Descartes' Ontological Argument (Stanford Encyclopedia of Philosophy) Cite this entry Search the SEP • Advanced Search • Tools • RSS FeedTable of Contents• What's New• Archives• Projected ContentsEditorial Information• About the SEP• Editorial Board• How to Cite the SEP• Special CharactersSupport the SEPContact the SEP ©Metaphysics Research Lab,CSLI,Stanford University  Open access to the SEP is made possible by a world-wide funding initiative. Please Read How You Can Help Keep the Encyclopedia FreeDescartes' Ontological ArgumentFirst published Mon Jun 18, 2001; substantive revision Sun Oct 15, 2006Descartes' ontological (or a priori) argument is both oneof the most fascinating and poorly understood aspects of hisphilosophy. Fascination with the argument stems from the effort toprove God's existence from simple but powerful premises. Existence isderived immediately from the clear and distinct idea of a supremelyperfect being. Ironically, the simplicity of the argument has alsoproduced several misreadings, exacerbated in part by Descartes' failureto formulate a single version.The main statement of the argument appears in the Fifth Meditation.This comes on the heels of an earlier causal argument for God'sexistence in the Third Meditation, raising questions about the orderand relation between these two distinct proofs. Descartes repeats theontological argument in a few other central texts including thePrinciples of Philosophy. He also defends it in the First,Second, and Fifth Replies against scathing objections by some of theleading intellectuals of his day.Descartes was not the first philosopher to formulate an ontologicalargument. An earlier version of the argument had been vigorouslydefended by St. Anselm in the eleventh century, and then criticized bya monk named Gaunilo (Anselm's contemporary) and later by St. ThomasAquinas (though his remarks were directed against yet another versionof the argument). Aquinas' critique was regarded as so devastating thatthe ontological argument died out for several centuries. It thus cameas a surprise to Descartes' contemporaries that he should attempt toresurrect it. Although he claims not to be familiar with Anselm'sversion of the proof, Descartes appears to craft his own argument so asto block traditional objections.Despite similarities, Descartes' version of the argument differsfrom Anselm's in important ways. The latter's version is thought toproceed from the meaning of the word "God," by definition, God is abeing a greater than which cannot be conceived. Descartes' argument, incontrast, is grounded in two central tenets of his philosophy — thetheory of innate ideas and the doctrine of clear and distinctperception. He purports not to rely on an arbitrary definition of Godbut rather on an innate idea whose content is "given." Descartes'version is also extremely simple. God's existence is inferred directlyfrom the fact that necessary existence is contained in the clear anddistinct idea of a supremely perfect being. Indeed, on some occasionshe suggests that the so-called ontological "argument" is not a formalproof at all but a self-evident axiom grasped intuitively by a mindfree of philosophical prejudice.Descartes often compares the ontological argument to a geometricdemonstration, arguing that necessary existence cannot be excluded fromidea of God anymore than the fact that its angles equal two rightangles, for example, can be excluded from the idea of a triangle. Theanalogy underscores once again the argument's supreme simplicity. God'sexistence is purported to be as obvious and self-evident as the mostbasic mathematical truth. It also attempts to show how the "logic" ofthe demonstration is rooted in our ordinary reasoning practices.In the same context, Descartes also characterizes the ontologicalargument as a proof from the "essence" or "nature" of God, arguing thatnecessary existence cannot be separated from the essence of a supremelyperfect being without contradiction. In casting the argument in theseterms, he is implicitly relying on a traditional medieval distinctionbetween a thing's essence and its existence. According to thistradition, one can determine what something is (i.e. its essence),independently of knowing whether it exists. This distinction appearsuseful to Descartes' aims, some have thought, because it allows him tospecify God's essence without begging the question of hisexistence. 1. The Simplicity of the "Argument"2. The Distinction between Essence and Existence3. Objections and RepliesBibliographyOther Internet ResourcesRelated Entries1. The Simplicity of the "Argument"One of the hallmarks of Descartes' version of the ontologicalargument is its simplicity. Indeed, it reads more like the report of anintuition than a formal proof. Descartes underscores the simplicity ofhis demonstration by comparing it to the way we ordinarily establishvery basic truths in arithmetic and geometry, such as that the numbertwo is even or that the sum of the angles of a triangle is equal to thesum of two right angles. We intuit such truths directly by inspectingour clear and distinct ideas of the number two and of a triangle. So,likewise, we are able to attain knowledge of God's existence simply byapprehending that necessary existence is included in the clear anddistinct idea of a supremely perfect being. As Descartes writes in theFifth Meditation:[1] But if the mere fact that I can produce from my thoughtthe idea of something entails that everything which I clearly anddistinctly perceive to belong to that thing really does belong to it,is not this a possible basis for another argument to prove theexistence of God? Certainly, the idea of God, or a supremely perfectbeing, is one that I find within me just as surely as the idea of anyshape or number. And my understanding that it belongs to his naturethat he always exists is no less clear and distinct than is the casewhen I prove of any shape or number