The DSM and ICD mental illness classificatory systems define mood disorder as essentially a single condition varying only by severity. Gordon Parker and Vijaya Manicavasagar expose the weaknesses in the existing models, and describe a new approach to sub-typing and managing depression based on there being some specific defined manifestations, including melancholia and psychotic depression, as well as versions of the condition highly dependent on life stresses and personality styles. They argue that depression can exist as a disease, a disorder, a syndrome and a normal reaction, and it therefore requires a multi-modal approach to conceptualization and management.