This article considers the notion of the invention as an instrumental concept in designing an interactive music system. The derivation of the idea is traced from Dreyfus' Bach and the Patterns of Invention. Issues of the nature of the interactive musical context are problematised on the basis of ideas from Adorno and Lyotard. The invention is presented as a mechanism for implementing the concepts of the embodiment and distribution of musical activity, which are shown to be generalisable. The relationship of composer and computer is considered in the light of a ‘prosthetic culture’. It is suggested that a crucial property of the invention is that of self-simulation.