The Arguments of the Proslogion

The arguments of the Proslogion

Looking back on the sixty-five chapters of complicated argument in the Monologion, Anselm found himself wishing for a simpler way to establish all the conclusions he wanted to prove. As he tells us in the preface to the Proslogion, he wanted to find

a single argument that needed nothing but itself alone for proof, that would by itself be enough to show that God really exists; that he is the supreme good, who depends on nothing else, but on whom all things depend for their being and for their well-being; and whatever we believe about the divine nature. (P, preface)

That "single argument" is the one that appears in chapter 2 of the Proslogion. (We owe the curiously unhelpful name "ontological argument" to Kant. The medievals simply called it "that argument of Anselm's" [argumentum Anselmi].)

The argument goes like this. God is "that than which nothing greater can be thought"; in other words, he is a being so great, so full of metaphysical oomph, that one cannot so much as conceive of a being who would be greater than God. The Psalmist, however, tells us that "The fool has said in his heart, 'There is no God' " (Psalm 14:1; 53:1). Is it possible to convince the fool that he is wrong? It is. All we need is the definition of God as "that than which nothing greater can be thought." The fool does at least understand that definition. But whatever is understood exists in the understanding, just as the plan of a painting he has yet to execute already exists in the understanding of the painter. So that than which nothing greater can be thought exists in the understanding. But if it exists in the understanding, it must also exist in reality. For it is greater to exist in reality than to exist merely in the understanding. Therefore, if that than which nothing greater can be thought existed only in the understanding, it would be possible to think of something greater than it (namely, that same being existing in reality as well). It follows, then, that if that than which nothing greater can be thought existed only in the understanding, it would not be that than which nothing greater can be thought; and that, obviously, is a contradiction. So that than which nothing greater can be thought must exist in reality, not merely in the understanding.

Versions of this argument have been defended and criticized by a succession of philosophers from Anselm's time through the present day (see ontological arguments). Our concern here is with Anselm's own version, the criticism he encountered, and his response to that criticism. A monk named Gaunilo wrote a "Reply on Behalf of the Fool," contending that Anselm's argument gave the Psalmist's fool no good reason at all to believe that that than which nothing greater can be thought exists in reality. Gaunilo's most famous objection is an argument intended to be exactly parallel to Anselm's that generates an obviously absurd conclusion. Gaunilo proposes that instead of "that than which nothing greater can be thought"