ABSTRACT
This chapter sets out how knowledge is acquired in somatic medicine and psychological medicine. It explains in which regards physical diseases and mental disorders are different. The specific nature of humans' mental life requires a specific method of acquiring knowledge about the origin and nature of mental disorders. The relation between the physical and mental is an important issue in any discussion about the differences between the etiology of physical diseases and mental disorders. There is one more point of difference between the etiology of physical diseases and mental disorders. There are as many etiologies of mental disorders as there are psychiatric models. The greater role of the personality in shaping the clinical picture of mental disorders is one of the reasons why diagnosing them is more demanding than diagnosing physical diseases. The personality's coping and defense mechanisms have a greater influence on the genesis and character of the clinical picture of mental disorders than that of physical diseases.
