Kraepelin acknowledged that "there are many overlaps in this area," that is, the area between schizophrenia and mood disorders. In 1959, psychiatrist Kurt Schneider (18871967) began to further refine conceptualizations of the different forms that schizoaffective disorders can take since he observed "concurrent and sequential types". (The "concurrent type" of illness he referred to is a longitudinal course of illness with episodes of mood disorder and psychosis occurring predominantly at the same time called psychotic mood disorders or affective psychosis; while his "sequential type" refers to a longitudinal course predominantly marked by alternating mood and psychotic episodes.) Schneider described schizoaffective disorders as "cases in-between" the traditional Kraepelinian dichotomy of schizophrenia and mood disorders.