that some property belongs to itsnature (AT 7:65; CSM 2:45).One is easily misled by the analogy between the ontological argumentand a geometric demonstration, and by the language of "proof" in thispassage and others like it. Descartes does not conceive the ontologicalargument on the model of an Euclidean or axiomatic proof, in whichtheorems are derived from epistemically prior axioms and definitions.On the contrary, he is drawing our attention to another method ofestablishing truths that informs our ordinary practices and isnon-discursive. This method employs intuition or, what is the same forDescartes, clear and distinct perception. It consists in unveiling thecontents of our clear and distinct ideas. The basis for this method isthe rule for truth, which was previously established in the FourthMeditation. According to the version of this rule invoked in the FifthMeditation, whatever I clearly and distinctly perceive to be containedin the idea of something is true of that thing. So if I clearly anddistinctly perceive that necessary existence pertains to the idea of asupremely perfect being, then such a being truly exists.Although Descartes maintains that God's existence is ultimatelyknown through intuition, he is not averse to presenting formal versionsof the ontological argument. He never forgets that he is writing for aseventeenth-century audience, steeped in scholastic logic, that wouldhave expected to be engaged at the level of the Aristotelian syllogism.Descartes satisfies such expectations, presenting not one but at leasttwo separate versions of the ontological argument. These proofs,however, are stunningly brief and betray his true intentions. Oneversion of the argument simply codifies the psychological process bywhich one intuits God's existence, in the manner described above:Version A: Whatever I clearly and distinctly perceive to be contained in theidea of something is true of that thing.I clearly and distinctly perceive that necessary existence iscontained in the idea of God.Therefore, God exists.The rule for truth appears here in the guise of the first premise,but it is more naturally read as a statement of Descartes' ownalternative method of "demonstration" via clear and distinct perceptionor intuition. In effect, the first "premise" is designed to instructthe meditator on how to apply this method, the same role that theanalogy with a geometric demonstration serves in passage [1].When presenting this version of the argument in the First Replies,Descartes sets aside this first premise and focuses our attention onthe second. In so doing, he is indicating the relative unimportance ofthe proof itself. Having learned how to apply Descartes' alternativemethod of reasoning, one need only perceive that necessary existencepertains to the idea of a supremely perfect being. Once one attainsthis perception, formal arguments are no longer required; God'sexistence will be self-evident (Second Replies, Fifth Postulate; AT7:163-4; CSM 2:115).Descartes sometimes uses traditional arguments as heuristic devices,not merely to appease a scholastically trained audience but to helpinduce clear and distinct perceptions. This is evident for example inthe version of the ontological argument standardly associated with hisname:Version B: I have an idea of supremely perfect being, i.e. a being having allperfections.Necessary existence is a perfection.Therefore, a supremely perfect being exists.While this set of sentences has the surface structure of a formalargument, its persuasive force lies at a different level. A meditatorwho is having trouble perceiving that necessary existence is containedin the idea of a supreme perfect being can attain this perceptionindirectly by first recognizing that this idea includes everyperfection. Indeed, the idea of a supremely perfect being just is theidea of a being having all perfections. To attempt to exclude any orall perfections from the idea of a supremely being, Descartes observes,involves one in a contradiction and is akin to conceiving a mountainwithout a valley (or, better, an up-slope without a down-slope). Havingformed this perception, one need only intuit that necessary existenceis itself a perfection. It will then be clear that necessary existenceis one of the attributes included in the idea of a supremely perfectbeing.While such considerations might suffice to induce the requisiteclear and distinct perception in the meditator, Descartes is aiming adeeper point, namely that there is a conceptual link between necessaryexistence and each of the other divine perfections. It is important torecall that in the Third Meditation, in the midst of the causalargument for the existence of God, the meditator already discoveredmany of these perfections — omnipotence, omniscience, immutability,eternality, simplicity, etc. Because our mind is finite, we normallythink of the divine perfections separately and "hence may notimmediately notice the necessity of their being joined together" (FirstReplies, AT 7:119; CSM 2:85). But if we attend carefully to "whetherexistence belongs to a supremely perfect being, and what sort ofexistence it is" we shall discover that we cannot conceive any one ofthe other attributes while excluding necessary existence from it(ibid.).To illustrate this point Descartes appeals to divine omnipotence. Hethinks that we cannot conceive an omnipotent being except as existing.Descartes' illustration presupposes the traditional, medievalunderstanding of "necessary existence." When speaking of this divineattribute, he sometimes uses the term "existence" simpliciteras shorthand. But in his more careful pronouncements he always insistson the phrase "necessary and eternal existence," which resonates withtradition. Medieval, scholastic philosophers often spoke of God as thesole "necessary being," by which they meant a being who depends only onhimself for his existence (a se esse). This is the notion