Cartesian circle

Last updated

The Cartesian circle is a potential mistake in reasoning attributed to René Descartes.

René Descartes 17th-century French philosopher, mathematician, and scientist

René Descartes was a French philosopher, mathematician, and scientist. A native of the Kingdom of France, he spent about 20 years (1629–1649) of his life in the Dutch Republic after serving for a while in the Dutch States Army of Maurice of Nassau, Prince of Orange and the Stadtholder of the United Provinces. He is generally considered one of the most notable intellectual figures of the Dutch Golden Age.


Descartes argues – for example, in the third of his Meditations on First Philosophy – that whatever one clearly and distinctly perceives is true: "I now seem to be able to lay it down as a general rule that whatever I perceive very clearly and distinctly is true." (AT VII 35) [1] He goes on in the same Meditation to argue for the existence of a benevolent God, in order to defeat his skeptical argument in the first Meditation that God might be a deceiver. He then says that without his knowledge of God's existence, none of his knowledge could be certain.

<i>Meditations on First Philosophy</i> philosophy book by Descartes

Meditations on First Philosophy in which the existence of God and the immortality of the soul are demonstrated is a philosophical treatise by René Descartes first published in Latin in 1641. The French translation was published in 1647 as Méditations Métaphysiques. The title may contain a misreading by the printer, mistaking animae immortalitas for animae immaterialitas, as suspected by A. Baillet.

The Cartesian circle is a criticism of the above that takes this form:

  1. Descartes' proof of the reliability of clear and distinct perceptions takes as a premise God's existence as a non-deceiver.
  2. Descartes' proofs of God's existence presuppose the reliability of clear and distinct perceptions.

Thus, Descartes' argument is circular.

Descartes' contemporaries

Many commentators, both at the time that Descartes wrote and since, have argued that this involves a circular argument, as he relies upon the principle of clarity and distinctness to argue for the existence of God, and then claims that God is the guarantor of his clear and distinct ideas. The first person to raise this criticism was Marin Mersenne, in the "Second Set of Objections" to the Meditations:

The existence of God is a subject of debate in the philosophy of religion and popular culture.

Marin Mersenne French theologian, philosopher, mathematician and music theorist, often referred to as the "father of acoustics"

Marin Mersenne, Marin Mersennus or le PèreMersenne was a French polymath, whose works touched a wide variety of fields. He is perhaps best known today among mathematicians for Mersenne prime numbers, those which can be written in the form Mn = 2n − 1 for some integer n. He also developed Mersenne's laws, which describe the harmonics of a vibrating string, and his seminal work on music theory, Harmonie universelle, for which he is referred to as the "father of acoustics". Mersenne, an ordained priest, had many contacts in the scientific world and has been called "the center of the world of science and mathematics during the first half of the 1600s" and, because of his ability to make connections between people and ideas, "the post-box of Europe". He was also a member of the Minim religious order and wrote and lectured on theology and philosophy.

"you are not yet certain of the existence of God, and you say that you are not certain of anything. It follows from this that you do not yet clearly and distinctly know that you are a thinking thing, since, on your own admission, that knowledge depends on the clear knowledge of an existing God; and this you have not proved in the passage where you draw the conclusion that you clearly know what you are." (AT VII 124–125)

Logical consequence is a fundamental concept in logic, which describes the relationship between statements that hold true when one statement logically follows from one or more statements. A valid logical argument is one in which the conclusion is entailed by the premises, because the conclusion is the consequence of the premises. The philosophical analysis of logical consequence involves the questions: In what sense does a conclusion follow from its premises? and What does it mean for a conclusion to be a consequence of premises? All of philosophical logic is meant to provide accounts of the nature of logical consequence and the nature of logical truth.

Descartes' own response to this criticism, in his "Author's Replies to the Fourth Set of Objections", is first to give what has become known as the Memory response; [2] he points out that in the fifth Meditation (at AT VII 69–70) he did not say that he needed God to guarantee the truth of his clear and distinct ideas, only to guarantee his memory:

"when I said that we can know nothing for certain until we are aware that God exists, I expressly declared that I was speaking only of knowledge of those conclusions which can be recalled when we are no longer attending to the arguments by means of which we deduced them." (AT VII 140)

Secondly, he explicitly denies that the cogito is an inference: "When someone says 'I am thinking, therefore I am, or I exist' he does not deduce existence from thought by means of a syllogism, but recognizes it as something self-evident by a simple intuition of the mind." (AT VII 140) Finally, he points out that the certainty of clear and distinct ideas does not depend upon God's guarantee (AT VII 145–146). The cogito in particular is self-verifying, indubitable, immune to the strongest doubt.

