Arguments from reason

• Anselm of Canterbury was a monk, philosopher, and theologian who lived in the middle ages.

  He argued for the existence of God a priori, using the ontological argument, which is found in Proslogion. He quotes Psalm 14:1 - 'the fool says in his heart that there is no God.' He aims to disprove this fool
• Anselm's argument is as follows:

  God is the greatest conceivable thing.

  Anything which really exists is greater than a thing which exists only in the mind.

  So, God must exist, in mind and reality, to be the greatest conceivable thing.

  Anselm argues that the fool has not considered the true definition of God.
• Gaunilo was an 11th century monk and empiricist. Although he believed in God, he criticised the ontological argument.

  He argued that Anselm's logic could be used to prove anything exists. For example, a lost island greater than any other islands.

  He also argued that it is difficult to imagine God, as we have never seen him, and this is the problem with a priori arguemnts.
• Descartes' ontological argument is found in Meditations on First Philosophy Book V.

  He defines God as supremely perfect, which included omnipotence and omnibenevolence. Existence is a real predicate of supreme perfection, so the concept of God cannot exist without the actual existence of God.

  This would be as illogical as saying a triangle can exist without three sides.
• Immanuel Kant was an 18th century German philosopher.

  Kant disagrees with Descartes and Anselm, as he says that the statement 'God exists' is synthetic, not analytical.

  He uses Descartes example of a triangle, saying we can simply reject the existence of a triangle, and its three sides.

  So, we must use empirical verification to prove that God exists.
• Kant also points out that the ontological argument wrongfully uses existence as a real predicate. The quality of existence does not change the concept of something - so cannot be a predicate. This means that existence cannot be a part of the concept of God.

  So 'God exists.' is not an analytical preposition.