Physical System
The theoretical distinction between body and soul is ancient. We assume that physical and psychological processes conform to separated systems which are closely bound with each other. Neither system has a choice as to whether it wishes to engage with the stimuli which the other system makes available. They are, in a manner of speaking, under a ‘resonance constraint’. A psychological process finds a physical expression and a physical phenomenon undergoes a psychological reaction. Therefore, physical interventions, or interventions which focus on the body, produce psychological effects and psychological changes have physical effects.
What is important here is that the coupling affects the entire body and not only the brain. The physical counterpart of the soul is the body, not the neuro-biological metabolism in the brain. A very useful distinction in this context is between the body and the embodiment. The organismic body becomes the embodiment when it is perceived (and, therefore, is a phenomenon in consciousness). Accordingly, one does not have a body, but one is an embodied process.