Anselm's Argument For The Existence Of God

Descartes would agree with Anselm’s conclusion that God exists but he would likely attack Anselm’s method of reaching this conclusion with the Fool. The arguments share a major commonality in their reliance upon the human mind in proving God’s existence. In both arguments, God’s existence becomes evident when reflecting on an idea of God. In both cases, possessing an idea of God is enough to prove God’s existence. These similarities, however, are not be enough to protect Anselm from Descartes’ hypothetical criticism of the method by which Anselm gets the Fool to admit that God exists. Descartes’ would take issue with the role that the mind plays in Anselm’s argument. In Descartes’ argument, the mind plays a necessarily passive role in understanding

God; on the other hand, Anselm’s argument requires that the mind play an active role in the understanding of God. This one difference is so fundamental to both Descartes’ and Anselm’s arguments that it would likely cause Descartes to reject Anselm’s argument even if he agreed with Anselm’s final conclusion that God exists.
For Descartes’ argument to work, the mind must not be able to conceptualize God on it’s own. The very fact that we are able to possess an idea of God points to his existence, because our mind cannot generate such ideas independently according to Descartes’ characterization of ideas as caused by perception. The idea of God must ultimately be sourced from something real which acts as it’s cause. After eliminating worldly objects as possible sources of the idea of God, Descartes concludes that the source of our idea of God must be none other than God himself. Here, the mind takes a passive role in the understanding of God in that it receives the idea from the external world rather than generating the idea using concepts already internal to the mind.
For Anselm’s argument to work, the mind must be able to do it’s own work in generating an understanding of God based solely off a concept of “that than which nothing greater can be thought.” Anselm basically gets the Fool to build up to the idea of God (then eventually God’s existence) from this phrase alone.

Importantly, the Fool must be able to understand the idea of “that than which nothing greater can be thought” without yet conceding that God exists. By contemplating the phrase “that than which nothing greater can be thought,” the Fool generates an idea of God that ultimately requires him to accept that God exists. To be clear, Anselm is not arguing that God depends upon the Fool’s ideas, but rather that the way in which we go about conceiving of God as “that than which nothing greater can be thought” reveals that He must exist. In an analogous conceptual process, we understand that circles are necessarily round after learning the definition of a circle. Likewise, we understand that God exists after learning what constitutes “that than which nothing greater can be thought.” In this way, the mind plays an active role in this argument because it is the tool by which one can reveal the necessity of God’s

existence.
Because Descartes takes on a view of the mind as a passive recipient of the idea of God, he would not concede that the Fool could conclude that God exists merely by understanding “that than which nothing greater can be thought.” Descartes would claim that the Fool could only understand God as “that than which nothing greater can be thought” if God had already caused the Fool to have an understanding of the concept of infinity (which is integral to the Fool’s conception “nothing greater”). In this case, it would be the fact that the Fool could conceptualize God at all that is proof for God’s existence. This would be far enough in the argument for Descartes to conclude God must exist. He would see no need to go on with the semantic implications of Anselm’s definition of God as “that than which nothing greater can be thought.”