The institutional and intellectual authority of the Roman Catholic Church had been swept away in a number of countries as the result of the activities of such reformers as Martin Luther and John Calvin. Even in countries that remained Catholic, such as Descartes's France, the Church was on the defensive and was wary of unorthodox thought. Descartes wished to avoid any appearance of deviation from Catholic doctrine. Upon hearing of the conviction of Galileo by the Inquisition, he suppressed the publication of his early book Le Monde (The World), in which he had endorsed the thesis that the earth moves. (The book was published posthumously.) He also had the manuscript of the Meditations on First Philosophy circulated to several theologians before its publication, and he added their objections (as well as the objections of various philosophers) with his responses to the published edition of the Meditations. The Principles of Philosophy ended with this article.
207. Nevertheless all my opinions are submitted to the authority of the Church. At the same time, recalling my insignificance, I affirm nothing, but submit all these things to the authority of the Catholic Church, and to the judgment of those wiser than myself; and I wish no one to believe anything I have written, unless he is personally persuaded by the force and evidence of reason.
The Meditations (1641) was dedicated to the Faculty of Sacred Theology of Paris, and in dedication letter, Descartes asserted that "I have always thought that two issues--namely, God and the soul--are chief among those that ought to be demonstrated with the aid of philosophy rather than theology" (cf. the Author's Preface to the Discourse on Method). The sub-title of the work is "In which the Existence of God and the Distinction between the Soul and the Body Are Demonstrated." As will be seen in the course of these notes, Descartes sought to demonstrate God's existence not only to persuade the unbeliever (as he professes in the "Dedication"), but also to support his belief in the existence of the physical world as well as his beliefs about mathematics. In his later work Principles of Philosophy, Descartes even undertook to derive laws of physical nature from the nature of God.
In the Discourse on Method, Descartes expressly declared that he would not try to use his frail reasoning in support of "revealed truths," since explaining them would require "some extraordinarly assistance from heaven" (Part I). Nonetheless, Descartes could not refrain from trying to use his reason-based philosophy to tackle theological issues. The most notable case is that of transubstantiation, the change in substance from bread to the body of Christ and from wine to the blood of Christ (Fourth Set of Replies to the Meditations, "To Points which May Cause Difficulty to Theologians").
As Descartes explained in the "Letter to Father Dinet" published in response to Father Bourdin's objections to the Meditations, he took his philosophy to be able to explain theological truths better than "the commonly accepted philosophy" (i.e., that based on Aristotle). Further, given that his own philosophy is true, it cannot be in conflict with theological truths, since "one truth can never be in conflict with another." Descartes's foray into theology had real consequences. He had given a physical explanation of transubstantiation in a letter to Father Masland, who soon after was dispatched to the Americas as a missionary.
Theses about God play a central role in the "modern" philosophy of Descartes as they do in the philosophy of any of the Medievals. Some have argued that Descartes was insincere in integrating "natural religion" into his natural philosophy and submitting to the authority of the Catholic Church, but this question cannot be pursued here. Despite all the protestations, Descartes's works (as were those of nearly all the other philosophers we will study) were put on the Index of Forbidden Books in 1663. The author of the 1908 Catholic Encycolpedia, while acknowledging Descartes's genius and influence, thought that his quantitative account of the world was outmoded and soon would be replaced.
The sixteenth century had seen an explosion of interest in the natural world. The great voyages of discovery were undertaken, vastly widening people's view of the world. Copernicus had revived and argued persuasively for the heliocentric theory of the solar system. Kepler had established this system on a firm mathematical footing. Moreover, many scientific and metaphysical writings from ancient times had been re-discovered, providing a powerful stimulus for innovative thinking.
The seminal figure in the early stages of the Scientific Revolution was the Italian philosopher-scientist Galileo Galilei. He made numerous discoveries using telescopes he invented, and he used his observations to challenge directly the Aristotelian view that the heavens are perfect and immutable. He argued persuasively for the Copernican thesis of the motion of the earth relative to the sun, which Catholic theologians believed to be inconsistent with Biblical teachings. And he extensively applied mathematical techniques to the study of motion. Although a rear-guard action was fought against his advances, his ideas were unstoppable.
Descartes was thirty-two years younger than Galileo and shared many of the same interests, and more. Along with the Discourse on Method, he published in 1637 books on analytical geometry (which he invented), optics, and meteorology. His Principles of Philosophy (1644-47) attempted no less than an account of the physical world, from which "no phenomena of nature have been omitted" (Part Four, Article 199). Although many of Descartes's results have been discredited, he was the first to state a principle of inertia that would become central to Newton's physics (Part Two, Article 37).
