Descartes reformed Anselm’s argument in the 1600s, setting about to prove God’s existence completely by reason and logic, with no dependence on the senses, which he believed to be deceptive and unreliable. Descartes argued that he was able to be sure of his own existence, by his ability to think and to doubt. He then went on to say that, his ability to conceive a perfect being in his mind would be impossible for him, as an imperfect being, to create. Therefore this concept must have originated from the perfect being itself. In order for that perfect being to be perfect, it must exist (drawing again on the idea that existence is a perfection)- therefore, Descartes argued that logically, God must exist.
Kant responded to Descartes’ version of the argument, claiming that existence is not a predicate, as Descartes seems to see it. Kant said that when we say that X exists, this does not tell us anything about X- existence of something does not add to our understanding of that thing- we must establish its existence before we are able to say what it is like, and not the other way around. Kant draws on Descartes’ claim that denying the existence of God is like denying that a triangle must have three sides: he agreed that if a triangle exists then it must have three sides, but argued that we cannot ascribe existence a priori to either the triangle, or to God- God’s existence is therefore separate from His existence, with no real consequence. Kant believed that existence cannot be proved de dicto in the way that Anselm’s and Descartes’ arguments try to prove it, and maintained that empirical evidence is our only means of drawing any reliable conclusions about the universe.
Both Anselm and Descartes assumed that we, as humans, are able to understand and define God using everyday language- a huge point of contention for believers. Aquinas criticised Anselm’s version of the argument for this reason, and accused Anselm of making an assumption about the definition of God not necessarily shared by all believers. However, if we accept Anselm’s definition of God, and thus accept the argument’s premises, the conclusion appears to follow logically from the premises- creating a valid, logically sound, deductive argument. Anselm also attempted to address the position of “the fool” (the atheist), saying that in denying the existence of God, the atheist must at least have a concept of God in his understanding- therefore if the atheist were to grasp the true meaning of God as ‘that than which nothing greater can be conceived’, then it should be a short step to their realising that it is logically impossible to deny such a being.
The argument’s a priori, analytic nature means that it is not contingent upon empirical evidence which may be proven false in the future, and, if accepted, it proves God’s existence as a logical necessity- as opposed to an a posteriori argument, such as the design argument, which can only prove the existence of God to be ‘highly probable’. However, this concept is problematic to empiricists such as Kant, who believe that sensory experience is the only way that we can draw conclusions about the world around us. Aquinas agreed with this idea, claiming that understanding the term ‘God’ can only prove that God exists in the understanding- not as an objective reality. Therefore he believed that in order to demonstrate God’s existence, we must apply inductive reasoning, drawing on our experience of the world. Aquinas and Kant both also criticised the jump from definition to reality that the ontological argument employs- Aquinas said this was “a transitional error”. Hume also raised this issue against the argument, claiming that it is impossible to define something into being.
In conclusion, the ontological argument can be viewed as a logically sound, deductive argument, which if one accepts the premises, proves God as a logical necessity; the argument also does not rely on empirical evidence, which can often be unreliable. Gaunilo’s criticism of Anselm’s argument has a major flaw, undermining its validity, and Anselm also attempts to address the position of the atheist, whilst Descartes uses a starting premise likely to be accepted even by the atheist. But, the argument views existence as a predicate- Kant disputes this, claiming that existence should be seen as something separate from definition, as the existence of an entity does not further our understanding of that entity. The argument also assumes that we God is understandable and definable in human language, and Aquinas disagreed with this idea, saying that Anselm’s definition of God cannot be shared by everyone. Furthermore, both Kant and Aquinas have argued that God can only be proved by empirical evidence, and have criticised the argument’s jump from definition to reality. Ultimately, the ontological argument may be a valid argument to a believer, but it is unlikely ever to convince an atheist of God’s existence.
