if I see a mirage of a lake in a desert, the correct causal explanation of my vision does not involve the fact of any actual lake in the desert. In this case, my belief in the lake is not just explained, but explained away. But either way, the belief itself is a real phenomenon taking place in the real universe—psychological events are events—and its causal history can be traced back. “Why is there a lake in the middle of the desert?” may fail if there is no lake to be explained. But “Why do I perceive a lake in the middle of the desert?” always has a causal explanation, one way or the other.
