Descartes investigated the connection between the mind and body, and how the two interact. His main influences for dualism were theology and physics. The theory on the dualism of mind and body is Descartes’ signature doctrine and permeates other theories he advanced. Known as Cartesian dualism, his theory on the separation between the mind and the body went on to influence subsequent Western philosophies.
According to Descartes two substances are really distinct when each of them can exist apart from the other. Thus Descartes reasoned that God is distinct from humans, and the body and mind of a human are also distinct from one another. He argued that the great differences between body and mind make the two always divisible. But that the mind was utterly indivisible, because “when I consider the mind, or myself in so far as I am merely a thinking thing, I am unable to distinguish any part within myself; I understand myself to be something quite single and complete.”
Descartes’ dualism of mind and matter implied a concept of human beings. A human was according to Descartes a composite entity of mind and body. Descartes gave priority to the mind and argued that the mind could exist without the body, but the body could not exist without the mind.