Disgusted by the developing tide of psychiatric eugenics championed by the Nazi Party, Schneider left the institute, but did serve as a doctor for the German armed forces during World War II.
[6] After the war, academics who had not taken part in the Nazi eugenics policies were appointed to serve in, and rebuild Germany's medical institutions.
Schneider’s publication, “First Rank Symptoms,” remains one of his most notable contributions to the field of psychiatry and outlined the diagnostic criteria for schizophrenia.
[8] His paper, The Stratification of Emotional Life and the Structure of Depressive States, was noted as one of the first applications of phenomenological philosophy to psychiatry.
The reliability of using first-rank symptoms for the diagnosis of schizophrenia has since been questioned,[14] although the terms might still be used descriptively by mental health professionals who do not use them as diagnostic aids.
This was based in part on his earlier 1921 work 'The Personality and Fate of Registered Prostitutes' where he outlined 12 character types.
Schneider's work in this respect is said to have influenced all future descriptive typologies, including the current classifications of personality disorders in the DSM-V and ICD-11.
[18] In fact, Schneider's mixing of the medical and the moral has been described as the most noteworthy aspect of this work, which has been linked back to German reception of Cesare Lombroso's theory of the 'born criminal', redefined by Emil Kraepelin and others (see also Koch) in to psychiatric terms as a 'moral defect'.