A Christian Response to Descartes’ Radical Doubt

Modern philosophy is said to begin with René Descartes (1596-1650; Copleston, 1994, 4:1). Many think that “René Descartes is perhaps the single most important thinker of the European Enlightenment” (Hooker, 2009; cf. Copleston, 4:174ff.). Descartes is thought to be “the father of the subjective and idealistic (as was Bacon of the objective and realistic) tradition in modern philosophy,” who “began the great game of epistemology, which in [sic] Leibniz, Locke, Berkeley, Hume and Kant waxed into a Three Hundred Years’ War that at once stimulated and devastated modern philosophy” (Durant, 1926, pp. 116,117, parenthetical item in orig.; cf. p. 268). First, I will summarize the historical/philosophical context of Descartes’ work, which will provide two things: (1) An overview of his motivations, and (2) an explanation of why the Christian apologist should be prepared to counter certain of Descartes’ arguments. Second, I will examine the nature of Descartes’ doubt, which is central to his philosophy. Finally, I will offer a critique from the Christian perspective.


Burnham and Fieser observed: “Descartes’ philosophy developed in the context of the key features of Renaissance and early modern philosophy. Like the humanists, he rejected religious authority in the quest for scientific and philosophical knowledge” (see Kenny, 1968, p. 4; cf. Maritain, 1944, p. 55). Descartes was a devout Catholic, but was influenced by the Reformation’s challenge to Church authority and scholastic Aristotelianism (philosophy in the tradition of Aristotle’s thought; “René…,” 2008). Specifically, he was influenced by the scientific ideas of Leonardo da Vinci and Galileo Galilei (see Durant, 1926, p. 117). In 1633, the Catholic church condemned Galileo’s Dialogue because of its heliocentricity, and Descartes thought that his forthcoming work, Le Monde, would offend the church as well, so he postponed its publication (Galilei, 2001; “René…”; Fowler, 1996; Rodis-Lewis, 1992, p. 39; cf. Kenny, pp. 7-8). In fact, Descartes’ first major writing was published anonymously (see Cottingham, 1986, p.13).

In developing his rationalistic philosophy, Descartes positioned himself against scholasticism and Aristotelianism, as he explains in a letter to Voetius:

[T]he philosophy against which you rail with such violence…aims at the knowledge of the truths which are acquired by means of the natural light, and which promise the benefit of the human race; by contrast the dominant philosophy, which is taught in the schools and universities, is merely a muddled collection of opinions which are mostly open to doubts, as is proved by the debates that they occasion day after day, and which are entirely without practical benefit, as centuries of experience have proved only too well (quoted in Cottingham, p. 15; cf. Copleston, p. 174).

Descartes hoped that philosophy could be as certain as mathematics, the principles of which he saw as being exceptionally sound (1952a, 31:ix; 1952b, 31:14,31; cf. Loeb, 1992, p. 219; Rodis-Lewis, 1992, pp. 26ff.; Ree, 1975, pp. 28-34), and that his writings could replace traditional texts based on Aristotle (Ross, n.d.; cf. Cottingham, 16). “[H]e wanted to define an area in which everything could be completely explained by a reductionist, mechanistic physical science” (Ree, p. 91). “[T]he brand of knowledge Descartes seeks requires, at least, unshakably certain conviction,” and such knowledge he considered to be unavailable from authority or sense-perception (Newman, 2005). “Arithmetic, Geometry, and the other sciences of the same class, which regard merely the simplest and most general objects…contain somewhat that is certain and indubitable” (Descartes, 1952b, 31:77). Descartes challenged scholasticism generally because he thought that it had been convoluted by “jargon-manipulation and the juggling of authorities” as “the paramount road to academic advancement” (Cottingham, p. 5). [NOTE: The purpose of this article is not to assess scholasticism or Aristotelianism.]

Banach summarizes Descartes’ starting position: “In order to show that science rested on firm foundations and that these foundations lay in the mind and not the senses, Descartes began by bringing into doubt all the beliefs that come to us from the senses…. The obvious implication is that, since we do know that external objects exist, this knowledge cannot come to us through the senses, but through the mind” (n.d., parenthetical item in orig.). Maritain observed: “Descartes, on the contrary, who with the rest of the moderns makes science consist in invention rather than in judgment, has a hankering for a Science which with one and the same movement proves by discovering, and discovers by proving, established in complete certitude from its inception, rejecting of itself as an attempt against its being, every purely probable element” (1944, p. 55).

