I don't want to take the time to write it up this morning but maybe I can at least get my juices going by jotting down some thoughts on Descartes and the soul.
1. First, there is the shift from viewing the soul as material to viewing it as immaterial. This shift goes along with the invention, so to speak, of nature by Descartes. This is the dividing up of the world into natural and supernatural, the material and the immaterial. Before creation was more of a continuous spectrum from embodied to thin, disembodied material (cf. Dale Martin).
2. Descartes letters to the princess of Holland, where she takes him to task--how can the immaterial have an effect on the material? He suggests maybe it is something like gravity. He locates the soul in the pineal gland. The body is a machine (Treatise of Man, Passions of the Soul). Thoughts are formed in the pineal gland:
Even though the soul is joined to the whole body, "nevertheless there is a certain part of the body where it exercises its functions more particularly than in all the others... The part of the body in which the soul directly exercises its functions is not the heart at all, or the whole of the brain. It is rather the innermost part of the brain, which is a certain very small gland situated in the middle of the brain's substance and suspended above the passage through which the spirits in the brain's anterior cavities communicate with those in its posterior cavities. The slightest movements on the part of this gland may alter very greatly the course of these spirits, and conversely any change, however slight, taking place in the course of the spirits may do much to change the movements of the gland" (Passions of the Soul).
3. Passions can affect the soul. Prior to him only the soul affected the body, not the other way as well.
4. Soul is simple and indivisible, potentially infallible in its detachment from the material world, able to look on objectively.
5. Descartes represents a shift from seeing the soul as the principal of life to the principal of thought. The soul becomes the seat of the "I." This leads to an introspective trajectory for Western culture.
I may add more notes today as thoughts occur...