundationalism and the possibility that reason is the only reliable method of attaining knowledge. He, nevertheless, was very much aware that experimentation was necessary in order to verify and validate theories.

Descartes also wrote a response to External world scepticism. He argues that sensory perceptions come to him involuntarily, and are not willed by him. They are external to his senses, and according to Descartes, this is evidence of the existence of something outside of his mind, and thus, an external world. Descartes goes on to show that the things in the external world are material by arguing that God would not deceive him as to the ideas that are being transmitted, and that God has given him the “propensity” to believe that such ideas are caused by material things. He gave reasons for thinking that waking thoughts are distinguishable from dreams, and that one’s mind cannot have been “hijacked” by an evil demon placing an illusory external world before one’s senses.

Luc Paquin