To whatever extent mental defect and mental illness arc organically caused, the psychological theories overlap with the biological theories. There is no doubt that mental illness and personality maladjustment are associated with some kinds of deviant behavior. This lias to be true since deviant behavior is often used as a symptom in diagnosing mental illness.
One is diagnosed as mentally ill because of one’s deviant behavior, and then this deviant behavior is attributed to the mental illness. It goes like this: “He is deviant because he is mentally ill.” “What makes you’think he is mentally ill?” “His deviant behavior Deviant behavior is not the only symptom used in diagnosing mental illness. It is probably true that some deviation is caused by mental illness. It is also true that mental illness or serious personality maladjustment is not much more common among deviants than among other people [Pfuhl, 1979, p. 48]. Thus, psychological theories are not very helpful in explaining deviant behavior.