Descartes on God

After carrying out his systematic doubt, and introducing the possibility of complete and constant deception, Descartes’ finds himself lost in a lonely solipsism, with only the indubitable knowledge that he exists, and that he is a thinking thing. He seeks a way to extricate himself, and to provide a new epistemic foundation to replace the scholastic tradition he inherited. The knowledge he has gained thus far does not seem to be able to help him; He decides that he must ‘examine whether there is a God’ as soon as possible, for without a God, he could not be sure of anything (Descartes, 1986, p. 25). Not satisfied with previous arguments for the existence of a supreme being, Descartes aimed at not only showing the ‘necessity’ of a divine being, but wanted to link this being with that of his Judeo-Christian religious traditions. He offers two primary arguments for Gods existence in his ‘Meditations on First Philosophy’; one in the Third Meditation, and one in the Fifth. Importantly, these ‘proofs’ are not extraneous to his undertaking, but are central to it; If these proofs fail, so too does a considerable portion of his project. Therefore, it is important to carefully examine these arguments and highlight any problems with the proof, and how these might be answered. The causal argument of the Third Meditation and the ontological argument of the Fifth Meditation will be standardised and analysed to determine if these proofs succeed. However, In order for readers to follow his reasoning, and to aid in a charitable examination, a necessarily brief and tailored introduction to Descartes’ theory of ideas will be presented.

Firstly, since Descartes’ is currently only certain that he is a ‘thinking thing’; the next most logical step for him is to look at his thoughts (Williams, 1978, p. 116). He introduces a category of his thought as ‘ideas’, which are ‘images of things’ (Descartes, 1986, p. 25). Descartes does not mean to imply that ideas must be a pictorial image, so a less ambiguous meaning might be ‘representations of objects’ (Beyssade, 1992, p. 179). He further informs that these ideas, ‘considered solely in themselves’ without being referred to anything, cannot be false (Descartes, 1986, p. 25). However, he needs to discover where these ideas came from.

Descartes’ provides three mutually exclusive options; ideas can ‘innate’, wholly from within; ‘adventitious’, provided from sensory experiences; or ‘invented’ by the imagination (Descartes, 1986). At this stage, Descartes’ does not know which ideas fall into these categories, because he has been deceived before, so to use this understanding, he must investigate whether any ideas actually resemble their objects. When considering his ideas as ‘modes of thought’, they are equal; they cannot be distinguished by their source, or their degree of reality. However, when looking at what his ideas represented, order began to present itself; His ideas ‘formal reality’ may not differ from one another, however it was clear to him that their content modified the ideas ‘objective reality’ (Descartes, 1986). Based on this, he claims that substances ‘amount to […] more’ and so must contain more ‘objective reality’ than that of modes and accidents (Descartes, 1986, p. 28).

This notion of things having different degrees of reality is important for Descartes’ argument. He wants to invoke the ‘scholastic distinction’ of formal, eminent and objective reality. For Descartes, substances have the quality of independent existence (Williams, 1978, p. 121), and so have ‘formal’ reality intrinsic to their nature. Likewise, an idea of a substance has ‘formal’ reality as a ‘mode of thought’, however also has ‘objective’ reality based on the substance it represents.

Using the foundations he has set, he looks at his various ideas, to determine if there are any ideas within him that could not have been produced by him. He considers various substances, and finds that he could have produced all of these, except for one: his idea of God. This idea, of a God who is ‘eternal, infinite, <immutable,> omniscient, omnipotent and the creator of all things that exist apart from him’ (Descartes, 1986) has significantly more objective reality than ideas of other substances.

With an understanding of these general principles, the examination of Descartes’ arguments for the existence of God begins in earnest. In the pages to follow, the two arguments will be outlined, along with an examination of the problems and possible solutions which arise. Finally, the arguments will be evaluated on their strength.


Axiom 1: A cause provides the effect with its reality – ‘[T]here must be at least as much <reality> in the efficient and total cause as in the effect of that cause’ (Descartes, 1986).

Axiom 2: ‘Something cannot arise from nothing’, ergo, everything must have a cause.

Axiom 3: My ideas must have a cause [from A2],

Axiom 4: ‘for a given idea to contain such and such objective reality, it must surely derive it from some cause which contains at least as much formal reality as there is objective reality in the idea [from A1 & A2]

Axiom 5: Infinite regresses are not possible, both formally and objectively; ‘eventually one must reach a primary idea which will be an archetype which contains formally <and in fact> all the reality <or perfection> which is present only objectively <or representatively> in the idea’ (Descartes, 1986, p. 29).

