U of Vic Philosophy Student Union
The Role Of God In Descartes’ Epistemic Theory

By Adrian M. Viens

The existence of God, and more importantly God’s role in our lives, has been a long and varied topic throughout the history of philosophy. René Descartes’ (1596-1650) epistemological contribution to Western philosophy was his attempt to establish a rational method of inquiry whereby knowledge about the world could be derived independent from the authority of the Church or the Bible. However, Descartes’ project was not to remove God from our lives; on the contrary, Descartes attempts to prove the existence of God, and to establish that only God can guarantee certain and true knowledge. Through a critical examination of the arguments advanced by Descartes in his most prominent work, Meditations on First Philosophy, regarding the existence of God and the role God plays in the acquisition of certain knowledge, we are able to see that although the goals of the Cartesian project were laudable, the presence of numerous philosophical inconsistencies and presumptive conjecture weakened its validity beyond repair.

Ontological Proof for the Existence of God

The establishment of the existence of God is absolutely essential to Descartes’ epistemic project. In the course of Descartes’ method of systematic doubt and absolute rejection of the products of sense experience, it is necessary for Descartes to prove the existence of God without referring to evidence from the perceptual world (e.g. The Bible, miracles, etc.). In the fifth meditation, Descartes advances a proof for the existence of God using reason alone. Descartes maintains that there are ideas of particular objects or entities in our minds that are demonstrable, yet have not been experienced.

What I believe must be considered above all here is the fact that I find within me countless ideas of certain things, that, even if perhaps they do not exist anywhere outside of me, still cannot be said to be nothing. And although, in a sense, I think them at will, nevertheless they are not something I have fabricated; rather they have their own true and immutable natures. (Descartes 5:42-43)

Descartes initially uses the concept of a triangle (i.e. three-sided figure, internal angles summing to 180 degrees, etc.) to illustrate an entity whose "nature, essence, or form" is independent from our minds or sense experience, yet we do not question that it indeed exists.

Descartes will use this notion — the idea in our minds can be used to prove the existence of entities — in his ontological proof for the existence of God. On Descartes’ account, "…from the mere fact that I can bring forth from my thought the idea of something, it follows that all that I clearly and distinctly perceive to belong to that thing really does belong to it, then cannot this too be a basis for an argument proving the existence of God?" (Descartes 5:43) Under this conception, it is the actual presence of a theoretical entity in the mind that will lay the groundwork for the argument for the existence of God. Yet this will not be sufficient for Descartes, for we can imagine theoretical entities such as unicorns that we know do not exist. Descartes will have account for the placement of a theoretical concept of a particular entity in the mind and the presence of this entity in the physical (or metaphysical) world.

The concept of God Descartes is trying to advance is based on the monotheist Christian notion of a supremely perfect being. Most Western intellectual contemporaries of Descartes, whether atheists or believers, were aware of this particular concept of God and would, in all likelihood, not have objected to the advancement of this concept. In the development of this concept, we are assured that a supreme being lacking in nothing would obviously possess the property of existence. Hence, the conception of a perfect God in our imagination, who as a perfect entity would have to exist, "…ought to have for me at least the same degree of certainty that truths of mathematics had until now." (Descartes 5:44) As a supremely perfect entity being all-powerful, all-knowing, etc., at its core, all of these perfect properties would be meaningless without the existence. Thus for Descartes, when we think about the essence of God, existence is inseparable.

To Descartes’ credit, he acknowledges possible criticism in his line of reasoning by admitting that his argumentation may have a "sophistic" tinge with respect to the notion of existence as the essence of God. However, Descartes believes that his arguments can proceed without serious difficulty because

…it is obvious to anyone who pays close attention that existence can no more be separated from God’s essence that its having three angles equal to two right angles can be separated from the essence of a triangle, or than the idea of a valley can be separated from the idea of a mountain). Thus it is no less contradictory to think of God (that is, a supremely perfect being) lacking existence (that is, lacking some perfection) than it is to think of a mountain without a valley. (Descartes 5:44)

This is the crux of the ontological argument for the existence of God. Once we accept the concept of a perfect God, we are unable to rationally deny the existence of that entity. It would be analogous to saying that one understands the concept of a triangle (i.e., three-sided figure, internal angles of 180 degrees) and then turn around and state that triangles are four-sided figures. For in Descartes’ view, if one understands the concept of a triangle, one understands it has three sides, and correspondingly, if one understands the concept of God, one understands that this entity possesses the property of existence.

