Considering the major nosographies since Kraepelin, we underline the stability of the two classical functional psychoses and the difficulties in defining a satisfying classification of the intermediate forms. In an attempt to overcome the dichotomic view of the two traditional psychoses we propose a bidimensional model that is based on prototype descriptions of typical schizophrenic and affective disorders and allows the systematization of the intermediate forms. The advantages of this model are discussed with reference to therapy and prognosis and with regard to its relationship with clinical reality.