Axiom 6: The ‘more perfect […] cannot arise from what is less perfect’ (Descartes, 1986, p. 29).

  1. IF “the objective reality of any of my ideas turns out to be so great that I am sure the same reality does not reside in me, either formally or eminently, and hence that I myself cannot be its cause” THEN “I am not alone in the world, but that some other thing which is the cause of this idea also exists.” (Descartes, 1986, p. 29)
  2. I could not possibly have been the cause of my idea of God [from 2.1, 2.2 & 2.3]
    1. I have an idea which contains an infinite amount of objective reality
      1. I have an idea of God who is ‘eternal, infinite, <immutable,> omniscient, omnipotent and the creator of all things that exist apart from him’ (Descartes, 1986, p. 29).
      2. In order to have this idea, I must have an innate idea of perfection
        1. ‘I clearly understand that there is more reality in an infinite substance than in a finite one, and hence that my perception of the infinite […] is in some way prior to my perception of the finite’ (Descartes, 1986, p. 31)
      3. Ideas in me may fall short of reality, but cannot contain more perfection
    2. I am imperfect
      1. I myself am a finite being.
        1. Finite beings have finite formal reality
  3. [from P1 & P2] ‘I am not alone in the world, something other than me must exist’ to have caused my idea of God

– – –

  1. [from A1 – A6] Only a being with infinite formal reality could be the cause of an idea with infinite objective reality.
  2. Therefore, God exists [from 3 & 4]


The proof presupposes a similarity in the cause and its effect, leading Descartes to claim the idea of God was innate within him ‘like the mark of a craftsman’ (Descartes, 1986, p. 35). However, the rationalist conception of ‘innate ideas’ has been challenged by various thinkers, including Locke and Hume (Hume, 1978; Locke, 1690). Ideas of God and religious notions are heavily dependent on cultural factors, demonstrated by the quantity of different religions around the world, and across the ages. Similarly, there are individuals and cultures that have not been brought up to believe in God, who do not naturally come to the conclusion that there is a being like Descartes describes without having ‘instruction’ in a religion. If the idea of God were truly innate, based on Descartes’ own argument, it would be expected that all people would have highly similar, if not identical, conceptions of God; this was a point highlighted in Descartes day by Gassendi. The idea of God could perhaps have simply been transmitted through social contact.

Descartes’ has a response to this. In the Objections and Replies, Descartes’ responds to several queries regarding the denial of an ‘idea’ of God. Descartes’ most comprehensive response is in the Second Replies, informing that those who deny they have an idea of God are not truly denying the absence of this idea but instead simply rejecting the name given, and claiming they don’t have an ‘image’ of God (Descartes, 1642, p. 24). He appears to think that the denial of the idea is only related to the inability to visualise God, rather than denying the ideas contents. Related to this is his response to Gassendi, where Descartes’ implies that it should not be surprising that people draw varying conclusions about their idea of God, because they may be attending to different points, or making false judgements (Descartes, 1642, p. 120). These responses do not seem to be satisfying, because if this idea were truly innate and provided by God, it seems reasonable to think there would be a greater perfection in the ‘mark’ and so leave less capacity for denial. It also leaves the question open as to how certain cultures are completely ignorant, and must be instructed in the knowledge of God.

Another possible flaw in this argument is in Descartes’ axiomatic assumption of causation. Hume argued that the notion of causation was not ‘intuitively nor demonstratively certain’, but instead relied upon ‘observation and experience’ (Hume, 1978, p. 82). Hume considers that even a posteriori causation cannot be proven with certainty, particularly in the case of first causes; there is no way to gain experience of these, and so assumptions are made based on current experience, and extrapolated to other experiences inductively (Hume, 1978). It therefore seems reasonable to ask, at the point of the third meditation, why this premise should be granted. Since we have not yet accepted the proposition ‘God exists’ in order to defeat the possibility of deception by the Evil Demon presented earlier in the Meditations, nor have we been given proof of the external world in which we could (presumably) establish this a posteriori, this axiom should be challenged.

After giving this highly complex ‘proof’, Descartes considers the reader to be ready for a simpler proof. This is the Ontological proof of the Fifth Meditation, which aims to prove Gods existence by an appeal to the ‘essence’, or ‘nature’ of God. This ‘essence’ is identified through the definition of ‘God’ as he appears to Descartes consistently across the Meditations.


Axiom 1: All things have an essence; that which defines them.

Axiom 2: ‘Even though there may not be anything outside of me, my ideas of things cannot be called nothing’ (Descartes, 1986).