of"aseity" or self-existence. Since such a being does not depend onanything else for its existence, he has neither a beginning nor an end,but is eternal. Returning to the discussion in the First Replies, onecan see how omnipotence is linked conceptually to necessary existencein this traditional sense. An omnipotent or all-powerful being does notdepend ontologically on anything (for if it did then it would not beomnipotent). It exists by its own power:[2] when we attend to immense power of this being, we shallbe unable to think of its existence as possible without alsorecognizing that it can exist by its own power; and we shall infer fromthis that this being does really exist and has existed from eternity,since it is quite evident by the natural light that what can exist byits own power always exists. So we shall come to understand thatnecessary existence is contained in the idea of a supremely perfectbeing ... . (ibid.)Some readers have thought that Descartes offers yet a third versionof the ontological argument in this passage (Wilson, 1978, 174-76), butwhether or not that was his intention is unimportant, since his primaryaim, as indicated in the last line, is to enable his meditator tointuit that necessary existence is included in the idea of God. Sincethere is a conceptual link between the divine attributes, a clear anddistinct perception of one provides a cognitive route to any of theothers.Although Descartes sometimes uses formal versions of the ontologicalargument to achieve his aims, he consistently affirms that God'sexistence is ultimately known through clear and distinct perception.The formal versions of the argument are merely heuristic devices, to bejettisoned once has attained the requisite intuition of a supremelyperfect being. Descartes stresses this point explicitly in the FifthMeditation, immediately after presenting the two versions of theargument considered above:[3] whatever method of proof I use, I am always broughtback to the fact that it is only what I clearly and distinctly perceivethat completely convinces me. Some of the things I clearly anddistinctly perceive are obvious to everyone, while others arediscovered only by those who look more closely and investigate morecarefully; but once they have been discovered, the latter are judged tobe just as certain as the former. In the case of a right-angledtriangle, for example, the fact that the square on the hypotenuse isequal to the square on the other two sides is not so readily apparentas the fact that the hypotenuse subtends the largest angle; but onceone has seen it, one believes it just as strongly. But as regards God,if I were not overwhelmed by philosophical prejudices, and if theimages of things perceived by the senses did not besiege my thought onevery side, I would certainly acknowledge him sooner and more easilythan anything else. For what is more manifest than the fact that thesupreme being exists, or that God, to whose essence alone existencebelongs, exists? (AT 7:68-69; CSM 2:47)Here Descartes develops his earlier analogy between the (so-called)ontological argument and a geometric demonstration. He suggests thatthere are some meditators for whom God's existence is immediatelymanifest; for them God's existence is akin to an axiom or definition ingeometry, such as that the hypotenuse of a right triangle subtends itslargest angle. But other meditators, whose minds are confused and miredin sensory images, must work much harder, and might even require aproof to attain the requisite clear and distinct perception. For them,God's existence is akin to the Pythagorean Theorem. The important pointis that both kinds of meditators ultimately attain knowledge of God'sby clearly and distinctly perceiving that necessary existence iscontained in the idea of supremely perfect being. Once one has achievedthis perception, God's existence will be manifest or, as Descartes sayselsewhere, "self-evident" (per se notam) (Second Replies,Fifth Postulate; AT 7: 164; CSM 2:115).Descartes' contemporaries would have been surprised by this lastremark. While reviewing an earlier version of the ontological argument,Aquinas had rejected the claim that God's existence is self-evident, atleast with respect to us. He argued that what is self-evident cannot bedenied without contradiction, but God's existence can be denied.Indeed, the proverbial fool says in his heart "There is no God" (Psalm53.1).When confronted with this criticism by a contemporary objector,Descartes tries to find common ground: "St. Thomas asks whetherexistence is self-evident as far as we are concerned, that is, whetherit is obvious to everyone; and he answers, correctly, that it is not"(First Replies, AT 7:115; CSM 2:82). Descartes interprets Aquinas to beclaiming that God's existence is not self-evident to everyone,which is something with which he can agree. Descartes does not holdthat God's existence is immediately self-evident, or self-evident toeveryone, but that it can become self-evident to some careful andindustrious meditators.[Return to Section links]2. The Distinction between Essence and ExistenceIn the Fifth Meditation and elsewhere Descartes says that God'sexistence follows from the fact that existence is contained in the"true and immutable essence, nature, or form" of a supremely perfectbeing, just as it follows from the essence of a triangle that itsangles equal two right angles. This way of putting the apriori argument has puzzled commentators and has led to a livelydebate about the ontological status of Cartesian essences and theobjects which are purported to "have" them. Some commentators havethought that Descartes is committed to a species of Platonic realism.According to this view, some objects that fall short of actualexistence nevertheless subsist as abstract, logical entities outsidethe mind and beyond the physical world (Kenny, 1968; Wilson, 1978).Another commentator places Cartesian essences in God (Schmaltz 1991),while two recent revisionist interpretations (Chappell, 1997; Nolan,1997) read Descartes as a conceptualist who takes essences to be ideasin human minds.Descartes' reference to "essences" raises another important issuemore directly related to the ontological argument. In claiming thatnecessary existence cannot be excluded from the essence of God,Descartes is drawing on the traditional medieval distinction betweenessence and existence. According to this distinction, one can saywhat something is (i.e. its essence), prior to knowing whetherit exists. So, for example, one can define what a horse is —enumerating all of its essential properties — before knowing whetherthere are any horses in the world. The only exception to thisdistinction was thought to be God himself, whose essence just is toexist. It is easy to see how this traditional distinction could beexploited by a defender of the ontological argument. Existence isincluded in the essence of a supremely perfect being, but not in theessence of any finite thing. Thus it follows solely from the essence ofthe former that such a being actually exists. At times, Descartesappears to support this interpretation of the ontological argument. Inthe Fifth Replies, for example, he writes that "the existence of atriangle should not be compared with the existence of God, since therelation between existence and essence is manifestly quite different inthe case of God from what it is in the case of the triangle. God is hisown existence, but this is not true of the triangle" (AT 7:383; CSM2:263). But Descartes' complete view is subtler and more sophisticatedthan these remarks first suggest. Understanding this view requires amore careful investigation of the distinction between essence andexistence as it appears in medieval sources. Although one often speaksof the "traditional" distinction, the exact nature of the relationbetween essence and existence in finite things was the subject of afierce debate among medieval philosophers. Seeing where Descartes'position fits within this debate will provide a deeper understanding ofhis version of the ontological argument.The distinction between essence and existence can be traced back asfar as Boethius in the fifth century. It was later developed by Islamicthinkers such as Avicenna. But the issue did not become a majorphilosophical problem until it was taken up by Aquinas in thethirteenth century. The issue arose not as part of an effort toestablish God's existence on a priori grounds (as mentionedabove, Aquinas was one of the staunchest critics of the ontologicalargument), but out of concern to distinguish God from finite spiritualentities such as angels. Like many scholastic philosophers, Aquinasbelieved that God is perfectly simple and that created beings, incontrast, have a composite character that accounts for their finitudeand imperfection. In the case of purely spiritual or nonmaterialcreatures, he attempted to locate this character in the composition ofessence and existence.Some of the details of Aquinas' account will emerge from ourdiscussion below. The primary interest of his theory for our purposes,however, is that it led to a lively debate among his successors both asto how to interpret the master and about the true nature of therelation between essence and existence in created things. This debateproduced three main positions:The Theory of Real DistinctionThe Intermediate PositionThe Theory of Rational DistinctionProponents of the first view conceived the distinction betweenessence and existence as obtaining between two separate things. In theeyes of many Thomists, this view was considered to be quite radical,especially as an interpretation of Aquinas' original position. Thelatter is sometimes expressed by saying that essence and existence are"principles of being" rather than beings themselves. One problem withthe theory of real distinction then was that it reified essence andexistence, treating them as real beings in addition to the createdentity that they compose.The theory of real distinction was also considered objectionable forphilosophical reasons. Following Aquinas, many participants in thedebate urged that essence and existence are related to each other aspotency and act, so that existence can be said to "actualize" essence.On the theory of real distinction, this view leads to an infiniteregress. If an essence becomes actual only in virtue of something else— viz. existence — being superadded to it, then what givesexistence its reality, and so on ad infinitum? (Wippel, 1982,393f).In response to these difficulties some scholastic philosophersdeveloped a position at the polar extreme from the theory of realdistinction. This was the view that there is merely a rationaldistinction or a "distinction of reason" between essence and existencein created beings. As the term suggests, this theory held that essenceand existence of a creature are identical in reality and distinguishedonly within our thought by means of reason. Needless to say, proponentsof this theory were forced to distinguish purely spiritual entitiesfrom God on grounds other than real composition.Giving up the doctrine of real composition seemed too much foranother group of thinkers who were also critical of the theory of realdistinction. This led to the development of a number of intermediatepositions. One such position was that essence and existence are modallyor formally distinct, such that existence constitutes a mode orproperty of a thing's essence.Like Francisco Suárez, his most immediate scholasticpredecessor, Descartes sides with the proponents of a rationaldistinction between essence and existence. His position is unique,however, insofar as it springs from a more general theory of"attributes". Articulating this theory in an important passage in thePrinciples of Philosophy, Descartes claims that there ismerely a distinction of reason between a substance and any one