Mental disorders differ from so-called physical diseases in the sense that their limits are broader than those of the affected body since they cover the interplay of the individual and the environment. There are also some ontological differences between body and mind, and we grasp mental disorders in terms of reasons rather than causes, through a dialogue with the patient. The clinical manifestations may include fragmentation of the self; syntactic, semantic, and epistemic breakdown; a-rationality; breakdown of autonomy and of interpersonal relations. The classifications of mental disorders are generally free of aetiological assumptions. Psychiatry is one discipline and neurology is another, but even then, there is some shuttling back and forth between them. Psychiatric comorbidity and spectrum disorders tends to blur the distinction between clinical categories. Mental disorders are described by two types of predicates: P-predicates are those observed by a clinician, those applied to material human bodies. M-predicates include things like “is in pain”, “is anxious” or “has an auditory hallucination” that are perceived by the patient. The concept of mental illness spans what is felt but not observed by the patient and what may be observed, but not felt, by others. Mental disorders are being split from neurological disorders.