His method of acquiring this scientific conviction begins with doubt, which for Descartes took root in his general objection to his instructor’s methods (2007, p. 17). “[W]hen I considered the number of conflicting opinions touching a single matter that may be upheld by learned men, while there can be but one true, I reckoned as well-nigh false all that was only probable” (2007, p. 15). His doubt leads Descartes to the “insistence that philosophy should begin with the self and travel outward” (Durant, 1926, 336).

Whatever Descartes’ specific theological positions, his philosophical starting-point is dangerous to faith. Descartes’ project began by trusting in reason to the exclusion of revelation (both natural and special). This procedure is in contrast with Paul’s prescription: “For since the creation of the world His invisible attributes are clearly seen, being understood by the things that are made, even his eternal power and Godhead, so that they are without excuse” (Romans 1:20). It falls to the Christian apologist to reason properly about what God has revealed (see Warren, 1982), and to defend the faith against the attacks of doubt. God expects us to use our senses as we come to a knowledge of Him (1 John 1:1-3), so we must critically analyze any approach to knowledge that attempts an overthrow of empiricism. As Wilson noted, Descartes had “a general metaphysical vision of reality, and commitments to a special conception of what the world is like and how it works” (1978, p. 221). We must ask whether that metaphysical vision is consistent with Christianity.


From the foregoing, it is obvious that Descartes became a rationalist. Generally speaking, a rationalist “accepts the supremacy of reason, and aims at establishing a system of philosophy and ethics independent of arbitrary assumptions and authority” (“FAQs,” n.d.). Descartes summarized his rationalist perspective: “[I]t is now manifest to me that bodies themselves are not properly perceived by the senses nor by the faculty of imagination, but by the intellect alone” (2007, p. 88). Descartes sought “an absolute foundation for knowledge by proposing to doubt all things and accept as knowledge (or at least as a foundation for knowledge) only what could not be doubted” (Cannon, 2001, parenthetical item in orig.). For Descartes, this narrowed the field of possible knowledge, leaving only that of which “the light of reason” or “the light of nature” provide assurance (see Markie, 1992, p. 147; cf. Maritain, 1944, pp. 50, 115):

I thought that a procedure exactly the opposite was called for, and that I ought to reject as absolutely false all opinions in regard to which I could suppose the least ground for doubt, in order to ascertain whether after that there remained aught in my belief that was wholly indubitable. Accordingly, seeing that our senses sometimes deceive us, I was willing to suppose that there existed nothing really such as they presented to us; and because some men err in reasoning, and fall into paralogisms (pieces of false reasoning)…I, convinced that I was open to error as any other, rejected as false all the reasonings I had hitherto taken for demonstrations (2007, p. 31, parenthetical item added).

Descartes had been troubled by the recognition that his senses deceived him on occasion. For example, “I considered that the very same thoughts (presentations) which we experience when awake may also be experienced when we are asleep, while there is at that time not one of them true” (2007, p. 31, parenthetical item in orig.; cf. pp. 76-77; cf. Wilson, 1978, pp. 17ff.). Furthermore, “Descartes cannot yet be certain if there are any bodies in existence. Since one cannot ‘sense’ unless there is body present (otherwise it is a dream or a hallucination or a mirage or an illusion)” (Mahon, n.d., parenthetical item in orig.). In examining why his senses deceived him, Descartes proposed the possibility of a deceptive demon. “[S]ome malignant demon, who is at once exceedingly potent and deceitful, has employed all his artifice to deceive me; I will suppose that the sky, the air, the earth, colors, figures, sounds, and all external things, are nothing better than the illusions of dreams, by which this being has laid snares for my credulity” (2007, pp. 78-79).

Descartes had disregarded empirical knowledge entirely (see 2007, p. 79), and settled on the one reality that, he believed, satisfied his radical criterion for truth:

But immediately upon this I observed that, whilst I thus wished to think that all was false, it was absolutely necessary that I, who thus thought, should be somewhat; and as I observed that this truth, I think, therefore I am (COGITO ERGO SUM), was so certain and of such evidence that no ground of doubt, however extravagant, could be alleged by the skeptics capable of shaking it, I concluded that I might, without scruple, accept it as the first principle of the philosophy of which I was in search (p. 31, parenthetical item and emp. in orig.).

Descartes focused on the one thing he believed is certain: that he is a “thinking thing” (2007, p. 84). He explained his rationale further in his Principles: “[W]hile rejecting in this way all those things which we can somehow doubt, and even imagining them to be false, we can indeed easily suppose that there is no God, no heaven, no material bodies; and even that we ourselves have no hands, or feet, in short, no body; yet we do not on that account suppose that we, who are thinking such things, are nothing” (p. 5). Cottingham observed: “The most striking feature about the accounts Descartes himself gives of the Cogito argument is that the certainty involved stems from the fact that the mediator has pushed his doubt to the limit…. [T]he very fact that I am around to entertain the doubt shows that I must exist” (p. 38).

