One difficulty which hinders the advance of psychiatry is that the facts of a mental disorder are not easy to describe and to record accurately. Many of the descriptive words used, such as “depression”, “confusion”, are taken from common speech and carry with them vague meanings. Out of sympathy with the sufferer, we tend to read our own emotions into the clinical picture. Moreover, because a disorder of thought and behaviour is a disorder of adaptation to living, the description of a mental disease involves not only the recording of the symptoms, but also a description of the circumstances and life-setting in which they occur. Another difficulty lies in the great variation in the clinical pictures of mental disorder. These vary so much that a diagnostic label such as affective psychosis or schizophrenia does not convey, and indeed is not intended to convey, an idea of a specific disease. These difficulties are somewhat more marked in the investigation of mental disorder in contrast to the investigation of mental defect. The statement that a patient is a Mongol or a cerebral diplegic conveys the idea of a fairly definite clinical syndrome, whereas a statement that a person suffers from schizophrenia calls up a much less clear mental picture. It seems that the only way out of this difficulty is to give a short statement of the clinical facts about each psychotic whom one discusses.