Thus the use of recreational and therapeutic drugs provides overwhelming evidence that changing
brain processes causes changes in mental processes. Of course, the precise effects of drugs often
depend on expectations, as when people get more drunk than normal on a small amount of alcohol just
because of their social surroundings. So it is legitimate to say that mental processes cause brain
processes too. After all, the mind-brain identity theory just says that mental processes are brain
processes, and there is no problem in saying that brain processes cause other brain processes. More
importantly, these expectation effects provide no evidence for reintroducing the soul or other
nonmaterial substance into explanations of brain changes, because beliefs can be understood as neural
processes.