I will exposit Descartes reply to an objection against his argument for the existence of God. Then I will give reasons why I think Descartes successfully answers the objection.
First, Descartes states the fact that God’s essence necessitates his existence looks suspicious. He says, “Since in all other matters I have become accustomed to distinguishing existence from essence, I easily convince myself that it can even be separated from God’s essence and, hence, that God can be thought of as not existing.” Here, Descartes makes the point that we can in thought separate the essence of something from its existence. In the case of God, it seems one can think of God’s essence without His existence. The concept of God can be thought of without demanding the concept to have actual existence. But Descartes believes that when we examine further into God’s essence we come to understand it is inseparable from His existence. As Descartes explains, “But nevertheless, it is obvious to anyone who pays close attention that existence can no more be separated from God’s essence than 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.” By this Descartes reasons, it is contradictory to think of God, the supremely perfect being (i.e. one without lack), as lacking actual existence.
Descartes argues further that people cannot think of God apart from existence, much like a mountain cannot rightly be thought of without a valley. However, he admits the fact that although people cannot think of God apart from existence, it does not necessitate his existence. As Descartes says, “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. And just as one may imagine a winged horse without there being a horse that has wings, in the same way perhaps I can attach existence to God, even though no God exists.” Clearly, Descartes is saying that God can be thought of as having existence, like a horse with wings, and yet not in fact exist. Hence, God can be thought of as an idea with existence without having actual existence.
However, Descartes says to easily the inseparability between God’s essence and his existence is excused. Certainly, a person cannot think of a mountain apart from a valley, then reason that a mountain or a valley must exist somewhere; nevertheless, it proves that a mountain and valley are inseparable from each other. Likewise, God cannot be thought of apart from existence; and since existence is inseparable from God, he must exist. As Descartes puts it,
“Likewise, 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. Not that my thought brings this about or imposes any necessity on anything; but rather the necessity of the thing itself, namely, of the existence of God, forces me to think this. For I am not free to think of God without existence, that is, a supremely perfect being without a supreme perfection, as I am to imagine a horse with or without wings.”
By this Descartes says that thought does not make God exist by necessity; rather it is the concept of God itself that forces one to concede God exists. For it is impossible to think of God without existence. This is in virtue of the fact that God is the supremely perfect being, and this necessitates he possess actual existence. Hence, God must exist.
In my judgment, Descartes reply sufficiently answers the objection. For I see no reason to think the concept of God cannot entail His actual existence. I do concede however the objection shows that concepts, like God, can exist in the mind and/or in reality. And the objection Descartes articulates points to the fact that concepts can contain existence as a description, and yet not exist. However, in the case of God, I think Descartes clearly demonstrates that the concept of God necessitates his actual existence. Descartes speaks of the essence of a triangle having three angles is inseparable from being equal to two right angles. This example illustrates that it is essential for a triangle to possess three angles, which is inseparable from being equal to two right angles in order to be a triangle. Thus certain characteristics define the concept of a triangle. If a thing is to be a triangle, it must have certain characteristics. Likewise, Descartes shows that God must possess actual existence in order to fit the concept of God. This is because actual existence is inseparable from the concept of God. Now the objection would state that the concept of God does not have existence in reality, but only in minds. But as Descartes rightly points out, one essential characteristic to the concept of God is existence in reality, and not only in minds. This is in virtue of the fact that God is by definition the supremely perfect being without any lack or need. And as such, he must possess actual existence. So we may conclude God must exist. By this reply, I think Descartes answers the objection. But still, some would object to Descartes on the basis that one could not define something, like God into existence. The property of actual existence added to the definition of God does not make him exist. The description of God may contain actual existence, but this fact alone does not ground his existence. Yet, I would say this is the same objection repackaged that Descartes deals with. Thus, it too fails to properly understand the concept of God. For if it did, then it would acknowledge the necessity for God to exist not only in minds, but also in reality. Nevertheless, I think the objection could be addressed in another way. Descriptions and concepts of things must ground their existence in something. In other words, descriptions and concepts must have existence in themselves or something else. The objection to Descartes’ argument assumes concepts come from humans, so the concept of God is a human construct with no existence outside the minds of men. But if this were the case, there would be a more perfect concept of God than the human created one, namely God’s original concept of himself grounded in his actual existence. Therefore, God must exist.
Descartes, Rene. Meditations, Objections, and Replies. Ed. Trans. Roger Ariew and Donald Cress. Indianapolis: Hackett, 2006. 36-37.
Kreeft, Peter and Ronald K. Tacelli. Handbook of Christian Apologetics. Downers Grove: Intervarsity P, 1994. 69-72.
Morland, J.P. and William Lane Craig. Philosophical Foundations For A Christian Worldview. Downers Grove: Intervarsity P, 2003. 496-499.
The Ontological Argument: From St. Anselm To Contemporary Philosophers. Ed. Alvin Plantinga. Garden City: Doubleday, 1965. ix-xiii.