In Proslogion 3, Anselm continues with his priori argument into the existence of God. Anselm defined God as a being that nothing greater than which can be thought of. In Anselm’s second version, a further point is added that something, which cannot be thought not to exist, is greater than anything, which can be thought not to exist. Anselm thought it was impossible to think this of God. Anselm’s second argument concludes that God has to exist and cannot fail to exist (necessary existence). Anything, which has to exist and cannot fail to exist is said to be “necessary”. Most things that exist depend on something else for their existence (contingent existence).

Anselm constructs his first argument across Proslogion 2, presenting his overall argument towards God existing in reality. Anselm defines God as the greatest possible being that can be conceived and that God may exist either in the mind alone (in the intellectu) or in reality (in re) as well. Something, which exists in reality and in the mind, is greater than something that exists in the mind alone. For example if a painter were to imagine (in intellectu) a drawing that they could potentially create this would not be as great as the reality ( in re) of the drawing. Due to God being defines as that which nothing greater can be conceived, he must possess all perfections, therefore God must exists in reality and in the mind. Anselm’s argument is a reply to the fool from the bible (Psalm 14:1) that says, “There is no God”. Anselm suggests for the fool to say there is no God, they must have an idea of God in their mind, which Anselm believed the definition in the mind is that ‘God is the greatest possible being”. Anselm then concludes that God is the greatest possible being that an be “conceived”. Anselm thought that what exists in reality as well as the mind is greater than something that is only an idea.