The Meditations contains the metaphysical underpinnings of Descartes's natural philosophy. (Most of the main results are recapitulated in the Principles of Philosophy.) He wrote in a letter to Mersenne in 1641,
. . . I may tell you between ourselves that these six Meditations contain all the foundations of my Physics. But please do not tell people, for it might make it harder for supporters of Aristotle to approve them. I hope that readers will gradually get used to my principles, and recognize their truth, before they notice they destroy those of Aristotle. (ATIn particular, Descartes tried to establish that the real attributes of bodies are extension, figure, motion or rest, duration, and number. All of these attributes are mathematically quantifiable. So if he could establish the credientials of mathematics, he would be able to claim knowledge about the fundamental characteristics of the physical world. This is one of the most important consequences of that seminal work.
Aristotle's philosophy leaves little room for the application of mathematics to the physical world, and so one can see that there was a need for showing that the real attributes of objects are subject to mathematical treatment. But it might be thought odd that the credentials of mathematics need be established at all. Descartes's desire to defend knowledge of pure mathematics stems from his more general goal of defeating skepticism, which had become a major intellectual force in the sixteenth century. It posed a threat not only to religion, but to the nascent sciences as well.
Descartes tried to fight fire with fire. His "method of doubt" was to apply the strongest skeptical arguments against his beliefs and then to show that some of his beliefs remain certain in the face of those arguments. It is an irony of history that it is the skeptical arguments, rather than Descartes's arguments for certainty, that are most discussed today. Whether or not we find the anti-skeptical project to be successful, Descartes himself thought that he had given "Arguments by which I, first of all men, upset the doubt of the Sceptics" (Seventh Objections to the Meditations , "Third Question" AT VII 550).
Descartes assumes an autobiographical style not often seen in philosophical treatises (an exception being Augustine's Confessions). In both the Discourse on Method and the Meditations on First Philosophy, he describes an intellectual journey from the unstable opinions he had formed from his early experiences and education to indubitable metaphysical and scientific knowledge. His system was eventually laid out in the Principles of Philosophy, which he had hoped would be used as a textbook in the universities. The Meditations, which will be the main focus of these lectures, embodies both a description of the journey and a sketch of the resulting system.
Before turning to the Meditations, we will take a brief look at a portion of Descartes's Discourse on Method, which accompanied his treatises on optics, meteorology, and geometry. The theme of the first section is his search for a proper method of arriving at knowledge. Descartes describes coming to the realization that while what he learned from books in school was often useful, it is unenlightening, at least in the case of philosophy. All that is found is disputes with no resolution. He then turned to travel, studying "the great book of the world." Again, he found much disagreement, especially due to differences in customs. Ultimately, he turned to himself, where he discovered that he could arrive at knowledge and purge himself of false opinion by reasoning in a way similar to the way in which geometers reason.
The Discourse is presented as a sampler of material that was presented more fully in the Meditations, though it contains some material not found in his later book (for example, the argument for the claim that non-human animals are automata). Descartes intended the Discourse to be read by a popular audience, writing it in French. The Meditations, on the other hand, were aimed at the community of scholars and were written in Latin. In the Discourse, Descartes appealed to the public for objections, while he solicited objections to the Meditations from a hand-picked set of scholars. He noted in its Preface that the Discourse was "designed to be read indiscriminately by everyone, let weaker minds be in a position to think that they too ought to set out on this path."
The Meditations describes an intellectual journey of a thinker who begins with naïve opinions and ends with certain knowledge. The transition from opinion to knowledge requires a massive intellectual upheaval, according to Descartes. If he has a false opinion, it might be appealed to in support of some other opinion, and this can be a source of error. So it would be best for him to get rid of all his false opinions. But at the outset, he does not have any way of determining which of his opinions are false. His only recourse is to treat any opinion that he had some reason to think might be false as if it were actually false. In this way, he would be do the best he could to empty his mind of all false opinions.
Of course, he might well empty his mind of some true opinions by this method. If so, he could come to have knowledge of their truth once he learned to recognize the difference between what is true true and false. To illustrate this method, Descartes resorted to a "homely" example of someone trying to avoid another kind of contamination.
