Anselm's Ontological Argument

The field of ontology explores what it means for something to exist, it is the 'study of existence'. It is a priori therefore works from first principles and definitions to demonstrate the existence of God.

Anselm of Canterbury was a theologian and a philosopher. He proposed an ontological argument in his Prologion."The fool says in his heart, 'There is no God'". Anselm defines God as a 'being than which no greater can be conceived'. He suggested that even 'the fool' can understand this concept and to grasp this understanding itself causes the being to exist in the mind. The concept must therefore only exist in our mind, or in our mind and in reality. If such a being exists only in our mind, then a greater being -that which exists in the mind and in reality-can be conceived. Therefore the fool is a fool as you cannot accept the concept of God by mentioning him and not accept his existence.

Criticisms of Anselm's Argument:

• Anselm makes a jump from concept/idea to reality
• There are a variety of definitions of God; therefore his argument will only work if we accept the definition of God from Anselm

Gaunilo's Island:

He opposed Anselm and gave an immediate response to him he called 'on behalf of the fool'. Gaunilo states that just because a person can conceive of something, it doesn't make it exist. 

Anselm second ontological argument:

• Either god exists or he does not exist
• If God exists, his existence must be necessary
• If God does not exist, then his existence is logically impossible
• God is not a logically impossible thing
• Therefore, God's existence is necessary 
• Therefore, God exists