  1. It is in Gods’ nature to have every perfection
    1. I have a clear and distinct idea of God ‘within me, as surely as any number’ (Descartes, 1986)
      1. Even if nothing else is true, God has the same level of certainty as any attribute of mathematics
    1. Existence is one of the perfections God has (i.e. It is more perfect to exist).
      1. ‘Existence can no more be separated from the essence of God than the fact that its three angles equal two right angles can be separated from the essence of a triangle’ (Descartes, 1986, p. 46)
      2. I cannot think of God except as existing
    2. God exists


One particular theme in the objections to this argument was the criticism that Descartes assumes that existence is a property. These objections were even made in Descartes time, with objectors claiming this argument could fall prey to proving the existence of anything (Descartes, 1642, pp. 14,31,32,52,129,132,156,157). Descartes appears to be making a considerable leap from a definition of a concept, to existence in the actual world. With this format argument, we could argue for the existence of just about anything. Mackie (1982, p. 43) illustrates this with the example of a ‘Remartian’; not just an idea of an alien from Mars, but a ‘Real’ Martian. This ‘Remartian’ would have all the qualities of a standard Martian, but with ‘existence’ built into the concept; it would become part of the essence of the ‘Remartian’. It seems that Descartes reasoning would have us accept the existence of these beings. With the assistance of Immanuel Kant, the issue was able to be articulated. Kant tells us existence is ‘obviously not a real predicate’ because ascribing existence to an object does not add or take away from it (Kant, 1999, p. 200 A599/B627). Existence is the requirement before an object can have any properties outside of their concept (Descartes, 1642, p. 132).

However, Descartes can respond to this charge; in the First and Second Replies, he appears to acknowledge this difficulty with his proof. While the existence of ‘Remartians’, or other mythological creatures may be posited, none of these have ‘necessary existence’, but only ‘possible existence’. This is not the kind of existence which must be attributed to God. In a clarification to the argument in the First Replies, Descartes claims:

  1. What he clearly and distinctly understands of the true essence of something can be asserted
  2. When we know what God is, we ‘clearly and distinctly’ realise existence belongs to this nature
  3. Therefore, God exists    (Descartes, 1642, p. 13)

The conjoining of all perfections in God makes existence a necessary feature in, and only in, the case of God (Descartes, 1642, pp. 16,132). The ‘true and immutable nature’ of God is such that he cannot be imagined without existence, unlike the contingent natures of other beings. Denying the existence of God would be a contradiction, because this being would lack total perfection.

This however, is unconvincing. There appears to be a degree of support from the arguments in Meditation Three being assumed. If we have accepted the existence of God from those arguments, then it could be granted that there is a specific implied premise here, in that without God nothing could exist; while this arguably may affect Kant’s argument, this then becomes an article of faith, since without the support from the earlier arguments, then it is unlikely that someone would grant this without further argumentation.


Descartes offers two primary ‘proofs’ for the existence of God. Both of these arguments are emotionally powerful for theists, and serve to provide justification for their belief. However, they face significant challenges to their conclusions. While there is some measure of mitigation with these difficulties, it is clear overall that these arguments do not succeed in ‘proving’ the existence of any deity.


Beyssade, J.-M. (1992) ‘The idea of God and the proofs of his existence’ in J. Cottingham, (ed.) The Cambridge Companion to Descartes,
Cambridge: Cambridge University Press.

Descartes, R. (1642) ‘Objections to the Meditations and Descartes’s Replies’ in Meditations on First Philosophy,
[online], available:

Descartes, R. (1986) Meditations on First Philosophy: With Selections from the Objections and Replies, Cambridge:
Cambridge University Press.

Garber, D. (2003) ‘Descartes, Rene’ in E. Craig, (ed.) Routledge Encyclopedia of Philosophy,
Routledge, [online], available:

Hume, D. (1978) A Treatise of Human Nature, Oxford:
Oxford University Press.

Kant, I. (1999) Critique of pure reason (abridged), Indianapolis:
Hackett Pub.

Locke, J. (1690) ‘Book I: Innate Notions’ in An Essay Concerning Human Understanding,
[online], available:

Mackie, J. L. (1982) The Miracle of Theism: Arguments for and against the Existence of God, Oxford:
Oxford University Press.

Nadler, S. (2006) ‘The Doctrine of Ideas’ in S. Gaukroger, (ed.) The Blackwell guide to Descartes’ meditations,
Oxford: Blackwell Publishing.

Nolan, L. & Nelson, A. (2006) ‘Proofs for the Existence of God’ in S. Gaukroger, (ed.) The Blackwell guide to Descartes’ meditations,
Oxford: Blackwell Publishing.

Williams, B. (1978) Descartes: The Project of Pure Enquiry, Harmondsworth:

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