Supposing he had a basket of apples and fearing that some of them were rotten, wanted to take those out lest they might make the rest go wrong, how could he do that? Would he not first turn the whole of the apples out of the basket and look them over one by one, and then having selected those which he saw not to be rotten, place them again in the basket and leave out the others? (Reply to seventh set of objections to the Meditations AT VII 481).This analogy does not work perfectly, though. Descartes never tries to set aside all of his opinions. He instead progressively casts doubt on various groups of opinions which are based on some preconceived notions that he had had. If he were indeed to set aside every opinion he had, he would have nothing left on which to base the rest of the investigation.
After having taken as false as many of his opinions as are subject to the slightest rational doubt, Descartes could feel secure with those that he could not rationally doubt. His basic strategy was to try to discover in his indubitable beliefs a mark of their truth, and then use that mark to recover some of the provisionally-discarded opinions. In practice, it turns out to be harder to dispel the grounds for doubting some opinions than the grounds for doubting others.
A constant theme in Descartes is a distrust of the evidence that we take to be produced by the bodily senses (sight, touch, taste, smell, hearing). Skeptics had always pointed to the conflicts between the sensible appearances of things. For example, a tower seems round from a distance and square close-up. The fact of perceptual variation provides some reason to doubt any opinion about the specific characteristics of material things formed on the basis of the way they appear in sense-perception.
It might be thought that the doubt induced by perceptual variation is limited to objects with respect to which he is not in an optimal position: they are too small or too far away. Opinions such as that he is sitting by the fire in his dressing gown seem to be beyond doubt, at least given that he is not mad.
But one does not have to be mad to doubt what seems most obviously true about material objects. Descartes notes that in his dreams he has often been quite convinced that he was sitting by the fire in his dressing gown when he was in fact lying naked in bed. Moreover, he lacks any apparent means for determining whether he is dreaming or awake, so there is reason to doubt even the most obvious of his perceptually-based opinions about what is going on in the material world.
At this point, Descartes for the sake of argument supposes that he is dreaming and has no body at all. Even if this were so, the images of his dreams would have to come from something. And if that something were not composite like his body, it would at least have to be something "even more simple and general." First, there is "corporeal nature in general," along with its extension. Second, there are the characteristics of corporeal things, such as their quantity, size, number, place and time. In the Second Meditation, Descartes will argue that these are the fundamental attributes of bodies.
He suggests that his opinions about these simple and general matters are not subject to rational doubt, because they are true whether he is asleep or awake. His examples are that two and three equal five, and that a square has at most four sides. "It does not seem possible that such obvious truths should be subject to the suspicion of being false" (Meditation One).
At this point, Descartes raises the strongest skeptical objection of all. It is based on a long-held opinion that he was created by a God who is powerful enough to do anything. If that opinion is true, it seems that God could have created no corporeal nature at all, yet made him in such a way that what appears to him looks just like a corporeal world. So now he has reason to doubt that a corporeal world exists.
When thinking about this God, Descartes comes to an even more fundamental doubt. He has the opinion that other people have made errors in matters about which they think they know most perfectly. He asks rhetorically whether God could have made him so as to be deceived all the time about such simple matters as whether two and three make five. And on the supposition that he came from some lesser cause than God, the possibility of his being "so imperfect that I am always deceived" is even stronger. His conclusion is stark:
Eventually I am forced to admit that there is nothing among the things I once believed to be true which it is not permissible to doubt -- and not out of frivolity or lack of forethought, but for valid and considered arguments. Thus I must be no less careful to withhold assent henceforth even from these beliefs than I would from those that are patently false, if I wish to find anything certain. (First Meditation)One of the main questions in Descartes scholarship is whether Descartes had dug a hole so deep that he could not climb out.
Descartes is famous for having introduced "an evil genius, supremely powerful and clever, who has directed every effort at deceiving me" (Meditation One). It is easy to think that the evil genius would be capable of deceiving us in the way just described, i.e., by having made us to be radically imperfect. But in fact, the genius would be fooling us only in the first way described, merely by making everything appear the way it would were there a corporeal world.
Because of this limitation, the scope of "demon doubt" is limited to his opinion about the existence of the material world. Descartes makes the supposition of an evil genius because his opinion that such a world does exist would otherwise remain highly probable. He is intent on conceiving his old opinions as "wholly false and imaginary," for reasons that become clear only in the Second and Sixth Meditations, where Descartes argues for the separate existence of body and mind. Contemporary theorists of knowledge tend to regard the existence of the evil genius as a doubt that must be cleared away before we can know that material things exist, rather than as a mere supposition.
