In order to criticise Descartes argument for the mind being non-material it is necessary to understand how he feel the two interact. The mind is associated in a particular way with the brain, yet they are separate entities, dependant on each other only as a fountain pen and ink are interdependent. The pen will not write without the ink and the ink carries no message without the pen. Sense perceptions and physical passions are dependent upon the body, but awareness of them lies in the mind. The important point then is how the mind becomes aware and how it succeeds in acting upon the body. Descartes held that the two components which constitute a human had an independent origin and are of a fundamentally different nature. The body could be divided up by the removal of a leg or an area, but the mind was indivisible. Though the two realities were of an entirely different nature, they could react on each other. The mind on the body and the body on the mind. The point of interaction according to Descartes was at the pineal gland. The mind was not to be viewed as somehow contained in the pineal gland. The gland is merely the point of interaction.
The great difficulty with this is how non-physical minds can interact with physical bodies. In Descartes own physics he states that forces are transferred by contact. However apply his physics to his Cartesian Dualism and he shows that the mind must be a physical entity. Taking Descartes argument that the mind is a non-material entity and therefore has no surface the body therefore cannot communicate with the mind because there is no surface to press on. The body cannot even hold the mind within it, since the mind has nothing to press upon to carry it in the body. Problems like these occur whenever the mind is described as being a non-material entity different from the body.
Our knowledge of Science has improved a lot since Descartes and it appears easy to jump to the conclusion that the mind and the body communicate by passing energy backwards and forth, which doesn’t require contact. But the presence of any energy in the mind would make it detectable in the laboratory as any kind of energy produces some heat it would be detectable. It would also violate the physical law of conservation. This states that there can only be a certain amount of energy within something that is a closed system. If the mind communicates with the brain there must be a transfer of energy. When the brain communicates with the mind it must loose energy and vice versa but the amount of energy is fixed within the closed system so how can the mind and the brain communicate?
Descartes argues that the ability to use and create language separates man from both the animal and the machine world. While a parrot may be able to repeat sounds, it cannot formulate individual thoughts. Descartes even envisions a machine that may be able to produce words, yet he argues that, being programmed by humans, it could not formulate its own sentences, merely copy those of its creators. To Descartes, animals and machines are similar in that they merely perform functions and exist as mechanisms, not as minds. He then expands the point to argue that the human capacity for language proves the existence of the non material mind: ". . . it would be incredible that a superior specimen of the monkey or parrot species should not be able to speak as well as the stupidest child, – or at least as well as a child with a defective brain – if their souls were not completely different in nature from ours." Due to the presence of organs similar to human organs in many animals, Descartes finds no material explanation of the lack of language in animals. The fact that animals can communicate vocally yet cannot use language indicates to Descartes the existence of a non-material mind in humans.
Yet this argument creates a problem for Descartes, both Liebniz and Locke argue that as animals and humans are of the same type, why do humans have minds and animals don’t? If you compare the least developed man with the highest developed animal there would probably be little or no distinction. Yet according to Descartes the human would have a mind the animal would not. Then take into account the theory of evolution and somewhere in our ancestry a mind just occurred. Churchland believes that evolution proves that humans are creatures made purely of matter. The course of human evolution developed the human brain to a more complex level than other species. Unique thinking processes and vocal abilities may have led to language in humans, separating them from animals not by some innate non-material soul, but though simple evolutionary divergence.
Descartes view is open to further criticism; Gilbert Ryle expressed this in what he referred to as “the ghost in the machine”. Descartes claims that there is a complex visible system called the physical body which has an engine which is an complex invisible entity called the mind, which takes on a spiritual form ever present in the body. Ryle uses a simile to express what he feels is a category mistake; a tourist is visiting Oxford, seeing the colleges and the library and then asking where the university is. Ryle considers the treatment of the mind as a different entity, separate from other parts of the body, rather than seeing it as one part of the processes of the human. According to Ryle there is thus no categorical difference between mental processes and physical ones.
Unfortunately science has yet to provide us with a concrete answer. There is no consensus on a satisfactory answer, however the arguments which I have analysed as presented by Cartesian Dualism which support the argument that ‘the mind is a substance that is not physical’ are clearly flawed.