A syllogism is a kind of logical argument that applies deductive reasoning to arrive at a conclusion based on two or more propositions that are asserted or assumed to be true.

Modern commentators

Bernard Williams presents the memory defense as follows: "When one is actually intuiting a given proposition, no doubt can be entertained. So any doubt there can be must be entertained when one is not intuiting the proposition." (p. 206) He goes on to argue: "The trouble with Descartes's system is not that it is circular; nor that there is an illegitimate relation between the proofs of God and the clear and distinct perceptions [...] The trouble is that the proofs of God are invalid and do not convince even when they are supposedly being intuited". (p. 210)

As Andrea Christofidou explains:

"The distinction appropriate here is that between cognitio and scientia; both are true and cannot be contradicted, but the latter is objectively true and certain (with the guarantee of God), while the former is subjectively true and certain, that is, time-bound, and objectively possible (and does not need the guarantee of God)." (pp 219–220)

A more interesting defense of Descartes against the charge of circularity is developed by Harry Frankfurt in his book Demons, Dreamers, and Madmen: the Defense of Reason in Descartes' Meditations (Bobbs–Merrill, 1970; reprinted by Princeton University Press, 2007). Frankfurt suggests that Descartes' arguments for the existence of God, and for the reliability of reason, are not intended to prove that their conclusions are absolutely true, but to show that reason can be compelled to accept them, even in the face of radical skeptical arguments. In fact, according to Frankfurt, the validation of reason is accomplished by the rejection of the main sceptical hypothesis, which is the first real (albeit negative) conclusion of the argument, whilst the proposition about God's existence is a merely preparatory step. It must be conceded that once reached the real conclusion of the argument, the Cartesian method would forbid the sceptic to reply that perhaps the cartesian proof was suggested to the meditator by the evil genius itself, in the first place (thereby accusing Descartes of vicious circularity). This accusation fails, since it requires the evil genius' existence to be still deemed (at least) a possibility – an idea which precisely, after the expanded "God's proof" the meditator has acquired a specific reason to reject.

However, according to Frankfurt the proof presupposes the validity of the principle of non-contradiction, since otherwise an argument leading to the (provisional) conclusion that a benevolent God exists, wouldn't force Descartes to reject the possible existence of the demon. Thus the proof might, after all, beg the question against a kind of skepticism radical enough to put in doubt the rule of non-contradiction.

Moreover, according to Frankfurt's Descartes, the meditator feels forced to accept his conclusion merely because of the evidence of the supporting argument, while Frankfurt himself started by explaining that the radical doubt is meant to be a criticism of evidence as a criterion of truth (even subjective truth, if you want). As Frankfurt pointed out, it seems hard to deny that the general proposition "evident statements can be false or misleading" can be thought without hindrance, and that Descartes seems to have countenanced this kind of doubt, when close to the end of the First Meditation he wrote that

" I sometimes think that others are in error respecting matters of which they believe themselves to possess a perfect knowledge, how do I know that I am not also deceived each time I add together two and three, or number the sides of a square, or form some judgment still more simple, if more simple indeed can be imagined?"

The outcome seems to be that a doubt aimed at evident ideas is supposed by Frankfurt to be overcome by means of a further evident idea, thereby begging the question.

See also


  1. "AT" refers to Oeuvres de Descartes, ed. by Charles Adam and Paul Tannery.
  2. "The Cartesian Circle". Retrieved 2017-10-09.

Related Research Articles

<i>Cogito, ergo sum</i> philosophical proposition by René Descartes

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, "we cannot doubt of our existence while we doubt...." A fuller version, articulated by Antoine Léonard Thomas, aptly captures Descartes's intent: dubito, ergo cogito, ergo sum. The concept is also sometimes known as the cogito.

Epistemology A branch of philosophy concerned with the nature and scope of knowledge

Epistemology is the branch of philosophy concerned with the theory of knowledge.

Foundationalism concerns philosophical theories of knowledge resting upon justified belief, or some secure foundation of certainty such as a conclusion inferred from a basis of sound premises. The main rival of the foundationalist theory of justification is the coherence theory of justification, whereby a body of knowledge, not requiring a secure foundation, can be established by the interlocking strength of its components, like a puzzle solved without prior certainty that each small region was solved correctly.

In philosophy, rationalism is the epistemological view that "regards reason as the chief source and test of knowledge" or "any view appealing to reason as a source of knowledge or justification". More formally, rationalism is defined as a methodology or a theory "in which the criterion of the truth is not sensory but intellectual and deductive".