No Doubts About My Own Existence
Despite his claim to having brought all his beliefs into doubt, Descartes has not quite done so. For he must have had the opinion that he exists, at least when he is considering whether he exists. And this is something for which he can have no rational grounds for doubt. As Augustine had pointed out more than a millenium earlier, the attempt to doubt one's own existence is futile (On the Trinity, 14, Soliloquies, Book II, Chapter 1, The City of God, Book XI, Chapter 26). An evil genius doing his best at deception "will never bring it about that I am nothing so long as I shall think that I am something." Thus one existential opinion is found to be immune from doubt and is the "item of knowledge that I claim to be the most certain and evident of all" (Meditation Two). This existential claim is known by the Latin word "Cogito," which means "I think." Most philosophers acknowledge that Augustine and Descartes were correct that we are certain that we exist when trying to doubt that we do.
Having discovered that he is certain that he exists (when thinking about whether he exists), Descartes goes on to ask what he is. Suppose he were to answer by saying that he is a human being. Then he would have to give an account of what a human being is. The Aristotelian doctrine that the human being is that humans are rational animals. Descartes rejects this account, not because of any material shortcomings it might have, but because it is a conceptual definition, whose components "rational" and "animal" themselves would need to be defined, with no end in sight. Instead of pursuing definitions, Descartes turns to opinions about what he is that had previously occurred to him spontaneously and naturally. The key opinion is that he had a body, which operates in various ways. Descartes sets up his eventual separation of mind and body by noting that he never did understand how a body could move itself, sense, and think. (Aristotle had attributed the source of these activities to the soul.)
The real problem, though, is not one of explanation of how he could be a body. Rather, it is the fact that he has supposed that he has no body at all. Specifically, he has supposed that there is an evil genius, "who deliberately tries to fool me in any way he can." Citing the principle that, "Certainly, in the strict sense, the knowledge of the existence of this 'I' is not dependent upon things whose existence I do not yet know" (Meditation II), he concludes that his imagination cannot, by referring to a body, provide him with knowledge of what he is. The best strategy is to withdraw his mind from considerations of the imagination "so that it can perceive its nature as distinctly as possible." Here, we have a fore-shadowing of two later claims: that the mind has a nature or essence, and that the key to understanding a nature is the distinctness of one's perception of that nature.
Now we finally get to the nature of the "I." It is "A thing that thinks" (res cogitans). The thinking that characterizes the mind is broken down into a number of functions. The first group of functions is based on the carrying out of the activity of doubt. (Compare Augustine, On the Trinity, 14, on this point.).
The other two functions are not required for the purposes of systematic doubt. They are imagining and sensing (even against one's will). Imagining is the formation of mental images. Sensing is noticing "many things that appear to come from the senses." Both of these activities can occur whether or not one has a body (or so Descartes claims). As for sensing, this would involve seeming to see, to feel, to hear, etc., which can take place even in a dream.
Descartes concludes the Second Meditation with a discussion of his beliefs about bodies, giving free rein to his imagination (as opposed to his understanding) for the time being. His main point is to establish the claim that the mind is better known than any body. We will not treat this argument here, except to note that it is not very persuasive. What is of real interest is Descartes's separation of the characteristics of bodies into two types: those that are grasped by the understanding and those that are mere products of sense and imagination. The former are attributed to the nature of body (which does not require that any bodies exist) while the latter are not.
As an example, Descartes uses a piece of wax that is freshly drawn from a bee-hive. When placed by a fire, its various characteristics gradually change until the resulting puddle does not resemble the original at all. All the characteristics that appear to come from the senses, the color, fragrance, hardness, etc. have been completely transformed. What is left is only three characteristics, that the wax is:
In the Third Meditation, Descartes picks up the main thread once again. He has established beyond rational doubt that he exists, but he has not yet established the existence of anything other than himself. To do this, he must banish the grounds for doubt laid down in the First Meditation. The best way to do this would be to discover a criterion by which to distinguish what is subject to doubt and what is not subject to doubt. To do so, he examines the "first instance of kowledge," which is the certainty that he is a thinking thing. All that he can find in it, with respect to its truth, is a very clear and very distinct perception of his being a thinking thing. "Yet this would hardly be enough to render me certain of the truth of a thing, if it could ever happen that something that I perceived so clearly and distinctly were false" (Third Meditation). From this he adopts a general rule or criterion that whatever is perceived very clearly and very distinctly is true.
With this criterion in hand, Descartes notes that his previous opinions (about the existence of bodies, for example) were not being based on clear and distinct perception. His judgment about these things, even if true, "was not the result of the force of my perception." If his opinions were true, it was only by accident. Descartes will not discover until the Sixth and final Meditation the requisite clear and distinct perceptions needed to give him certainty about the existence of bodies.
