Defining Normality, Abnormality, and Classifying Disorders

One of the oldest and most difficult problems in clinical psychology is deciding what counts as a psychological disorder at all. Before a clinician can diagnose or treat, a society and a profession must first agree on where ordinary human variation ends and where disorder begins. This boundary is not fixed. It shifts across historical periods, cultures, and even individual clinicians, which is why abnormal psychology treats the concept of "abnormality" as something to be examined critically rather than assumed.

Psychologists have offered several ways of defining abnormality, each with strengths and weaknesses. The statistical infrequency approach treats behaviour as abnormal when it is rare in the population. Yet rarity is not the same as disorder: extremely high intelligence is statistica