Arguments based on reason

• Deductive: If the premises of the argument are true then the conclusion must be true 
• A priori: Truth assessed before experience  
• Analytic: Statement is true by definition 
• The Ontological Argument was developed by Anselm. He set out to prove God’s existence using his logic alone with no empirical evidence.
• Anselm wrote a book called Proslogism.  
• Anselm used the following premises to reach the conclusion

  1. God is defined as 'that which nothing greater can be thought'
  2. Things can exist in both mind and reality
  3. It is better to exist in reality
  4. Therefore, God must exist in reality to be the greatest.
• Gaunilo was a monk like Anslem, but he challenged Anslem's logic via reductio ad absurdum. This meant that if you failed to follow the argument logically, it would lead to an absurd consequence. 
• Gaunilo challenged Anslem on the grounds: 

  • You cannot demonstrate the existence of something simply because you have an idea of it. 
  • There are a lot of things that exist in people's minds that do not exist in reality. 
• Gaunilo uses the analogy of the perfect island
• Anselm replies to Gaunilo's criticism:

  1. An island is contingent  
  2. Any contingent thing can be conceived as not existing 
  3. By contrast, a being that ‘than which none greater can be conceived’ cannot not exist. 
  4. God's existence is therefore necessary. 

   
• Other forms of ontological argument: AAND
• Descartes: God's existence is apart of his essence

  1. God by definition is a ‘supremely perfect being’ 
  2. A supremely perfect being has all perfections or qualities 
  3. Existence is one of these perfections 

  “Existence is a predicate” 

  
  

  4. Therefore, God has existence, he exists 
• Alvin Plantinga:

  1. I can imagine a possible world where a being of maximal greatness exists.  
  2. If it is a maximally great being, it must exist in all possible worlds including ours.  
  3. Therefore, a maximally great being must exist.  
• Norman Malcom:

  1. God has to exist necessarily
  2. Nothing could have brought him into existence
  3. So, existence is a predicate. It is the very definition.
• Main Criticisms: 'Go Kick Russel and Aquinas'
• Kant:

  • Existence is not a defining word because it requires evidence 
  • Anselm was using analytic (ideas about triangles) but tried to apply to a synthetic (real things such as God is real) 
  • Synthetic statements require evidence 
• Aquinas:

  Can only prove God exists through an a posteriori approach (with evidence) 
• Russel:

  • Existence is not a predicate. It isn’t logical to add existence to something in order to define it.  
  • E.g. Santa is a man. Men are real. So, Santa is real.