To understand Anselms argument for Gods existence, one must first understand the principles that forms the argument. The first principle is the claim that nothing greater can be thought. There is too types of existing, existing in understanding (existing0) and existing in reality (existing1). Then, we try to think of something is existing1. Anselm let something be something than which nothing greater can be thought (NGT), or in another word a being than which nothing greater can be conceived according to the Proslogion.
The very first act of thinking that something is existing1 serves as the basis of it existing0. Because in the process of trying to think of something greater, we already establish its existence0. For example, there is a flower A, existing1. This flower A is the most beautiful flower, that this flower is a NGT. In order to prove this flower is NGT, one has to think of all the flower he has seen, flower B, C, or D. In the process of searching through ones mind trying to think of a flower that is more beautiful than flower A, flower A already exists in ones mind, which is existing0.
To open his argument, Anselm then said an example of NGT is God. The second principle is the principle of thinking of non-existing objects (Principle E). Anselm uses the example of a painter conceiving the drawing he will paint, then executing his plan in mind to make the painting exists in reality. To breakdown his argument, lets begin with something that exists0. Because one has the ability to imagine that something exists0, one can also imagine that the same thing exists1. This priniciple is the most uncontroversial because it is just a matter of imagination.
The fact that one has imagination allows him to imagine whatever he wants. For example, one imagines he won the lottery and has a million dollars. It is safe to say that one can proceed to think of that million dollars is existing1, regardless of if the million dollars truly exists1. Applying Principle E back to the argument of NGT, if one can imagine NGT in existence0, one can also go ahead and imagine NGT existing1. The third principle is thinking something greater than something (Principle G). This principle compares the greatness of existing0 and existing1.
Anselm proposes that greatness has two faces: qualitatively and existentially. To further support his argument, Anselm implies that greatness qualitatively means everything positive, such as, more beautiful, more knowledgeable, more influential, etc. Base on this assumption, Anselm argues that, Suppose it exists in the understanding alone: then it can be conceived to exist in reality; which is greater. To apply this principle in daily life, one can relate to a million dollars example above. One can imagine having a million dollars in his mind, but that million dollars doesnt exist1.
In another case, one owns a millions dollars, which means that million dollars exists1. The rhetorical question here will be, which case is more appealing to you, which scenario is greater? Back to Anselms claim, the it in his argument is, of course, NGT, which is God. That God exists1 is better than God only exists0 but not exists1. The next principle returns to the basic meaning of NGT. Principle N presents the idea if something can be thought to be greater than x, then x is not an NGT. Assume something is an NGT, nothing greater can be thought.
If there is another thing that is greater then it. This something is no longer an NGT. This principle is pretty self-explanatory. To put it in everyday examples, imagine the beautiful flower A is the most beautiful flower in the whole wide world. However, one found another flower more beautiful than A. Now A is no longer an NGT, regardless in existence0 or existence1. Now substitute God in for NGT in the equation. Because Anselm already claimed that God is an NGT, if one can think of something greater than God, God is no longer an NGT.
According to the Proslogion, God cannot be conceived not to exist. God is that, than which nothing greater can be conceived. That which can be conceived not to exist is not God. The upcoming principles idea bases that of principle E. Principle T simply proposes the idea that an NGT can be thought. Because one has the ability to think of an object either exists0, exists1, or even both, one can also think of NGT existing0, existing1, or both. The idea that one can think of something is very broad and universal, that something can simply be anything.
The final piece of Anselms argument is Principle M. This principle presents the very vague idea that if something must be thought as existing1, then it exists1. If one must think of a flower exists1, then that flower does exist1. Now that all principles Anselm needed to support his argument that God exists are gathered, he begins his argument with a fool (thinker) that understands [God] is in his understanding; although he does not understand it to exist. To fully understand this argument, one has to accept Anselms assumption that God, indeed, is an NGT.
The argument that the thinker has the ability to think of NGT existing1 is based on Principle E that if one can think of an object then he can think of it existing1. The idea of thinking NGT exists1 is greater than the idea of thinking NGT exists0 but doesnt exist1 (Principle G); therefore, one can think of something greater than the NGT that exists0 but not in reality. However, this violates the basic meaning of an NGT (Principle N), nothing greater can be thought.
So the idea that one can think of something greater than the NGT that exists0 but not in reality is contradictory to the fundamental element of an NGT. Which comes to the agreement that if one think of an NGT it is to be existing1. The conclusion implies the principle that one can thought of NGT exists1 (Principle T). Also, one can and must only think of an NGT exists1. This lead to the final conclusion. If one has no choice but think of something exists1, that something must be existing1 (Principle M).
Therefore, an NGT, God, exists. Aquinas gives an condensed version account of Anselms argument in Summa Theologica. In objection 2 of question II, Whether the existence of God is self-evident? , Aquinas addresses the idea much abruptly. He first implies that Anselms idea of God is an NGT is equivalent to saying things are said to be self-evident which are known as soon as the terms are known, that the significant of the word God is nothing better can be conceived.
He follows the account by stating that the word God exists actually and mentally is greater than that which exists only mentally. Therefore, if the word God is understood mentally it has to be understood to exist actually. Both Anselms argument of Aquinass account of it come to the same conclusion that God exists, that the thought of it existing lead to its real existence. Aquinas objects Anselms idea by stating that not everyone understands the word God will agree that it is an NGT. He follows his objection by stating:
Yet, granted that everyone understands that by this name God is signified something than which nothing greater can be thought, nevertheless, it does not therefore follow that he understands that what the name signifies exists actually, but only that it exists mentally. Aquinass main objection is that the idea of NGT can be interpreted that it can only exists mentally. However, for Anselms argument to work, one has to understand that God can exists in reality; therefore, Aquinas further objects Anselms claim by stating those who hold God does not exist will not admit the fact that God is an NGT and it exists in reality.
In Anselms defense, he based all his argument on the fact that God is a being than which nothing greater can be conceived. As a true believer of God, Anselm would have simply oppose those who does not believe in God has not fully understand the meaning of God; therefore, they fail to grasp the idea God exists in reality. If one understands God, he will be able to think of Gods existence in mind then agree to think of it in reality. After reading excerpts both from the Proslogion and the Summa Theologica, I am more inclined to support Aquinass claim.
Although I do not think Aquinas has successfully destroyed Anselms argument, I think there are more weak links in Anselms argument than that of Aquinass. The most apparent loopholes are Principle M and Principle G. First, Principle M states that if one has to think of something as existing1, then that something has to exists1. However, Anselm neglects the fact that what one believes exists1 does not has to be true. For example, children were told to believe Santa Claus exists in reality and many of them do believe that idea.
The contradiction being what those children can and must think exists1, Santa Claus, does not exists1. Second, the positivity of greatness implied in Principle G is too vague. The concept of greatness of reality is better than that of in mind can be subjective. Just because one person thinks the existence in reality is greater than existence in mind does not equal others perception of greatness. With doubts in Principle M and Principle G, I think Aquinas has a stronger position compare to Anselm does.