However, the only connection that can be maintained from Descartes’ mountain and triangle analogies is that a property is inseparable from the concept, not from the existence of the concept itself (i.e., a valley is inseparable from the concept of a mountain, however, the simple concept of a mountain does not guarantee its existence). On such an account, Descartes believes that he can make the jump from the conception of God to instantiation of God by direct intuition. This is obviously cognitively suspect. Aware of the possible appearance of sophism, Descartes states:

…I can no more think of God as not existing than I can think of a mountain without a valley, nevertheless it surely does not follow from the fact that I think of a mountain without a valley that a mountain exists in the world. Likewise, from the fact that I think of God as existing, it does not seem to follow that God exists, for my thought imposes no necessity on things. (Descartes 5:44)

Yet, even with this acknowledgement, Descartes does not see this as a serious problem in continuing. For Descartes, it does not appear essential to have to establish that for every mountain there will be a valley - he only has to identify the fact that when we think of the concept of a mountain, the concept of its accompanying valley is explicit and incontrovertible. "But from the fact that I cannot think of God except as existing, it follows that existence is inseparable from God, and that for this reason he really exists." (Descartes 5:44) Thus, the ontological argument purports that the very concept of God is such that it necessitates instantiation of this entity. Although Descartes’ move from conception to reality continues to carry traces of sophism, the logical necessity of the proof is very persuasive. To affirm the concept of God, yet deny the existence of God would be a contradiction.

Two Proofs for the Existence of God?

Another problematic notion of Descartes’ project with respect to the argument for the existence of God is the fact that he felt the need to introduce two separate proofs for the existence of God — a causal proof in the third meditation and the ontological proof in the fifth meditation. One might think that two separate proofs would only strengthen Descartes’ argument, however, in reality it does not. Although the Mediations is a well-written, and tersely argued treatise, which includes numerous examples and analogies to algebra (i.e. the certainty associated with mathematical truths), it is suspicious that Descartes felt the need to include two separate arguments. It is the empiricist methods of observation and experimentation that Descartes rejects as error prone and limiting to the project of total and certain knowledge. Descartes believed that with the employment of a rational method of inquiry which applied some of the methods of analytic geometry to the study of philosophy, our ability to attain certainty and validity about our knowledge would be greatly increased. Yet, knowing that Descartes partially bases his deductive methodology on mathematics, it is surely questionable why he felt the need to have two distinct proofs. If we needed two separate proofs to show the validity of an algebraic equation, we would certainly be wary of its veracity. Once a theorem or proof has been established, there is no need to formulate subsequent conceptual proofs of the same entity or equation.

For Descartes to include a second and distinct proof for the existence of God, he must have believed that the causal argument was not strong enough, or may not have overwhelmingly convinced sceptical readers. In Descartes’ opening letter of dedication he states that "… although I believe these arguments to be certain and evident, still I am not thereby convinced that they are suited to everyone’s grasp." Although the inclusion of two proofs without explanation is methodologically sloppy, one must assume that Descartes believed that it was more important to prove the existence of God beyond a reasonable doubt.

Yet, one must also assume the Descartes was aware of the possible fault in resting the existence of God on the argument in the third meditation. The causal argument hinged on the a priori assumption that an effect cannot be greater than its cause. However, unlike the contradiction of affirming the concept of God (i.e. a single, perfect God) then denying God’s existence, it would not be contradictory to affirm the concept of God, yet maintain that there could be at least one case when the effect is indeed larger than the cause. If Descartes were to have only presented the causal proof for the existence of God, the internal coherence of this epistemology could be severely damaged or compromised if this relationship between cause and effects were to breakdown - especially since God plays the most important role in Descartes epistemic theory. By introducing the second proof for the existence of God, Descartes can avoid any possible self-contradiction in his earlier causal argument.

However, Descartes’ introduction of a second proof for the existence of God does not come away unscathed. There is another assumption explicit in the ontological proof - namely that existence is a positive property. There are many noted philosophers subsequent to Descartes, specifically David Hume and Immanuel Kant, who have challenged the notion that our conception of a perfect being must necessarily possess the property of existence. Since Descartes’ epistemic method renounces a posteriori knowledge in favour of particular a priori assumptions, when substantive objections to these assumptions are proffered (against these supposedly self-evident truths) it severely weakens the integrity of Descartes’ theory.

Although there are many problematic notions and strong objections to certain lines of argumentation and conclusions in the Meditations, Descartes believes that he has succeeded in this part of his project (namely providing incontrovertible proof for the existence of God). It was essential for Descartes to attempt to establish that we could be certain about the existence of God because without it, Descartes believes that we will never have the ability to possess certain knowledge. Without this proof, Descartes’ entire rationalistic epistemology would have failed. Through the examination of the role God plays in Descartes’ epistemic theory, it may be easier to understand why Descartes, a man who was a stickler for a rational process that avoided error, was willing to fudge on the methodological integrity of his work.

