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.