Depression, like many other mental disorders, is characterized by the presence
of a number of symptoms which are changeable over time. These
symptoms cluster together in several combinations and they present an
infinite variability at the individual patient level. Grouping these symptoms
and signs together, according to their shared features, is a necessary
step to understanding their psychopathological substrate, to uncovering
their underlying consistencies and eventually their common mechanisms, as
well as to accomplishing our clinical responsibility to predict their course
and effectively control them. Up to now no common causes for depressive
disorders are known that would allow for an etiologically based (true) classification.
Neither are there any biological markers available, which would by
themselves reliably and validly secure a biologically based diagnostic classification.
We have, therefore, to rely mainly on symptoms and the clinical
and familial characteristics of the patient in order to formulate a typological
diagnostic categorization. The assessment of symptoms, on the other hand,
is judgment-based, since there are no pathognomonic symptoms or categorical
cut-off points on depression measurements that would adequately
define and diagnose a ‘‘case’’ of depression.

Historical Background

Descriptions of depression and depression-related mental disorders date back to antiquity (Summerian and Egyptian documents date back to 2600 BC). However, it was Hippocrates (460–370 BC) and his disciples who first studied these conditions systematically and introduced the term ‘‘melancholia’’ to describe the symptoms and to provide a physiological explanation of their origin. The Hippocratic School attempted to link the balance of the postulated four humors (blood, yellow bile, black bile and phlegm) with the temperament and personality, and the latter two with the propensity to develop one of the four diseases (mania, melancholia, phrenitis and paranoia). It is interesting that Hippocrates considered symptom duration as a diagnostic criterion for melancholia by stating in one of his aphorisms that ‘‘if sorrow persists, then it is melancholia’’. Subsequent eminent authors of antiquity (Aretaeus of Capadokia, Galen and others) continued using the term melancholia and elaborated further on its symptomatology, its causation and its delineation from related disorders. The essentials of the traditional views on melancholia were retained during the middle ages and long after. The publication of Robert Burton’s Anatomy of Melancholy in 1621, in addition to presenting an excellent description of a sufferer’s feelings, provided an informative review of the prevailing concepts on the nature of the illness at the time. The term ‘‘melancholia’’ survived as the only specifier of morbidmood and disposition until Kraepelin, at the end of the nineteenth century, introduced the term ‘‘manic-depression’’ to separate nosologically mood disorders from dementia praecox, known after Bleuler as schizophrenia.