Thursday, April 7, 2011

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.

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

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