René Descartes’ Ontological Arguments and Objections

René Descartes (1596-1650) was a philosopher and mathematician arguably best known today for methodological doubt expressed in the famous dictum “Cogito, ergo sum” and mind-body dualism. In his Meditations on First Philosophy (1641), Descartes offers two versions of the ontological argument for the existence of God. His first version is as follows,

“Now if it follows, from my mere ability to elicit the idea of some object from my consciousness (cogitatione), that all the properties that I clearly and distinctly perceive the object to have really belong to it; could not this give rise to an argument by which the existence of God might be proved? I assuredly find in myself the idea of God – of a supremely perfect being – no less than the idea of a figure or a number; and I clearly and distinctly understand that everlasting existence belongs to his nature, no less than I can see that what I prove of some figure, or number, belongs to the nature of that figure, or number. So, even if my meditations on previous days were not entirely true, yet I ought to hold the existence of God with at least the same degree of certainty as I have so far held mathematical truths” (1).

Descartes’ argument can be presented as follows (2):

1. If I clearly and distinctly perceive some property to pertain to the nature of an object, then that property pertains to the nature of the object;

2. I clearly and distinctly perceive eternal existence to pertain to God’s nature;

3. Therefore, eternal existence pertains to God’s nature;

4. Therefore, God exists eternally.

According to this argument, the existence of God is a self-evident truth. In the same manner that one can immediately grasp mathematical axioms, he can also immediately grasp the nature of God as an eternal existence.

Descartes’ second version of the ontological argument is presented in the following,

“[T]here is indeed no necessity for me ever to happen upon any thought of (cogitationem de) God; but whenever I choose to think of (cogitare de) the First and Supreme Being, and as it were bring out the idea of him from the treasury of my mind, I must necessarily ascribe to him all perfections, even if I do not at the moment enumerate them all, or attend to each. This necessity clearly ensures that, when later on I observe that existence is a perfection, I am justified in concluding that the First and Supreme Being exists. In the same way, it is not necessary that I should ever imagine any triangle; but whenever I choose to consider a rectilinear figure that has just three angles, I must ascribe to it properties from which it is rightly inferred that its three angles are not greater than two right angles; even if I do not notice this at the time. When, on the other hand, I examine what figure can be inscribed in circles, it is in no way necessary for me to think all quadrilaterals belong to this class; indeed, I cannot even imagine this, so long as I will admit only what I clearly and distinctly understand. Thus there is a great difference between such false suppositions and my genuine innate ideas, among which the first and chief is my idea of God. In many ways, I can see that this idea is no fiction depending on my way of thinking (cogitatione), but an image of a real and immutable nature. First, I can frame no other concept of anything to whose essence existence belongs, except God alone; again, I cannot conceive of two or more such Gods; and given that one God exists, I clearly see that necessarily he has existed from all eternity, and will exist to all eternity; and I perceive many other Divine attributes, which I can in no wise diminish or alter” (3).

This version can be summarized as follows (4):

1. When I think of God I am necessitated to ascribe all perfections to Him;

2. Existence is a perfection; thus I am necessitated to ascribe existence to God;

3. Therefore, God exists.

There are several relevant considerations regarding both Descartes’ forms and Anselm’s version of the ontological argument. First, unlike Anselm’s version, Descartes’ does not appeal to the definition of God as that-which-no-greater-can-be-conceived. Descartes’s first version derives the existence of God directly from our clear and distinct idea of God’s nature, and the second version derives it indirectly from God’s perfection. Further, both Descartes’ and Anselm’s arguments attempt to prove the existence of God based on a priori reasoning alone.


One objection raised is that Descartes’ ontological arguments are question-begging in that the conclusion is already included in the premises (5). The nineteenth-century philosopher Arthur Schopenhauer (1788-1860) made this charge comparing the argument to a magic trick and dismissing it as a charming joke. Schopenhauer alleged that both Anselm and Descartes smuggle the conclusion that God exists into the premises of the argument,

“According to the objection in question, the ontological argument commits the fallacy because the definition of God as that-than-which-no-greater-can-be-thought, or as a supremely perfect being, implicitly presupposes that God exists. It is not surprising at all, therefore, that the argument can ‘derive’ the existence of God from the premises” (6).

But it is not clear that Descartes’ or Anselm’s ontological arguments are question-begging. According to Anselm, that-than which-no-greater-can-be-conceived must exist because if it does not then we can think of a being that is greater, which is logically impossible. Here God is not defined in a question-begging manner,

“Anselm does not derive God’s existence simply by presupposing that He exists. Descartes’s first version of the ontological argument does not seem vulnerable to this objection either. That version says, again, that the existence of God is a self-evident truth, which is comparable to mathematical axioms. If it is indeed true that the existence of God is comparable to mathematical axioms, then it is no more question-begging than mathematical axioms. It is in fact trivially true that the first version is not vulnerable to the objection in question because that version is not really an argument; it is just an expression of what Descartes regards as a self-evident truth” (7).

A further objection raised comes from the eighteenth-century German philosopher Immanuel Kant (1724-1804) who argued that existence is not a predicate (8). According to Kant, the ontological argument is unsuccessful because it is based on a mistaken assumption, which is that existence is a predicate. 

Predicates are words that refer to properties of things. For example, consider the statement “John is short”. The phrase “is short” is a predicate because it refers to John’s property of being short. The same would apply to other references. According to Kant, the ontological argument treats existence as a predicate by construing the statement “God exists” as “God has the property of being existent”. God, as that-than-which-no-greater-can-be-conceived has such a property because, the argument appears to assume, it is one of many great-making properties, properties that contribute to the greatness of God.

But Kant counters that the phrase “is existent” is not comparable to a normal predicate such as “is short”. When we express that John has the property of being short, we do not need to say, “John has the property of being tall and he exists” because the possession of a property entails the existence of the possessor. Conversely, it does not make sense to say that “John is short but he does not exist”. These observations show that existence is not a predicate or a property. Therefore, Kant concluded, the ontological argument fails.


1. Quoted by Stewart, David. 2017. Exploring the Philosophy of Religion. Oxfordshire: Routledge. p. 129.

2. Nagasawa, Yujin. 2011. The Existence of God: A Philosophical Introduction. Taylor & Francis Group. p. 16.

3. Quoted by Stewart, David. 2017. Ibid. p. 130

4. Nagasawa, Yujin. 2011. Ibid. p. 17.

5. Nagasawa, Yujin. 2011. Ibid. p. 25-28.

6. Nagasawa, Yujin. 2011. Ibid. p. 26.

7. Nagasawa, Yujin. 2011. Ibid. p. 26-27.

8. Nagasawa, Yujin. 2011. Ibid. p. 22-25.


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