On the other hand, he finds now that there are some judgments which can be made based on the force of his perception: judgments about very simple and easy things like five being the sum of two and three. Here is what Descartes says about these matters:Whenever I turn my attention to those very things that I think I perceive with great clarity, I am so completely persuaded by them that I spontaneously blurt out these words: "let him who can deceive me; so long as I think that I am something, he will ever bring it about that I am nothing. . . . Nor will he even bring it about that perhaps two plus three might equal more or less than five, or similar terms in which I recognize an obvious contradiction." (Third Meditation)So Descartes is compelled to believe in cases of clear and distinct perception. He refuses to allow that he can be deceived in these matters. Yet he concedes that he has not yet shown that there is no God who has given him a nature that would "cause me to err even in those matters that I think I intuit as clearly as possible." To remove this "very tenuous, and, so to speak, metaphysical" doubt, he must establish that God exists and is no deceiver, which is his next task. He states that, "if I am ignorant of this, it appears I am never capable of being completely certain of anything else."
It is crucial to see why it is that God's existence must be proved before Descartes can attain "complete" certainty. At the time he is attending to his clear and distinct perceptions, Descartes refuses to allow any possibility of deception. But at other times, and in particular when he is thinking about the possibility of his being defective, rational doubt can creep back into his mind.
This point comes out most clearly in the Replies to the Second Set of Objections. Consider an atheist who can have a clear awareness that the sum of the angles of a triangle are equal to two right angles. This clear awareness is not knowledge, because it can be rendered doubtful if the atheist reflects on the possibility that he could be deceived in such matters. Only knowledge that God exists can rule out this possibility. This implies that all that Descartes has established at this point in the Third Meditation is that he is certain at the time of his perception of the truth of what he clearly and distinctly perceives.
The proof for God's existence will depend on the question of where our ideas (i.e., that which we perceive) come from. Before undertaking the proof, Descartes classifies ideas according to their apparent origin and indicates what they are supposed to be about.
The rational grounds he does have for thinking that we have adventitious ideas resembling bodies, that they are produced against his will, are inadequate. But for all Descartes knows, they may have an unknown source in himself, as in the case of dreams. If they are self-produced, they might resemble nothing at all.
Even if the ideas are adventitious, it is not certain that they resemble their causes. Suppose the sun produces by "sense" an idea of it in my mind. If the sun resembles this idea, then it is a very small body. But rational inquiry yields a quite different idea of the sun, according to which it is a very large body. So it turns out that it is more reasonable to think that an adventitious idea of the sun does not resemble its cause than to think that it does. And once again, Descartes is pushing the fundamental theme that objects are better known through the understanding than they could be by sense--the thesis of "rationalism."
Descartes wants to know whether God exists, so the question is whether the idea he has of God resembles an existing thing or not. The short answer to this question is that the idea could not exist if it had not been produced by a being resembling it. The idea of God is an idea of an infinite being, and it would require an infinite being to produce such an idea. The reason is that the cause of an idea must have at least as much reality as its effect.
We will not go into the details of this argument. It relies heavily on conceptions more ancient or medieval than modern. But a key aspect of the proof is that its premises are sanctioned by the "light of nature." This is no more than to say that they are very clearly and distinctly perceived. The light of nature must be strictly distinguished from those teachings of nature which are merely spontaneous opinions, such as the opinion that our ideas resemble their causes.
In the remainder of the Third Meditation, Descartes seeks to establish that God is his creator, as well as the creator of the idea of God he has. If so, then the idea of God would seem to be innate in his soul, like a signature of an artist on a canvas. A final conclusion is that God is no deceiver. This is because his idea of God is that of a perfect being, and God must be perfect for him to have that idea. A perfect being has no defect and so would, by its nature, never deceive, "for it is manifest by the light of nature that all fraud and deception defend on some defect."
The claim that God made him and is no deceiver gives rise to an obvious question for Descartes: why is he deceived at all. The answer is that "since [God] did not wish to deceive me, he assuredly has not given me the sort of faculty with which I could ever make a mistake, when I use it properly" (Fourth Meditation). The key phrase here, of course, is "when I use it properly." We will shortly have an account of the proper use of our faculty of judgment, but in the meantime Descartes must recognize that God could have made him in such a way that he could never make a mistake whenever he used his faculty of judgment at all. This gives rise to a problem. "No doubt God could have created me such that I never erred. No doubt, again, God always wills what is best. Is it then better that I should be in error rather than not?"