of itsattributes or between any two attributes of a single substance (1:62,AT 8A:30; CSM 1:214). For Descartes' purposes, the most significantinstance of a rational distinction is that which obtains between asubstance and its essence — or what he sometimes refers to as its"principal attribute" (1:53, AT 8A:25; CSM 1:210). Since thought andextension constitute the essence of mind and body, respectively, a mindis merely rationally distinct from its thinking and a body is merelyrationally distinct from its extension (1:63, AT 8A:31; CSM 1:215). ButDescartes insists that a rational distinction also obtains between anytwo attributes of a substance. Since existence qualifies as anattribute in this technical sense, the essence and existence of asubstance are also distinct merely by reason (1:56, AT 8A:26; CSM1:211). Descartes reaffirms this conclusion in a letter intended toelucidate his account of the relation between essence andexistence:[4]... existence, duration, size, number and all universalsare not, it seems to me, modes in the strict sense ... . They arereferred to by a broader term and called attributes ... because we doindeed understand the essence of a thing in one way when we consider itin abstraction from whether it exists or not, and in a different waywhen we consider it as existing; but the thing itself cannot be outsideour thought without its existence ... . Accordingly I say that shapeand other similar modes are strictly speaking modally distinct from thesubstance whose modes they are; but there is a lesser distinctionbetween the other attributes ... . I call it a rational distinction .... (To an unknown correspondent, AT 4:349; CSMK 3:280)Indications are given here as to how a rational distinction isproduced in our thought. Descartes explains that we regard a singlething in different abstract ways. Case in point, we can regard a thingas existing, or we can abstract from its existence and attend to itsother aspects. In so doing, we have distinguished the existence of asubstance from its essence within our thought. Like scholasticproponents of the theory of rational distinction, however, Descartes iskeen to emphasize that this distinction is purely conceptual. Indeed,he goes on to explain that the essence and existence of a substance are"in no way distinct" outside thought (AT 4:350; CSMK 3:280). In realitythey are identical.While borrowing much from scholasticism, Descartes' account isdistinguished by its scope of application. He extends the theory ofrational distinction from created substances to God. In general, theessence and the existence of a substance are merely rationallydistinct, and hence identical in reality.This result appears to wreak havoc on Descartes' ontologicalargument. One of the most important objections to the argument is thatif it were valid, one could proliferate such arguments for all sorts ofthings, including beings whose existence is merely contingent. Bysupposing that there is merely a rational distinction between essenceand existence abroad in all things, Descartes seems to confirm thisobjection. In general, a substance is to be identified with itsexistence, whether it is God or a finite created thing.The problem with this objection, in this instance, is that itassumes that Descartes locates the difference between God and creaturesin the relation each of these things bears to its existence. This isnot the case. In a few important passages, Descartes affirms thatexistence is contained in the clear and distinct idea of every singlething, but he also insists that there are different grades ofexistence:[5] Existence is contained in the idea or concept of everysingle thing, since we cannot conceive of anything except as existing.Possible or contingent existence is contained in the concept of alimited thing, whereas necessary and perfect existence is contained inthe concept of a supremely perfect being (Axiom 10, Second Replies; AT7:166; CSM 2:117).In light of this passage and others like it, we can refine thetheory of rational distinction. What one should say, strictly speaking,is that God is merely rationally distinct from his necessaryexistence, while every finite created thing is merely rationallydistinct from its possible or contingent existence.The distinction between possible or contingent existence on the onehand, and necessary existence on the other, allows Descartes to accountfor the theological difference between God and his creatures.Now, when Descartes says that a substance (be it finite or infinite)is merely rationally distinct from its existence, he always means anactually existing substance. So how are we to understand the claim thata finite substance is merely rationally distinct from itspossible existence? What is meant by "possible (or contingent)existence"? It is tempting to suppose that this term means non-actualexistence. But as we saw already with the case of necessary existence,Descartes does not intend these terms in their logical or modal senses.If "necessary existence" means ontologically independent existence,then "possible existence" means something like dependentexistence. After all, Descartes contrasts possible existence not withactual existence but with necessary existence in the traditional sense.This account is also suggested by the term "contingent." Created thingsare contingent in the sense that they depend for their existence onGod, the sole independent being.This result explains why Descartes believes that we cannotproliferate ontological arguments for created substances. It is notthat the relation between essence and existence is any different in Godthan it is in finite things. In both cases there is merely a rationaldistinction. The difference is in the grade of existence that attachesto each. Whereas the concept of an independent being entails that sucha being exists, the concept of a finite thing entails only that it hasdependent existence.Looking back at the