Much of professional therapy is helping medically "normal" people with developmental and/or environmental problems. Still, a therapy setting according to the medical model calls for knowledge of abnormal development assessments based on the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders.

Biological Viewpoint of Mental Disorders:

The idea of a causal, empirical link between mental disorder and brain malfunction appeared during the Age of Reason and was widely accepted in the 19th century. Spurring further classification of illnesses and research into their physiological processes, the work of William Griesinger and Emil Kraeplin influenced this biological view.

Psychosocial and Sociocultural Viewpoint of Mental Disorders:

With the start of the 20th century, psychology became accepted as a recognized discipline. This promoted investigation of psychological causes for behavioral problems. According to Coleman, et al., there are five views of human mind and nature that reveal the psychological perspective:

1. Psychoanalytic
2. Behavioristic
3. Humanistic
4. Existential
5. Interpersonal