Jackson Kang

7/24/21

The Divisibility Argument

Rene Descartes was a firm believer in Cartesian dualism, or the belief that mental phenomena possess non-physical properties, while physical phenomena possess physical properties. Descartes attempts to provide support for Cartesian Dualism in the form of the Divisibility Argument: an argument that aims to prove that the body and mind are separate entities by providing three different premises. Furthermore, Descartes provides explanations regarding the truth of the premises, and responds to objections to the Divisibility Argument.

Descartes’ three premises of the Divisibility Argument are (1) the body/brain is divisible; (2) the mind is not divisible; (3) Leibniz’s Law is true, which eventually proves the conclusion: the mind and body are separate entities. As a believer of both substance dualism (The view that minds are immaterial substances and that there are also physical substances and properties that exist in the universe) and interactionism (the view that mental phenomena causally interact with physical phenomena), Descartes believes all his premises to be true. Premise one of the Divisibility Argument states that the body/brain is able to be divided, and is stated because the body can be physically separated into parts. Premise two of the Divisibility Argument states that the mind is not divisible: or in other words a mind cannot be divided into pieces like a physical body can. Descartes believes premise two because one’s mental consciousness and thoughts will never be two separate “voices”(normally), but instead one voice that is thinking to itself. Premise three of the Divisibility Argument states that Leibniz’s law is true. Leibniz’s law states that if two objects have the same properties, they are identical. Leibniz’s Law is essential in the Divisibility Argument because it proves soundness and validity of the argument. 

However, one could raise doubt towards Leibinz’s Law, for there are core flaws present in the law. Leibniz’s Law states that “there cannot be separate objects or entities that have all their properties in common and vice versa”: while one could not argue that there cannot be separate objects or entities that have all their properties in common, one could argue that the opposite is invalid. For example, if there are identical twins that are born from the same egg and sperm, share the same exact DNA, and look the same, their minds/mental phenomena will not be the same: in other words, they will not be carbon clones that act exactly the same. The “twins” example that was previously mentioned provides evidence as to why two identical entities do not have identical properties, thus proving Leibniz’s Law is false, further proving that the Divisibility argument is not sound. Moreover, one could argue that the premises beg the question, and one would only believe that they are true if they believe in mind-body dualism, discrediting the Divisibility Argument further. However, Descartes could counter the previous counter argument by stating that while the twins example could be used to prove Leibniz’s Law false, the twins minds were different from their identical bodies, proving that the mind and body are different entities. Either way, Descartes’ conclusion that the mind and body are separate entities are still proven true regardless of the counter argument. In conclusion, the Divisibility argument and Descartes’ response to the “twins” example provides validity and soundness to Descartes’ belief that the mind and body are separate entities.