Chapter 5 marks the beginning of a more pointed analysis and justification of partial excuse across Part III, as the target site of the Real Person Approach. The chapter is concerned with exploring the nature and purpose of partial excuse through a historical overview, and with clarifying the version of the defence used to underpin the Universal Partial Defence (UPD), through touring divergent definitional and structural approaches of other common law jurisdictions. Key issues that bear on the definition of the UPD are also introduced. This analysis forms the backdrop of the argument for universalising partial excuse across all offence categories and expanding its grounds beyond mental disorder and provocation/loss of control. Core challenges to universalisation are explained and responded to, concerning the application of partial excuse to homicide only, its characterisation as a form of mitigation at the pre-verdict stage, and issues relating to both coordination and the notion of partial responsibility.