Next, Descartes needed to develop a “permanent system of knowledge” from his theory of doubt (see Cottingham, p. 42). Wilson explained: “The upshot of the argument of the Meditations is that an external physical world can be proved to exist, thus in a sense affirming what everyone ‘knew’ all along; but the proof turns out to be arduous and to require immaterialist premises: people are wrong in thinking the direct evidence of the senses is sufficient” (p. 45). In this process of rebuilding the knowledge he previously deconstructed via radical doubt, Descartes reintroduced God. This move was essential to Descartes’ conviction that material objects exist:

Is there not a God…who causes these thoughts to arise in my mind? But why suppose such a being, for it may be I myself am capable of producing them? … And in truth, as I have no ground for believing that Deity is deceitful, and as, indeed, I have not even considered the reasons by which the existence of a Deity of any kind is established, the ground of doubt that rests only on this supposition is very slight, and, so to speak, metaphysical (2007, pp. 81,90).

Descartes insisted that of all his perceptions of external objects, including his own body, the notion of God “has certainly in it more objective reality than those ideas by which finite substances are represented,” and that the effects of his perceptions must have correlative causes (2007, pp. 92-93). “And how could the cause communicate to it this reality unless it possessed it in itself? And hence it follows…that the more perfect, in other words, that which contains in itself more reality, cannot be the effect of the less perfect” (p. 93). Since Descartes clearly had an idea of God in his consciousness, and since he believed himself incapable of originating this idea independent of some exterior force on his intellect, then he concluded that that Being caused the idea (see pp. 94-97).

I should not, however, have the idea of an infinite substance, seeing I am a finite being, unless it were given me by some substance in reality infinite…. The idea, I say, of a being supremely perfect, and infinite, is in the highest degree true; for although, perhaps, we may imagine that such a being does not exist, we cannot, nevertheless, suppose that his idea represents nothing real, as I have already said of the idea of cold. It is likewise clear and distinct in the highest degree, since whatever the mind clearly and distinctly conceives as real or true, and as implying any perfection, is contained entire in this idea (pp. 96,97).

Hence Descartes did away with the demon, concluding that it is impossible for God, being perfect, to deceive him (p. 103). “[H]e is no deceiver…” (p. 115).

Having reached a conviction that God is real, Descartes proceeded to claim partial knowledge of material objects by virtue of God’s grace:

I cannot deny that we may have produced many other objects, or at least that he is able to produce them, so that I may occupy a place in the relation of a part to the great whole of his creatures…. And although there are perhaps innumerable objects in the world of which I have no idea in my understanding, it cannot, on that account be said that I am deprived of those ideas as of something that is due to my nature, but simply that I do not possess them, because, in truth, there is no ground to prove that Deity ought to have endowed me with a larger faculty of cognition than he has actually bestowed upon me (p. 105; cf. pp.112-113).

On Descartes’ account, humans can be certain that they possess knowledge only because God exists and can be trusted not to deceive.


Consider three problems with Descartes’ approach to knowledge: First, “Insistence upon a standard of absolute certainty eliminates the middle ground of reasonable evidence. It suggests that if you don’t have complete certainty you have no evidence at all” (Cannon, 2001). Anthony Kenny summarizes this objection: “Few would quarrel with the starting point: it is true that we grow up uncritically accepting many beliefs which may be false. But is it necessary, in order to rectify this, that we should on some occasion call in question all our beliefs? Can we not correct them piecemeal?” (p. 18). If, for example, when I strike my fist against a wall, I have an insufficient level of certainty that the wall is real, then what level of certainty is needed? Human beings necessarily operate on a level of faith in their senses, but that faith is biblical (as we will see), and certainly sufficient for human existence.

Kant points out that the Cogito falls short of proving Descartes’ point, because it also is an empirical notion: “The ‘I think’ is…an empirical proposition, and contains the expression, ‘I exist.’ But I cannot say ‘Everything, which thinks, exists;’ for in this case the property of thought would constitute all beings possessing it, necessary beings. Hence my existence cannot be considered as an inference from the proposition ‘I think,’ as Descartes maintained” (2003, p. 225). Also, Kenny raises the question of identity: “Is not Descartes rash in christening the substance in which the doubts of the Meditations inhere ‘ego’? To be sure, he explains that he is not yet committing himself to any doctrine about the nature of the ego…. But what ‘I’ refers to must at least be distinct from what ‘you’ refers to; otherwise the argument might as well run ‘cogitatur, ergo es’ (“thought exists, therefore, you are”) as ‘cogito ergo sum’ (“I think, therefore I am)” (1968, p. 62, parenthetical items added).

