Dualism is an ancient concept which originated in Greece. The Greeks believed that a man's soul was entirely different from the body and these entities had no interaction with one another. The Greeks saw the body as the prison house of the soul. Therefore dualism can be referred to as the dichotomy of soul and body.
René Descartes (1596 - 1650), father of modern philosophy, was also a scientist, psychologist and a mathematician. Descartesviewed all physical bodies as machines operated by mechanical principles. According to him animal behavior and internal process could be explained mechanically as human behavior and human internal processes. The only difference between animals and human beings was that only humans possess a mind which provided consciousness, free choice and rationality.
Descartes used his famous saying as proof:cogito ergo sum, "I think, therefore I am." We cannot doubt our own existence, because we cannot doubt it unless there is a self to do the doubting. Descartes explained further what he meant with this, by stating:
" I then examined closely what I was, and saw that I could imagine that I had no body, and that there was no world nor any place that I occupied, but that I could not imagine for a moment that I did not exist.... therefore I concluded that I was a thing or substance whose whole essence or nature was only to think, and which, to exist, has no need of space nor of any material thing or body. Thus it followed that this ego, by which I am what I am, is entirely distinct from the body and is easier to know than the latter, and that even if the body were not, the soul would not cease to be all that it now is."
Though this idea is normally credited to Descartes, it was originated in about twelve hundred years before him. Augustine in hisCity of God(11.26) states that:
"Without any delusive representation of images and phantasms, I am most certain that Iam,and that I know and delight in this. In respect of these truths, I am not afraid of the arguments of the Academicians, who say, "What if you are deceived?" For ifIam deceived, Iam.For he who is not, cannot be deceived; and if I am deceived, by this same token Iam."
Descartes stated that human possess a body which operates according to physical principle, and a mind that does not. He held that the mind and the body had a completely different nature. However Descartes showed that there is a particular relationship between the mind and the brain. They are 'dependent upon 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.' (MMM 3) The soul was was present in all the parts of the body, but the removal of any part of the body would not reduce the soul. For Descartes the body was procreated and the soul was created. He explained this further by stating that even if some parts of the body were removed, for example; a leg, the soul was still indivisible. Though the soul and the body were developed from two different natures, they could still react upon each other. Therefore, the body makes an influence on the body and the body makes an influence on the soul. This type of dualism that Descartes was subscribed to is called interactionism, which is also referred to as Cartesian dualism. He actually became the father of the mind-body theory of interactionism.
The mind was described as non physical as it was not located anywhere specific in the body. Descartes believed that if the mind was not closely related to the body, we could not have any feelings like hunger, thirst or pain. Descartes wanted to find the exact place where the mind influenced the body. He sought a structure in the brain as the brain stored the animal spirits and it was the only place which he believed that is not duplicate like all other brain structures. According to Descartes this structure had to be uniquely human as only humans own a mind. Descartes decided to choose the pineal gland as the point of interaction as it was surrounded by animal spirits. Still the soul was not something which should be considered as trapped in the pineal gland.
When the mind desired for something to happen, it stimulated the pineal gland. This stimulated a certain area in the brain, in order to cause animal spirits to flow to various muscles and thus make possible the behavior wanted. Emotions are related to the amount of animal spirit involved in a response, the more animal spirit the more the emotion.
Descartes was always in search to find how a non physical mind could interact with a physical body. After several attempts he concluded that it cannot be explained logically, he decided to explain the mind- body relationship with common sense. He said that everyone has bodily and conscious
Most philosophers who followed Descartes rejected interactionism as it was not a testable hypothesis. This introduced the supernatural and so removed the concept from the scientific laboratory into the theological seminary. Other philosophers criticized his idea as they believed that if the soul and body are to substances of entirely different nature, then it is impossible for them to interact. Descartes disapproved with this, but he never satisfied his critics.