Happy birthday, David Hume

The most perfect philosophy of the natural kind only staves off our ignorance a little longer: as perhaps the most perfect philosophy of the moral or metaphysical kind serves only to discover larger portions of it. Thus the observation of human blindness and weakness is the result of all philosophy, and meets us at every turn, in spite of our endeavours to elude or avoid it.

From An Enquiry Concerning Human Understanding

What's wrong with the Ontological Argument?

The Ontological Argument is a strange little argument that rears its head periodically in the history of philosophy.

One traditional version goes like this:

P1. God is the maximally perfect being (possesses every perfection).
P2. Existence is a perfection
C. Therefore, God exists

Descartes' version of the Ontological Argument

For Descartes, anything that is perceived clearly and distinctly must be true. Therefore, when we know the essence of some idea, we have a clear and distinct idea of what that idea necessarily contains. In this ability to see as true or real any idea of a property contained in the essence of an idea Descartes sees another avenue for the demonstration of God’s existence.He claims to see clearly and distinctly that it is in the nature of God that he always exists. It is clear, he says, when he pays careful attention to the idea of God that God’s existence cannot be separated from his essence, any more than having three angles is separable from the idea of a triangle (CSM II 45-6). With this simple argument Descartes takes himself to have demonstrated the necessary existence of God.

Descartes anticipates an obvious objection: the fact that a property is part of the essence of an idea and cannot be separated from it doesn’t mean that entity that the idea represents actually exists.  Descartes responds that because the property in question contained in the essence of God is his existence, it does in fact entail his real existence.  It is not the thought or the definition that makes God necessary, rather it is his necessary existence that produces the necessity we clearly perceive in the idea of God. Descartes claims we are simply not free to think of God as not existing, for this would be to think of a supremely perfect being without a perfection (CSM II 46). He adds (without argument) that it is only in the case of God that existence is contained in the essence, so this argument could not be used to demonstrate the existence of anything else (CSM II 47).

One problem with this is the so-called "Cartesian Circle" in which Descartes may have employed a vicious circle in his defense of the veracity of clear and distinct ideas. According to some interpreters, Descartes needed the existence of God to provide the foundation for the reliability of clear and distinct ideas, which he then employed in his proof of the existence of God. Thus a vicious circle. This interpretation is contested, however (see here for more details). But even if we set that problem aside as unresolved there are major problems with this argument.

The notion that existence is a property contained in the essence of the idea of God is problematic. If Descartes means existence is a necessary condition (as part of a set of necessary and sufficient conditions) of being God, then the claim is uncontroversial but extremely uninformative. Also, the idea of God doesn't contain existence in any special way on this construal. In this sense existence is also a necessary condition of being a hammer (i.e., if something does not exist, then it isn't a hammer). But we can't infer anything at all about whether there actually are any hammers on the basis of this definition.

Alternatively Descartes could mean that there is a real metaphysical entity that is God's actual essence (like a Platonic form, perhaps), of which existence is a property in a way that existence is not a property of other real essences. Setting aside the profligate multiplication of entities this sort of metaphysics requires, Descartes gives us no reason for thinking that the essence of God is necessarily unique in this regard. Rather he repeatedly simply asserts that it is only the essence of the idea of God that has this necessary connection to existence; all other existences are contingent.

Ultimately, I think the only way to construe Descartes' argument without attributing a non sequitor to him is to read it as an argument for the psychological certainty that God exists. Unfortunately for Descartes, this means that he proves much less than he intended. The psychological version would go roughly like this:

1. We are psychologically unable to doubt the veracity of clear and distinct ideas 
2. We see clearly and distinctly that the essence of the idea of God contains existence as a property
3. We are unable to doubt that God's existence is entailed by the idea of God
4. We unable to doubt God exists

Of course, this argument merely points at a failure of human imagination rather than entailing anything at all about the existence or nonexistence of God.

Descartes' Argument from Personal Existence

Is it possible for me to exist if God does not? For Descartes, given that our existence is indubitable (I think, therefore I am), a negative answer to this question would serve as a demonstration that God's existence follows as a logical certainty from the indubitable proposition that I exist. In the Third Meditation Descartes seeks to establish the existence of God through just such an argument. He places the existence of God among three possible alternative causes for his existence: himself, his parents, or some other confluence of causes less perfect than God (CSM II 32-3).

Descartes surveys the other possible sources of his existence, dismissing each in turn.

First, if it were possible for him to bring himself into existence, then he should have given himself all the perfections he lacks, which would make him God. If he possessed the power of self-creation then he would possess enough power to give himself all other perfections. In addition, the power to create is the same as the power to sustain existence. Therefore, if he were self-created, then he would be responsible for maintaining his own existence. He does not do so, so he must not have been responsible for his own creation (CSM II 33-4). The key component of this portion of the argument is that Descartes is asserting that the power to create something is the same as the power to sustain the existence of something. There seems to be no reason to think that creative acts and sustaining acts--even those by God--are necessarily connected in the way Descartes supposes. Now, it seems fairly clear that I am not the source of my own being, even without Descartes' argument, but Descartes will deploy this notion of the equivalence of sustaining and creating later on in the argument.

Second, his parents cannot be considered to be the source of his being; they do not sustain him, and so insofar as he is a thinking thing, they did not make him, even if there is a sense in which they can be considered to be the source of his being in the world (CSM II 35). The dismissal of his parents as a legitimate explanation for his existence is based on the equivalence of creating and sustaining just mentioned as well as on Descartes' conception of the soul as thinking substance being somehow independent of the physical body. Descartes could accept a limited sense in which his parents brought him as a physical being into existence, but not that they are in any way responsible for the "thinking thing" that he identifies with himself. Cartesian dualism is implicit here, even though Descartes does not attempt to prove the thesis until later on in the Meditations.

Third, he cannot be the effect of a composition of causes because then he would have no source for the idea of God; the idea of God is a unity, and so cannot be a composite of other ideas (CSM II 34). This argument depends on Descartes' argument from conceptual content which I have discussed (and found wanting) previously.

Having dismissed three of the four alternatives in his quadrilemma, Descartes feels justified in taking this line of thought to have demonstrated the existence of God. Whether his argument really accomplishes what he thought it did is, as we've seen, debatable at best. 

What is perhaps more interesting in all this is that Descartes felt that the fact of human existence was so mysterious a feature of the world that it required a special causal story to be told. If we reject dualism, then there is no reason to require any special explanation. If the mind is simply the loose moniker we give to the different capacities we have as the result of having big brains (rather than some extra thing that supervenes on the physical or is mysteriously associated with it somehow) then Descartes' problem dissolves to a large extent.

Human existence (including the existence of human intelligence) is a contingent fact about the world that is the result of a probably innumerable confluence of causes, any combination of which can be picked out depending on which aspect of human existence we find interesting. Answers to the question "why are we here?" could be explanations about what makes the universe in general or the earth in particular hospitable to life or about genetics and developmental biology or about human evolution or about human history or.... 

You get the point. There isn't any one answer for "why we're here," and Descartes' need to have one answer is derived from his insistence that there is something unnatural about our ability to think.


References:
Cottingham, J. G., Stoothoff, R., and Murdoch, D. (eds), The Philosophical Writings of Descartes, 2 vols. Cambridge University Press, 1985