Explain two versions of the ontological argument for the existence of God

     As the definition states God must be perfect, and existence is a perfection which an entirely perfect entity must possess, then God must have the perfection of existence. In other words, God must exist in re (in reality) not just in the mind (in intellectu) or else he would not be perfect.

In Anselm's second form of his argument he argues that God not only exists but he is a necessary being (self-causing) and by extension cannot not exist. He makes the point that if God existed in intellectu alone as a contingent being, then we could conceive of a necessary being which by extension would be more perfect than God. This would be contrary to Anselm's definition of God as a being that which nothing greater could be conceived so therefore God must exist necessarily or without cause. As a necessary being God must exist in re.

In Descartes' ontological argument he approaches the question slightly differently from the perspective of innate (something that exists inherently) ideas. He talks of how we perceive God as a supremely perfect being. As with Anselm this means that God is without flaws and has 'all the perfections'. He then goes on to posit that necessary existence is a perfection thus the logical progression is that a supremely perfect being has to exist or else it would lack the perfection of necessary existence. This would be illogical as a supremely perfect being must have 'all the perfections'. In Descartes argument he doesn't require the stating of a definition but instead relies on an innate idea of the perception of God. To further demonstrate his argument he used various analogies to convey the idea of inherent ideas. In one of these analogies he discusses how a triangle must have three sides or else it would cease to be a triangle. Similarly God must be exist necessarily as an innate concept as with the triangle. A being without necessary existence wouldn't be God, just as a shape without three sides wouldn't be a triangle.