If a mental disorder referred simply to a collection of symptoms, then it could not be a cause of those symptoms. You are exactly right about this. A cause must be distinct from its effect. That is why we cannot say that my slamming the door was a cause of my shutting the door (where "slamming the door" is nothing more than shutting the door with some force). However, it is not at all obvious that the name of a mental disorder is simply the name for a collection of symptoms. On the contrary, the mental disorder's name might refer to a certain kind of cause of those symptoms -- perhaps a cause that is not yet identified at the time that the mental disorder was named. Then when the cause is later discovered, it is understood what the name of the mental disorder was referring to all along. Thus, a mental disorder can be a cause of some phenomena because it is distinct from those phenomena. The very same idea applies to the names of somatic (i.e., non-mental) disorders. A new illness (such as...

That a question begins from making false or impossible presuppositions does not keep us from understanding the question or responding to it with the correct (i.e., true) answer. After all, we know that I am alive today, yet we can reasonably assert things like "Had I been hit by a car while crossing the street yesterday, then I might well not have been alive today." We know what would count as evidence for this assertion (for example, facts about my anatomy, the speed of cars on the street, etc.). The fact that I was not, in fact, hit by a car while crossing the street yesterday does not prevent us from having justified beliefs about what would have happened, had I been hit by a car. Of course, it was *possible* for me to have been hit by a car. But it wasn't possible for Fermat's Last Theorem (a certain theorem about numbers that has recently been proved) to have been false. Long before this theorem was proved, mathematicians widely believed it to be true, since no one had ever found a...