<i>Discourse on the Method</i> book by Descartes

Discourse on the Method of Rightly Conducting One's Reason and of Seeking Truth in the Sciences is a philosophical and autobiographical treatise published by René Descartes in 1637. It is best known as the source of the famous quotation "Je pense, donc je suis", which occurs in Part IV of the work. A similar argument, without this precise wording, is found in Meditations on First Philosophy (1641), and a Latin version of the same statement Cogito, ergo sum is found in Principles of Philosophy (1644).

Simulated reality is the hypothesis that reality could be simulated—for example by quantum computer simulation—to a degree indistinguishable from "true" reality. It could contain conscious minds which may or may not be fully aware that they are living inside a simulation. This is quite different from the current, technologically achievable concept of virtual reality. Virtual reality is easily distinguished from the experience of actuality; participants are never in doubt about the nature of what they experience. Simulated reality, by contrast, would be hard or impossible to separate from "true" reality. There has been much debate over this topic, ranging from philosophical discourse to practical applications in computing.

<i>Critique of Pure Reason</i> 1781 book by Immanuel Kant

The Critique of Pure Reason is a 1781 book by the German philosopher Immanuel Kant, in which the author seeks to determine the limits and scope of metaphysics. A heavily-revised second edition was published in 1787. Also referred to as Kant's "First Critique", it was followed by the Critique of Practical Reason (1788) and the Critique of Judgment (1790). In the preface to the first edition, Kant explains that by a "critique of pure reason" he means not "a critique of books and systems, but of the faculty of reason in general, in respect of all knowledge after which it may strive independently of all experience" and that he aims to reach a decision about "the possibility or impossibility of metaphysics". The First Critique is often viewed as culminating several centuries of early-modern philosophy, and inaugurating modern philosophy.

The identity of indiscernibles is an ontological principle that states that there cannot be separate objects or entities that have all their properties in common. That is, entities x and y are identical if every predicate possessed by x is also possessed by y and vice versa; to suppose two things indiscernible is to suppose the same thing under two names. It states that no two distinct things can be exactly alike, but this is intended as a metaphysical principle rather than one of natural science. A related principle is the indiscernibility of identicals, discussed below.

Evil demon concept in Cartesian philosophy

The evil demon, also known as malicious demon and evil genius, is a concept in Cartesian philosophy. In the first of his 1641 Meditations on First Philosophy, Descartes imagines that an evil demon, of "utmost power and cunning has employed all his energies in order to deceive me." This evil demon is imagined to present a complete illusion of an external world, so that Descartes can say, "I shall think that the sky, the air, the earth, colours, shapes, sounds and all external things are merely the delusions of dreams which he has devised to ensnare my judgement. I shall consider myself as not having hands or eyes, or flesh, or blood or senses, but as falsely believing that I have all these things."

Certainty is perfect knowledge that has total security from error, or the mental state of being without doubt.

In philosophy, the Cartesian Self, part of a thought experiment, is an individual's mind, separate from the body and the outside world, thinking about itself and its existence. It is distinguished from the Cartesian Other, anything other than the Cartesian self. According to the philosopher Rene Descartes, there is a divide intrinsic to consciousness, such that one cannot ever bridge the space between one's own consciousness and that of another.

Infallibilism, in epistemology, is the idea that propositional knowledge is incompatible with a chance of being wrong, where this is typically understood as one's evidence or justification providing one's belief with such strong grounds that it must be true and perhaps cannot be rationally doubted. Other beliefs may be rationally justified, but they do not rise to the level of knowledge unless absolutely certain given one's evidence. Infallibilism's opposite, fallibilism, is the position that a justified true belief may be considered knowledge, even if one's evidence does not guarantee its truth, or can, given one's evidence, rationally doubt it.

Trademark argument

The trademark argument is an a priori argument for the existence of God developed by French philosopher and mathematician, René Descartes.

Cartesianism philosophical and scientific system of René Descartes

Cartesianism is the philosophical and scientific system of René Descartes and its subsequent development by other seventeenth century thinkers, most notably Nicolas Malebranche and Baruch Spinoza. 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:

Cartesian doubt form of methodological skepticism associated with the writings and methodology of René Descartes

Cartesian doubt is a form of methodological skepticism 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, systematic doubt or hyperbolic doubt.

Philosophy of Baruch Spinoza

Spinoza's philosophy encompasses nearly every area of philosophical discourse, including metaphysics, epistemology, political philosophy, ethics, philosophy of mind, and philosophy of science. It earned Spinoza an enduring reputation as one of the most important and original thinkers of the seventeenth century.

An ontological argument is a philosophical argument for the existence of God that uses ontology. Many arguments fall under the category of the ontological, and they tend to involve arguments about the state of being or existing. More specifically, ontological arguments tend to start with a priori theory about the organization of the universe. If that organizational structure is true, the argument will provide reasons why God must exist.