The problem of error raised here is directly parallel to the long-standing problem of evil. Why is it best that God created a world in which evil exists? Descartes's answers to the problem are very much the same as those given to the problem of evil. We don't know why God does what God does, and we must view the perfection of the world in terms of the world as a whole and not in terms of the parts. Ultimately, in the Sixth Meditation, Descartes will conclude that he is made well-enough.
The rest of the answer depends on the claim that he is never deceived if he uses his faculty of judgment properly. This is so because he is free not to believe, in those cases where his perception falls short of clarity and distinctness. He is made so that his will is indifferent regarding what to believe. It can be pulled one way or another by appearances. It is his God-given duty to restrain his will when it becomes improperly inclined toward assent. On the positive side, Descartes can now explain his compulsion to believe in cases where he does perceive very clearly and distinctly: "not that I was coereced into making this judgment because of some external force, but because a great light in my intellect gave way to a great inclination in my will" (Fourth Meditation). On Descartes's view, the more that one is inclined toward judgment due to one's undertanding of a thing, the more free one is in judging. So one judges most freely when one does so on the basis of clear and distinct preception.
In the "Synopsis" of the Meditations, Descartes asserted that the "requirement that we know that everything that we clearly and distinctly understand is true, in exactly the manner in which we understand it, . . . could not have been proven prior to the Fourth Meditation." The contribution of the Fourth Meditation is to provide an explanation of the nature of error. Descartes claims that God could not have given him a faculty of judgment which would lead him into error if used properly. The proper use of the faculty of judgment in metaphysics is to assent only on the basis of clear and distinct perception. Since these perceptions are created by a God who is no deceiver, they must be true.
The beginning of the Fifth Meditation concerns the nature of bodies, whose existence is to be proved in the Sixth, and final, Meditation. The key characteristic of bodies is their extension in length, breadth and depth. We know that the nature of bodies is to be extended, whether they exist or not. So clear is this, that "it seems I am not so much learning something new as recalling something I knew beforehand." The quantiative attributes of a thing (such as a triangle) are not of my own making, but express the "determinate nature, essence, or form, which is unchangeable and eternal." Here Descartes adopts a Platonistic account both of the attributes of bodies and of our knowledge of those attributes. He rejects what is now called "concept empiricism," according to which our idea of a triangle, for example, is derived from empirical observation of corporeal triangles. The reason for this rejection is that we can think of all kinds of geometrical shapes which have never been experienced. (The empiricist would reply that such ideas can be fabricated by the imagination from what has been experienced, such as lines.)
The Ontological Proof of God's Existence
The appeal to eternal natures allows Descartes to give a second argument for the existence of God. This is a version of the "ontological argument" first raised by Anselm of Canterbury in the 11th century. Here is a reconstruction of that argument.
The original argument of Anselm had been criticized by Thomas Aquinas on the grounds that even though one cannot think of God as not existing, this does not establish that God must exist. Descartes's linkage of natures with clear and distinct perception was perhaps intended to undercut Thomas's objection.
A later objection, due to Kant, attacks the third step. According to Kant, existence is not something that can pertain to the nature of any thing. The only thing that belongs to a nature is a set of properties, but existence is not a real property of things. Arthur Schopenauer has pointed out that such a principle was enunciated by Aristotle: "To be does not belong to the essence of a thing, for existence is not an attribute or characteristic" (Posterior Analytics, Book II, Chapter VII, cited in The Fourfold Root of the Principle of Sufficient Reason, Section 7, "Descartes").
In fact, Gassendi had made a similar claim in the Fifth Objections. According to Gassendi, existence is not a property like omnipotence or any other property that is a perfection of God. Existence is what is needed for a property to be a property of something: "if a thing lacks existence, we do not say that it is imperfect, or deprived of a perfection, but say instead that it is nothing at all." To claim that God is the only thing for which existence is a perfection is to beg the question. If existence is a perfection, then any being with any perfection would have to be said to exist, but Descartes does not allow this conclusion.
Descartes rejects this criticism. He insists that he does not beg the question because he does not attribute mere existence to God, but rather necessary existence, something that is not attributable to anything else. Descartes adds that it is quite proper to consider existence as a property, because we should take "property" to refer to whatever can be predicated of something, as existence can be. God is omnipotent, and God necessarily exists.
We have noted that in the Third Meditation, Descartes had stated that he could not be completely certain of anything else unless he proved that God exists. At the end of the Fifth Meditation, he returns to this point, claiming that "certitude about other things is so dependent on [certainty that God exists] that without it nothing can ever be perfectly known."