God and the Attainment of Knowledge

Although Descartes’ rational foundationalism moves away from Biblical revelation and Papal authority to a system of individually verifiable knowledge, God still plays an enormous role in Descartes epistemology. Not only does Descartes believe in the existence of God (and hope to convince the readers of the Meditations to come to the same conclusion), he believes that this new system of inquiry succeeds as a result of God’s existence. If we are to succeed in our project of attaining fundamental and certain knowledge, it will depend on the existence of a benevolent God who allows us to access this knowledge. Descartes would like to argue that God is so important to our acquisition of knowledge that even the certainty of geometrical demonstrations will depend upon the knowledge of God. "And thus I see plainly that the certainty and truth of every science depends exclusively upon the knowledge of the true God, to the extent that, prior to becoming aware of him, I was incapable of achieving perfect knowledge about anything else." (Descartes 5:47)

Descartes’ criticism of empiricism for its lack of certainty is solved by the role of God in his epistemic theory. It is our sense experience and propensity to error that stands in the way of the attainment of certain knowledge.

But once I perceived that there is a God, and also understood at the same time that everything else depends on him, and that he is not a deceiver, I then concluded that everything that I clearly and distinctly perceive is necessarily true. Hence even if I no longer attend to the reasons leading me to judge this to be true, so long as I merely recall that I did clearly and distinctly observe it, no counter-argument can be brought forward that might force me to doubt it. On the contrary, I have certain knowledge of it." (Descartes 5:46-47)

Thus, on Descartes’ account, with the employment of his rationalistic methodology and confidence of knowing that God indeed exists, we can now be sure that we will be able to inquire into and attain certain knowledge.

Descartes’ declaration that without God we will never have certain and true knowledge is a powerful assertion (at least emotionally). It is powerful because the role certainty and truth plays in our lives, and in turn the acquisition of knowledge, is tremendously important. I would submit that when we strive for the attainment of knowledge, we must hold the belief (even if it is in the back of our minds) that when we inquire about a subject or proposition, we aim at truth. We would not inquire into particular questions or hypotheses if we did not think that we could reach a true and accurate conclusion. More explicitly, it would not make sense to inquire into a subject if we believe that it would render false and/or unsustainable knowledge.

On Descartes’ account, it is precisely the certainty with which we now know that God exists that will allow us to know what a certain proposition or state of affairs must aspire to. With the establishment of fundamental truths (such as the existence of God), we will be able to build a system of knowledge on a robust and certain bedrock. And it is from this solid base that we will be able to add other certain truths to our system of knowledge. It is evident that Descartes had a desire to establish a body of certain knowledge (especially a body of knowledge dependant on the existence of God) that would not be corrupted or turned on its head as had been done by individuals such as Copernicus or Galileo. The existence of God in Descartes’ epistemology is necessary for stability and certitude in our lives. "Thus, other arguments can be brought forward that would easily make me change my opinion, were I ignorant of God. And thus I would never have true and certain knowledge about anything, but merely fickle and changeable opinions." (Descartes 5:46)

However, even if we were to let Descartes proceed with his two proofs for the existence of God and the role that God plays in our ability to gain certain knowledge, it does not guarantee unadulterated access to every tidbit of knowledge found in the world. On Descartes’ account, it is God who allows us to know "what is important to us." If certain chunks of knowledge are deemed by God to be too complicated or unnecessary to our understanding of the world, we will not have access to it. As such, there will be some metaphysical truths that will remain unknown and uncertain.

It appears evident that the establishment of a system of inquiry (which aims at acquiring true and certain knowledge) that limits itself to particular truths or states of affairs is tremendously problematic. At the beginning of our new rationalistic system that will allow us to finally be absolutely certain about the knowledge we may gain, why would we want to limit its scope? Although in the process of inquiry we may find that further argumentation, experimentation, or rationalization may fail to discover a certain truth about event or proposition X, to limit ourselves from the outset from trying to attain the truth about X appears to be self-defeating. Moreover, knowing how prone we, as human beings, are to error, should we not be cautious in the pronouncements of such limits. What if we are wrong in our belief that certain metaphysical truths are unknowable by God’s designation? We could be close to attaining additional certain knowledge, however, under Descartes scheme since we think certain truths are unknowable, we will not bother to inquire about them. Certain metaphysical truths or derived knowledge could be lost indeterminably. Therefore, if the goal of inquiry is indeed truth, why would we want to limit that inquiry? The downgrading or limiting of certain knowledge and truths in the world can easily lead us down the path of relativism.


Can anything from Descartes’ argument for the existence of God and the role God plays in the attainment of knowledge be salvaged? Unfortunately, I believe that there are too many problems with the internal coherence of Descartes’ epistemic theory to make it tenable. However, that does not mean that we cannot acknowledge the impetus behind Descartes’ project. Although Descartes fails to adequately prove the existence of God and our ability to gain certain knowledge based on that existence, Descartes did a great deal to advance to notion that with education and training in proper methods, individuals could inquire into the nature of the world and be confident that independent attainment of knowledge was possible — distinct from the authority of the Church or other authoritarian institutions.


Descartes, René. Meditations on First Philosophy — 3rd Edition. Donald A. Cress, translator. Hackett Publishing Company, Indianapolis, 1993.


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