Second, “Insistence upon absolute clarity and distinctness to the skeptical reflecting mind eliminates consideration of any respect in which reality transcends full and determinate representation” (Cannon). Indeed, the very fact that Descartes knew that his senses occasionally “deceived” him, demonstrates that his senses usually (typically) provided him with accurate perceptions. The Bible teaches that we generally can place confidence in our senses, even to the degree of sinning, recognizing the need for salvation, and accessing remission of sins (e.g., Genesis 13:15; Matthew 5:13; Acts 13:44; John 20:24-30; etc.). Descartes’ argument is intelligible only if the illusive nature of dreams, for example, does not inhibit our general understanding of reality. Kant, therefore, emphasizes the need for “sensuous phenomena” in the “empirical world” while recognizing its limitations—even if they are God-given (2003, pp. 42,43,316; 1952, 42:337). In the Fourth Meditation, Descartes would seem to agree: “I have no reason…to think that it was obligatory on [God] to give to each of his works all the perfections he is able to bestow upon some” (2007, p. 105).

In this context, it is remarkable that Descartes moves swiftly from doubting his senses, to relying on them (and problematically placing the seat of empirical knowledge in the pineal gland; see Lockhorst, 2008; cf. Kenny, pp. 225-226):

And as I observed that in the words “I think, therefore I am,” there is nothing at all which gives me assurance of their truth beyond this, that I see very clearly that in order to think it is necessary to exist, I concluded that I might take, as a general rule, the principle, that all things which we very clearly and distinctly conceive are true, only observing, however, that there is some difficulty in rightly determining the objects which we distinctly conceive (2007, p. 32).

Perhaps this occurs because Descartes did not wish to be separated from the reality he knew prior to settling on the Cogito: “Proposing to rebuild one’s knowledge from the ground up because a number of things that once seemed true have become doubtful or false, as Descartes does, is a lot like being in a boat out on the ocean and proposing to abandon ship in order to rebuild the boat from the keel up just because it has developed a few leaks” (Cannon).

Third, Descartes did not provide a convincing reason for his rejection of the possibility that a demon was placing false ideas in his consciousness. Because all of Descartes’ evidence was rational, and none of it was empirical, his basis for thinking that God exists was a “clear and distinct” idea of a Person, “infinite, eternal, immutable, independent, all-knowing, all-powerful” (2007, pp. 96,97). Why could that idea not have been placed in Descartes’ mind by a god who is actually deceitful? Descartes finished where he started, but not prior to attempting an overthrow of empiricism. His pre-existing belief in God rescued Descartes from his own personal skepticism; but what of those readers who find his argument for the existence of God unconvincing? The truth is that God appeals to us by presenting us with biblical and extra-biblical evidence that agrees with our observation and rationality, all of which ultimately are derived from Him (Jeremiah 51:15).


Descartes’ radical doubt, which would entail dispensing with all epistemological knowledge, also would place an insurmountable roadblock to biblical faith. However, his doubt has been shown to be invalid. It is telling that rationalists still maintain a certain scientific epistemology (“FAQs,” n.d.). Perhaps we can hypothesize, with Maritain, that pride ultimately led Descartes to his radical doubt (pp. 33-62):

The pride of human knowledge appears thus as the very substance, solid and resistant, of rationalist hopes. Pride, a dense pride without frivolity or distraction, as stable as virtue, as vast a geometric extension, bitter and restless as the ocean, takes possession of Descartes to such an extent that it would seem the universal form of his interior workings and the principle of all his suffering (p. 56).

This is a stark contrast to Christ’s portrait of those who are pleasing to Him: “Whoever humbles himself as this little child is the greatest in the kingdom of heaven” (Matthew 18:15).

In light of Descartes’ major contributions to modern science and mathematics, it is remarkable that his doubt also led him to a radical distinction between mind and body, which we will not detail or critique here (it has been done elsewhere: see Hatfield, 1992, pp. 335-370; Kenny, 1968, pp. 216-226; Wilson, 1978, pp. 50-99). Ree summarized the necessity for this dualism: “[H]is dualism of mental and physical properties implied that since human beings had minds, they were more than mere parts of an all-engulfing physical universe” (p. 100). The connection between Descartes’ epistemology and his physiology, in light of the biblical doctrine of mind and body, would be the next logical step in this inquiry. [NOTE: Special thanks to Michael R. Young, Ph.D., for help with research.]


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