I frequently hear physician's voice the following argument with respect to sexual disorders and anxiety/depression, and I wonder of its validity: If there's a chemical treatment (e.g. pharmaceuticals) and it's successful, then the problem is physiological, not psychological. The argument appears invalid to me, because it seems to assume too large of a rift between one's psychology and one's brain. More exactly, if a chemical treatment works, and if one's psychology (i.e. thought-patterns and emotions) can have an effect on one's brain chemistry (and vice versa), then couldn't the problem still have a psychological source? It seems as if these physicians view psychology as having a basis in a something (a soul perhaps) that is causally independent of the brain. But that seems like an odd view for a Western physician to hold. I'd greatly appreciate any thoughts on this.

I agree that this reasoning seems strange. However, here's one possible justification for it. Any cause can be described in a large number of different ways. For example, a brick thrown at a window can be described as: (i) a brick thrown at a window, or (ii) the movement of a bunch of molecules through space. Which way we choose to describe a cause depends on our interests in the case. If we are interested in atomic physics, we may prefer description (ii); if we are interested in the movement of bricks in the area, we may choose description (i). Suppose that in medicine our interests are primarily to explain and treat disorders. For some disorders, it may be easier to explain and treat them by describing their causes in purely psychological language. For other disorders, it may be easier to explain and treat them by describing their causes in purely physiological language. There may also be difficult mixed cases, as you mention, in which the best strategy is to describe the causes in a mixed...