The reason for this claim is that while he can be completely certain of the truth of what he clearly and distinctly perceives at the time he perceives it, he cannot be certain of it at other times unless he has two pieces of information: that he had perceived it clearly and distinctly, and that whatever he perceived clearly and distinctly is true. The second piece of information can be doubted (in moments he does not have the clear and distinct perception) unless he has knowledge of God's existence. Once he gains this knowledge, no counter-argument to what he believes can be raised.
In the Fourth Objections, Antoine Arnauld raised the question of whether Descartes has argued in a circle--the so-called "Cartesian circle."
My only remaining concern is whether the author does not commit a vicious circle, when he says that we have no other basis to establish that what we clearly and distinctly true, than that God exists.Descartes responded to this objection by appealing to account of "complete certainty" just given.
But we can be certain that God exists only because we clearly and evidently perceive this fact. Therefore, before we are certain that God exists, we ought to be certain that whatever we clearly and evidently perceive is true.
I have already given a sufficient explanation in the Reply to the Second Set of Objeections, sections 3 and 4, where I drew a distinction between what we are actually perceiving clearly and distinctly and what we recall having clearly perceived sometime earlier. For first of all it is manifest to us that God exists, since we are attending to the arguments that prove this; but later on, it is enough for us to recall our having clearly perceived something in order to be certain that it is true. This would not suffice, unless we knew that God exists and did not deceive us. (Replies to Fourth Objections
It is clear that the criticism in Second Objections is directed against Descartes's claim that he could not be completely certain of anything unless he knew that God exists. Thus, the objection goes, Descartes could not be certain of the existence of God unless he was certain of the existence of God. Descartes's answer to this question is appropriate.
But Arnauld was not concerned with the question of the certainty of beliefs based on clear and distinct perceptions which only only remembers to have had. Instead, his target is Descartes's claim in the "Synopsis" and Fourth Meditation that he could not know that what is clearly and distinctly perceived is true until he had proved God's existence. If Descartes's knowledge of God's existence is based on the truth of his clear and distinct perceptions, how could it arise unless it has already been established that God exists and is no deceiver?
There is a large body of literature containing attempts to find a way out of the circularity objection. For a very sophisticated attempt, see the article by Lex Newman in the Stanford Encyclopedia of Philosophy.
In the Sixth Meditation, we get the long-awaited proof of the existence of bodies. Because he requires an argument that is not subject to the slightest doubt, Descartes rejects any proof that relies on imagination and "sense perception," as yielding only probability. The argument from sense perception is that the existence of bodies would explain well the presence of images in his mind. The images would be understood as reproductions in our mind of external bodies. Moreover, the ideas found in "sense perception" occur in him against our will and are more intense than other ideas. This very probably is due to the influence of bodies, which are beyond the reach of his will and which act on him strongly. (Malebranche and Berkeley were to ask, though, why this kind of expanation yields any probability at all.)
To attain certainty, Descartes looked instead to his belief in the existence of bodies. As noted earlier, the will is indifferent as to what to believe: Something has to determine it in the direction of belief. Where this determination is very strong, the source must be found in our very makeup. This means that it must be attributed to God. Since God is no deceiver, our strong inclination to believe that bodies exist must be due to the fact that bodies do exist and that God wants us to believe this. As Hume was to point out, the route to bodies through God is "a very unexpected circuit" (Enquiry Concerning Human Undertanding, Section XII, Part I).
Having finally established that bodies exist, Descartes's final task is to show how his mind is related to the specific body he call his own. In the first place, Descartes maintained that the human mind and the human body are two completely distinct entities. This is an outcome of the Second Meditation. He could doubt that bodies exist while at the same time being certain that he himself, a thinking thing, exists. This shows that his mind and his body are different from each other and so can be made by God to exist separately. Descartes concludes that "because I have a clear and distinct idea of myself, insofar as I am merely a thinking thing and not an extended thing, and because on the other hand I have a distinct idea of a body, insofar as it is merely an extended thing and not a thinking thing, it is certain that I am really distinct from my body, and can exist without it" (Sixth Meditation). This being said, how are the two related to each other?
There are two models of the relation which Descartes used in various places. The first model is called upon early in the Sixth Meditation. This is the model of diffusion, where the mind is, as it were, spread out throughout the body. The reason for adopting this model is that we sense the body as if the mind were present throughout it, not in the manner of a pilot in a ship, who must rely on reports of his crew about the status of distant parts of the vessel. The second model, which is more prevelent toward the end of the Sixth Meditation, is that of a point of contact. According to this model, the mind is in touch with the body in a single place. Its knowledge of the rest of the body is the result of the communication of motion from its distant parts to the point of contact.
