Psychopathological symptoms are the hallmark characteristics in all schizophrenia constructs all along the history since non-clinical domains have never been included in any of the major diagnostic criteria systems applied to schizophrenia.

Despite the critical importance of the DSM system in psychiatric nosology, a problem that is still not completely solved is clinical heterogeneity of patients, which it is not the exception but the rule. The magnitude of the problem is well illustrated by an example: There are 25 different combinations of characteristic symptoms (Criterion A), 5 schizophrenia subtypes and 9 longitudinal courses for ‘DMS-IV-TR’ schizophrenia disorder. Taken together, 1125 different clinical forms are possible for the same diagnosis.

Categorical approach to the assessment of symptoms and syndromes/disorders should be supplemented by dimensional analyses both at clinical and research levels. In fact, treatments for schizophrenia patients are mainly selected by their predominant symptoms and not exclusively by their diagnoses.