Descartes’ explore for certainty started out with doubts. He professed that as he had admitted many false opinions as true, his knowledge is dubitable; hence his beliefs are based on unsettled assumptions. Thus, he decided to reconstruct his views upon sound principles. Descartes wisely undermined the foundations of his understandings so that the rest of his thoughts would collapse consequently. To do so, he tackled the validity of senses-acquired knowledge. He also considered the possibility of being deceived, not only about the testimony of the senses, but also about the truth of arithmetical axioms and logical principles (Descartes, 2008, p. 14).
As a religious person, Descartes rejected the possibility that God is deceiving him. However, he did not turn down the existence of a cunning evil demon devoted to deceiving by illusions and by interference with senses and understandings. Descartes argued that he can grant the logical possibility of the existence of such an evil demon and thereby doubt the certainty of his fundamental beliefs. Even though, he cannot doubt that he is a thinking thing, regardless of his body and senses. Therefore, he took this certainty as the unshakable cornerstone of knowledge: “I am; I exist” (Descartes, 2008, pp. 16-18).
Descartes in the sixth meditation pursued his project and examined the existence of material things. He argued for the difference between pure intellect and imagination using the example of a triangle and a chiliagon to show how understanding differs from imagination and is independent of it. He declared that while the mind does understand, it faces to itself, but while it does imagine, it looks toward the body and works with its acquired knowledge through senses. Using ‘different property’ argument he referred to some properties, such as divisibility and spatiality, which pertain to material things but not to the mind. Therefore, he implied his substance dualism theory by claiming that the mind is not a material thing and is independent of it. He added although the mind and the body are highly inter-correlated with causal interactions, the former can exist without the later (Descartes, 2008, pp. 51-56).
Descartes’ dualism encountered with some objections, specifically about the mechanism of interactions between the body and the mind. It was questioned by Princess Elisabeth that how exactly immaterial mind can affect and move the material body while it has no spatial property like shape, size and mass. Some behaviourism and identity theorists criticised the substantial dualism and debated that the mind is the brain like water that is nothing more than two atoms of Hydrogen and one atom of Oxygen set in a particular composition. Therefore the mind’s features and properties can fit into physical existence as it is just another material thing. They justified humans’ perspective of their mind as how it looked from inside that is just another way of interpreting the same thing. Thus, there is no need to posit metaphysical nature for the mind (Descartes, 2008, pp. 51-56).
Identity theory resolves some criticisms that dualism was encountered concerning the interactions between the mind and the body. However it leads to Eliminativism, that mind and brain are one entity, which is not broadly acceptable by humans’ common sense. Descartes’ dualism faced other criticisms such as damage minds as well.
Descartes, René, and Michael Moriarty. Meditations on First Philosophy with Selections from the Objections and Replies. Oxford: Oxford University Press, 2008.