problematic passage cited above from the FifthReplies, it becomes clear that Descartes intended something along theselines even there. He says that "the existence of a triangle should notbe compared with the existence of God", reinforcing the point that itis the kind of existence involved that makes God unique. And justbefore this statement, he writes, "in the case of God necessaryexistence...applies to him alone and forms a part of his essence as itdoes of no other thing". Later he adds: "I do not ... deny thatpossible existence is a perfection in the idea of a triangle, just asnecessary existence is perfection in the idea of God" (AT 7:383; CSM2:263). Descartes' final position then is that essence and existenceare identical in all things. What distinguishes God from creatures ishis grade of existence. We can produce an ontological argument for God,and not for finite substances, because the idea of a supremely perfectbeing uniquely contains necessary — or ontologically independent —existence.[Return to Section links]3. Objections and RepliesBecause of its simplicity, Descartes' version of the ontologicalargument is commonly thought to be cruder and more obviously fallaciousthan the one put forward by Anselm in the eleventh century. But whenthe complete apparatus of the Cartesian system is brought forth, theargument proves itself to be quite resilient, at least on its ownterms. Indeed, Descartes' version is superior to his predecessor'sinsofar as it is grounded in a theory of innate ideas and the doctrineof clear and distinct perception. These two doctrines inoculateDescartes from the charge made against Anselm, for example, that theontological argument attempts to define God into existence byarbitrarily building existence into the concept of a supremely perfectbeing. In the Third Meditation, the meditator discovers that her ideaof God is not a fiction that she has conveniently invented butsomething native to the mind. As we shall see below, these twodoctrines provide the resources for answering other objections aswell.Given our earlier discussion concerning the non-logical status ofthe ontological argument, it may seem surprising that Descartes wouldtake objections to it seriously. He should be able to dismiss mostobjections in one neat trick by insisting on the non-logical nature ofthe demonstration. This is especially true of objection that theontological argument begs the question. If God's existence isultimately self-evident and known by a simple intuition of the mind,then there are no questions to be begged. Unfortunately, not all of theobjections to the ontological argument can be dismissed so handily, forthe simple reason that they do not all depend on the assumption that weare dealing with a formal proof.Although it is often overlooked, many of the best known criticismsof the ontological argument were put to Descartes by official objectorsto the Meditations. He in turn responded to these objections— sometimes in lengthy replies — though many contemporary readershave found his responses opaque and unsatisfying. We can betterunderstand his replies and, in some cases, improve upon them byappealing to discussions from previous sections.One classical objection to the ontological argument, which was firstleveled by Gaunilo against Anselm's version of the proof, is that itmakes an illicit logical leap from the mental world of concepts to thereal world of things. The claim is that even if we were to concede thatnecessary existence is inseparable from the idea of God (in Kant'sterms, even if necessary existence were analytic of the concept "God"),nothing follows from this about what does or does not exist in theactual world. Johannes Caterus, the author of the First Set ofObjections to the Meditations, puts the point as follows:[6] Even if it is granted that a supremely perfect beingcarries the implication of existence in virtue of its very title, itstill does not follow that the existence in question is anything actualin the real world; all that follows is that the concept of existence isinseparably linked to the concept of a supreme being. So you cannotinfer that the existence of God is anything actual unless you supposethat the supreme being actually exists; for then it will actuallycontain all perfections, including the perfection of real existence (AT7:99; CSM 2:72).To meet this challenge, Descartes must explain how he "bridges" theinferential gap between thought and reality. The principle of clear anddistinct perception is intended to do just that. According to thisprinciple, for which he argues in the Fourth Meditation, whatever oneclearly and distinctly perceives or understands is true — true notjust of ideas but of things in the real world represented by thoseideas. Thus, Descartes' commitment to the principle of clear anddistinct perception allows him to elude another objection that hadhaunted Anselm's version of the argument.The previous objection is related to another difficulty raised byCaterus. In order to illustrate that the inference from the mental tothe extra-mental commits a logical error, critics have observed that ifsuch inferences were legitimate then we could proliferate ontologicalarguments for supremely perfect islands, existing lions, and all sortsof things which either do not exist or whose existence is contingentand thus should not follow a priori from their concept. Thetrick is simply to build existence into the concept. So while existencedoes not follow from the concept of lion per se, it doesfollow from the concept of an "existing lion."Descartes' actual reply to this objection, which he took veryseriously, is highly complex and couched in terms of a theory of "trueand immutable natures." We can simplify matters by focusing on its keyelements. One of his first moves is to introduce a point that wediscussed earlier (see passage [5] in section 2),namely that existence is contained in the idea of every thing