Philosophical Arguments for God’s Existence


The existence of God is one of the oldest debates in the history of humanity, and the topic is still extremely popular today. Anselm of Canterbury was among the first philosophers to present arguments that explain why God should exist. The thinker’s ontological argument was provided in his Proslogion and followed by critical responses from different philosophers, including Aquinas, Guanilo, and Kant. This essay explains and analyzes the main points of Anselm and his critics.

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Anselm’s Ontological Argument for God

As a typical example of ontological proofs, Anselm’s argument starts with the provision of definitions helping to better understand the term “God.” Anselm describes God as the greatest and the most perfect creature that can be imagined, understanding him as “that than which nothing greater can be thought” (Millican, 2018, p. 19). Next, based on the presented common truth, he concludes that God is an idea that exists in people’s mind (Millican, 2018). This premise lays the ground for further conclusions and allows comparing different types of ideas.

If God is an actually existing idea, he can be compared to other beings, and Anselm uses it in the third premise. According to it, if there are two equal beings, one of which exists as an idea, whereas the other is an idea that can also be found in reality, the second being is always greater (Millican, 2018). As is clear from Anselm’s works, he puts a deep meaning in the category of “greatness.” To him, a being that is actually great should exist in reality and possess a number of divine qualities, such as “omnipotence, omniscience, and omniperfection” (Millican, 2018, p. 21). Using the example of these two beings, Anselm proceeds to the fourth premise. Based on it, if God is nothing more than an idea, a being that is greater than God can be imagined (Millican, 2018). At this point, he introduces logical inconsistencies and goes back to the first premise to show that God is the greatest being by definition. Taking that into account, the philosopher proves that God should exist if the definition of this being is correct.

Three Criticisms of Anselm’s Argument

Anselm’s ontological argument was criticized by many prominent philosophers, including Thomas Aquinas. Just like Anselm, Aquinas was a believer, but he did not think that the ontological argument was logically correct due to different definitions of God (Millican, 2018). According to Aquinas, there is no universal idea of God, and not all people would agree with Anselm’s definition presented in the first premise. Therefore, Anselm’s ontological argument should work only when explained to people who perceive God as the greatest being ever (Millican, 2018). The next problem raised by Aquinas is people’s inability to understand Anselm’s definition of God. To him, infinite concepts that lie beyond the boundaries of human perception can never be fully understood by the finite mind (Millican, 2018). Based on that, by using definitions such as “that than which nothing greater can be thought,” one encourages other people to “translate” them into a more finite language (Millican, 2018, p. 19). As people have to use external concepts and something that they already know to grasp the meaning of this definition, it becomes distorted, thus placing the argument’s correctness into question.

Anselm’s position on God’s existence was also critically scrutinized by Gaunilo, a French monk. In his famous Perfect Island objection to Anselm’s works, he demonstrates the ontological argument’s flaws by using it to prove the existence of absurd or illogical concepts (Pezet, 2018). He introduces the notion of a piland defined as “the greatest island that can be conceived” and follows Anselm’s logic accurately to conclude that pilands should exist in reality (Pezet, 2018, p. 72). Using Anselm’s logical algorithm, Guanilo claims that a piland that can be found both in people’s mind and reality is far more perfect than another piland that exists only as a concept (Pezet, 2018). Despite significant differences between the properties of God and Gaunilo’s island, the thinker provides a rationalization for piland’s existence. Then, he makes a conclusion that the ontological argument cannot be accurate and correct if another argument constructed by analogy is absurd.

The third famous objection to Anselm was presented by Immanuel Kant. Unlike Guanilo, Kant focuses on the flaws of particular premises in his critical responses. For instance, he aims to disprove Anselm’s third premise that introduces the relationships between existence and different creatures’ degrees of perfection. To Kant, the third premise involves understanding existence as one of the properties that make things more perfect (Proops, 2015). Kant claims that being or existence “is not a real predicate” and cannot be regarded as a property because having properties already involves existence (Proops, 2015, p. 1). Therefore, it is more accurate to define existence as a precondition, without which beings or objects cannot have properties and manifest them. Kant also disagrees with Anselm’s position on the ability of existence to make things better and greater, and he demonstrates it using the example of one hundred thalers (Proops, 2015). In his opinion, if understood as an abstract debt, one hundred thalers in a person’s mind is not a larger sum of money than the same thing in reality.

Argument Evaluation

Personally, I disagree with both the approach that Anselm takes to prove God’s existence and Guanilo’s response to it. For the entire ontological argument to be correct, the definition of God provided by Anselm has to be accurate, clear, and complete. However, Anselm does not explain why God’s ultimate greatness cannot be brought into question. Also, his first premise seems to show that people know nothing about God because the definition involves facts that cannot be checked by people.

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To continue, God’s being greater and more perfect than anything else can only be proven and understood by creatures that know everything about anything, but no person meets these criteria. Therefore, I agree with Aquinas’s counterargument, according to which people’s inability to understand the concept of ultimate greatness weakens the proof (Millican, 2018). Kant’s claims can also be regarded valid since it is doubtful that existence can make something more perfect. For instance, if a thing exists only as an idea, it is not subject to the laws of physics, changes in time, and other factors that make real things’ imperfections manifest themselves. Concerning Guanilo’s objection based on analogies, it seems that the thinker draws parallels between drastically different concepts. An island is something that people are familiar with – they know what it looks like and what physical properties it can possess. The same statement does not apply to God, which makes such comparisons unjustified.


To sum it up, Anselm’s argument is aimed at proving the existence of God as it is understood in Western religions. Anselm’s ontological proof was criticized with attention to the logic of both the entire argument and its particular premises. The critics’ main points included the inability to construct one definition of God that could be applied universally, the doubtful status of existence as a property, and the argument’s applications to absurd concepts.


Millican, P. (2018). Anselm. In G. Oppy (Ed.), Ontological arguments (pp. 19-43). Cambridge, United Kingdom: Cambridge University Press.

Pezet, R. E. (2018). An impossible proof of God. International Journal for Philosophy of Religion, 83(1), 57-83.

Proops, I. (2015). Kant on the ontological argument. Noûs, 49(1), 1-27.

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