The diffusion model seems worse-suited to the strict separation of mind and body than does the point-of-contact model. A single point is unextended, in keeping with the nature of the mind. But how could a mind that is not extended be nonetheless spread out over an extended area? In response to Princess Elisabeth, Descartes proposed an analogy that he thought would help. We think of weight or gravity as spread out over an entire body, yet for the purposes of physics, we conceive it as concentrated in a single point. When pressed by Elisabeth, Descartes conceded with some irritation that perhaps the mind could be thought of as extended in some way different from being materially extended.
The point-of-contact model seems to have some positive virtues. Descartes could explain phenomena such as pain in an amputated limb by allowing that the motion that causes the pain originates higher-up in the body. Both the real and the phantom pain could be the result of motions at the point-of-contact (Descartes suggested that it is the pineal gland) that are indistinguishable from each other. But the point-of-contact model has its own difficulties. Here is Gassendi's assessment in the Fifth Objections
For if you are not greater than a point, how can you be united with the entire body, which is of such great magnitude? How, at least, can you be united with the brain, or some minute part of it, which (as has been said) must yet have some magnitude or extension, however small it be? If you are wholly without parts, how can you mix or appear to mix with its minute subdivisions? For there is no mixture unless each of the things to be mixed has part which can mix with one another?Descartes simply did not want to deal with these sorts of objections to his account of the relation between mind and body.
The final topic of the Meditations concerns errors in judgment that can in some way be attributed to the senses. As Descartes had pointed out earlier, sense itself is incapable of deception. It only presents images, which are then judged by the understanding. So God could not be considered a deceiver when he errs in these judgments, since he can constrain his judgment. On the other hand, he must admit that he has natural beliefs about bodies. The real value of the senses is that they allow him to determine the state of his body. When he feels a thirst, it is beneficial for him to drink fluids. This is not something that can be determined from his knowledge of the natures of bodies.
An apparent problem arises with such "natural" beliefs, however. There are times when natural beliefs lead us to harmful behavior. For example, a person suffering from dropsy (pooling of bodily fluids in the limbs) feels great thirst when drinking fluids would worsen his condition. God has made him so as to react in this way. So is God a deceiver after all? No, because this errant natural belief is the result of a malfunction in the body. The signals sent to the mind of a man with dropsy mimick those of someone in good health. This happens due to the complexity of the body, which itself is very useful. Besides, he has the capacity to overcome these natural beliefs through his use of reason. This even allows us to overcome the dream argument from Meditation I. He can compare his perceptions as to whether they form a connected whole, and when they do, he can be sure that he is not dreaming.
Descartes undertook to explain mathmatically all the phenomena of the physical universe, though he never completed his explanation of living things. The reasoning of the Meditations laid the foundation for this investigation. Our clear and distinct perceptions reveal the mathematical nature of physical bodies.
The chief vehicle of Cartesian explanation is motion. In the Principles of Philosophy, Descartes laid down a number of "laws" of motion. He considered them to be literally decrees of God that bodies behave in certain ways. Since they are based in God himself, they must conform to God's nature. So, for example, the law of inertia is traced to God's immutability.
Copernicus held that the earth moves around the sun. But he noticed that which body appeared to be at rest depends on the position of the observer. So while the sun appears to move from the earth, the earth would appear to move as seen from the sun. This fact was exploited by Galileo in his arguments for the motion of the earth.
Descartes held that bodies are nothing but extension in length, width, and breadth. This meant, for him, that bodies are in reality no different from space. (Part II, Sections 10-12). The external place of a space is defined by other spaces surrounding it. Now a body may be said to move (change its external place) when it changes its relation to those bodies defining its place. Thus, a man on a ship being carried out to sea is at rest relative to the ship but in motion relative to the shores. More strictly, though, we can define the place in terms of the boundary with immediately surrounding bodies (which may themselves change, as when a breeze blows air past a standing man). On this view, there can be no void or vacuum, since extension of space is identical to body.
A further consequence of this definition is that Descartes could deny the motion of the earth. He could hold that in the loose and arbitrary sense, the earth moves relative to the sun, but in the strict sense it does not. The reason is that the earth maintains the same position relative to its immediate boundaries. We can think of the atmosphere as such a boundary, or perhaps the small particles that make up the vortex in which the earth swirls (loosely speaking) around the sun.
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