that weclearly and distinctly perceive: possible (or dependent) existence iscontained in our clear and distinct idea of every finite thing andnecessary (or independent) existence is uniquely contained in the ideaof God (AT 7:117; CSM 2:83). So for Descartes one does not have tobuild existence into the idea of something if that idea is clear anddistinct; existence is already included in every clear and distinctidea. But it does not follow that the thing represented by such an ideaactually exists, except in the case of God. We cannot produceontological arguments for finite things for the simple reason that theclear and distinct ideas of them contain merely dependent existence.Actual existence is demanded only by the idea of God, which uniquelycontains independent existence.A natural rejoinder to this reply would be to ask about the idea ofa lion having not possible but wholly necessary existence. IfDescartes' method of reasoning were valid, it would seem to follow fromthis idea that such a creature exists. This formulation of theobjection requires Descartes' second and deeper point, which is onlyhinted at in his official reply. This is that the idea of a lion — letalone the idea of a lion having necessary existence — is hopelesslyobscure and confused. As Descartes says, the nature of a lion is "nottransparently clear to us" (Axiom 10, Second Replies; AT 7:117; CSM2:84). Since this idea is not clear and distinct, the method ofdemonstration employed in the ontological argument does not apply toit. Recall that the geometrical method of demonstration is grounded inthe principle of clear and distinct perception and consists in drawingout the contents of our clear and distinct ideas. If an idea is notclear and distinct then we cannot draw any conclusions from it aboutthings outside thought.The key difference then between the idea of God on the one hand andthe idea of a necessarily existing lion is that the former can beclearly and distinctly perceived. For Descartes, it is just a brutefact that certain ideas can be clearly and distinctly perceived andothers cannot. Some critics have charged him with dogmatism in thisregard. Why should Descartes be allowed to legislate the scope of ourclear and distinct perceptions? Perhaps we can clearly and distinctlyperceive something that he could not.Descartes cannot be saved entirely from this charge, but twoimportant points can be made in his defense. First, he has principledreasons for thinking that everyone has the same set of innate or clearand distinct ideas. When the meditator first proved God's existence inthe Third Meditation, she also established that God is supremely goodand hence no deceiver. One consequence of God's perfect benevolence isthat he implanted the same set of innate ideas in all finite minds.Thus, Descartes feels justified in concluding that the limits of hiscapacity for clear and distinct perception will be shared byeveryone.Second, when responding to objections to the ontological argumentsuch as the ones considered above, Descartes typically does more thaninsist dogmatically on a unique set of clear and distinct ideas. Healso tries to dispel the confusion which he thinks is at the root ofthe objection. Since the ontological argument ultimately reduces to anaxiom, the source of an objection according to Descartes' diagnosis isthe failure of the objector to perceive this axiom clearly anddistinctly. Thus, Descartes devotes the bulk of his efforts to tryingto remove those philosophical prejudices which are hindering hisobjector from intuiting the axiom. These efforts are not alwaysobvious, however. Descartes is good at maintaining the pretense ofanswering criticisms to a formal proof. But his replies to Caterus'objections to the ontological argument are best read as an extendedeffort to dispel prejudice and confusion, so as to enable his reader tointuit God's existence for himself.Perhaps the most interesting objection to the ontological argument,and the one that has received the most attention since being formulatedby Immanuel Kant, is that existence is not a property or predicate.This objection enjoys the status of a slogan known by everyundergraduate philosophy major worth her salt. In claiming thatexistence is included in the idea of a supremely perfect being, alongwith all the other divine attributes, Descartes' version of theargument appears to succumb to this objection.It is not obvious of course that existence is not apredicate. To convince us of this point, Kant observes that there is nointrinsic difference between the concept of a hundred real thalers(coins common in Kant's time) and the concept of a hundred possiblethalers. Whenever we think of anything, we regard it asexisting, even if the thing in question does not actually exist. Thus,existence does not add anything to the concept of a thing. What then isexistence if not a predicate? Kant's answer is that existence is"merely the positing of a thing" or "the copula of a judgment," thepoint being that when we say "God exists" we are simply affirming thatthere is an object answering to the concept of God. We are notascribing any new predicates to God, but merely judging that there is asubject, with all its predicates, in the world (CPR:B626-27).Kant's formulation of the objection was later refined by BertrandRussell in his famous theory of descriptions. He argues thatexistential statements such as "God exists" are misleading as to theirlogical form. While serving grammatically as a predicate, the term"exists" in this sentence has a much different logical function, whichis revealed only by analysis. Properly analyzed, "God exists" means"there is one (and only one) x such that ‘x is omnipotent,omniscient, etc.’ is true." Russell thinks this translation showsthat, appearances to the contrary, the statement "God exists" is notascribing existence to a subject, but asserting that a certaindescription (in single quotes) applies to something in reality.Russell's view is reflected in the standard modern logical treatment ofexistence as a quantifier rather than a predicate.It is widely believed that Descartes did not have a response to thisobjection, indeed that he blithely assumed that existence is a propertywithout ever considering the matter carefully. But this is not thecase. The seventeenth-century empiricist Pierre Gassendi confrontedDescartes with this criticism in the Fifth Set of Objections (andprobably deserves credit for being the first to enunciate it):"existence is not a perfection either in God or in anything else; it isthat without which no perfections can be present" (AT 7:323; CSM2:224). As with most of his replies to Gassendi (whom he regarded as aloathsome materialist and quibbler), Descartes responded somewhatcurtly. But it is clear from the discussion in section 2 that he hadthe resources for addressing this objection in a systematic manner.Before examining how Descartes might defend himself, it is importantto note that the question at issue is typically framed in non-Cartesianterms and thus often misses its target. Both Kant and Russell forexample are interested in the logical issue of whether existence is apredicate. Descartes, in contrast, was not a logician anddisparaged the standard subject-predicate logic inherited fromAristotle. Although, as discussed above, he sometimes presents formalversions of the ontological arguments as heuristic devices, Descartesthought that God's existence is ultimately known through intuition.This intuitive process is psychological in character. It is not amatter of assigning predicates to subjects but of determining whetherthe idea of a supremely perfect being can be clearly and distinctlyperceived while excluding necessary existence from it through a purelyintellectual operation. To be sure, Descartes was interested in theontological question of whether existence is a "property" ofsubstances. For him, however, the analogues of properties are clear anddistinct ideas and ways of regarding them, not predicates.Having said that, Descartes' best strategy for answering theontological version of the objection is to concede it, or at leastcertain aspects of it. Descartes explicitly affirms Kant's point thatexistence does not add anything to the idea of something (provided thatthe terms "idea" and "concept" are regarded as psychological items).Once again we should recall passage [4] from the Second Replies:"Existence is contained in the idea or concept of every single thing,since we cannot conceive of anything except as existing" (Axiom 10, AT7:166; CSM 2:117). So Descartes agrees with Kant that there is noconceptual difference between conceiving a given substance as actuallyexisting and conceiving it as merely possible. In the first instanceone is attending to the existence that is contained on every clear anddistinct idea, and in the other instance one is ignoring the thing'sexistence without actively excluding it. He would, however, stressanother conceptual difference that Kant and other critics do notaddress, namely that between the two grades of existence — contingentand necessary. The clear and distinct ideas of all finite thingscontain merely contingent or dependent existence, whereas the clear anddistinct idea of God uniquely contains necessary or wholly independentexistence (ibid.). As discussed previously, the ontological argumenthinges on this distinction.Another intuition underlying the claim that existence is not aproperty is that there is more intimate connection between anindividual and its existence than the traditional one between asubstance and a property, especially if the property in question isconceived as something accidental. If existence were accidental, then athing could be without its existence, which seems absurd. It seems noless absurd to say that existence is a property among other properties(accidental or essential), for how can a thing even have properties ifit does not exist? Descartes shares this intuition. He does not thinkthat existence is a property in the traditional sense or is evendistinct from the substance that is said to bear it. Recall the viewdiscussed in section 2 that there is merely a rational distinctionbetween a substance and its existence, or between the essence andexistence of a substance. This means that the distinction between asubstance and its existence is confined to thought or reason. Humanbeings, in their efforts to understand things using their finiteintellects, draw distinctions in thought that do not obtain in reality.In reality, a substance (whether it be created or divine) just is itsexistence.The purpose of this defense of Descartes is not to render a verdictas whether he has the correct account of existence, but to show that hehad a rather sophisticated and systematic treatment of what has beenone of the great bugbears in the history of philosophy. He did notmake the ad hoc assumption that existence is an attribute inorder to serve the needs of the ontological argument. Indeed, onDescartes' view, existence is not a property in the traditional sense,nor can one conceive something without regarding it as existing.Descartes' critics might not be convinced by his account of existence,but then they have the burden of providing a better account. The focusof the debate will then be shifted to the question of who has thecorrect ontology, rather than whether the ontological argument perse is sound.[Return to Section links]BibliographyPrimary TextsAdam, Charles, and Paul Tannery. 1964-1976. Oeuvres deDescartes, vols. I-XII, revised edition. Paris: J. Vrin/C.N.R.S.[references to this work (abbreviated as "AT") are by volume and page,separated by a colon.]Cottingham, John, Robert Stoothoff, Dugald Murdoch, and (for vol.3) Anthony Kenny, eds. and trans. 1984. The Philosophical Writingsof Descartes, vols. 1-3. 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