There have been many NIME papers over the years on augmented or actuated instruments . Many of these papers have focused on the technical description of how these instruments have been produced, or as in the case of Machover’s ‘Hyperinstruments’ , on producing instruments over which performers have ‘absolute control’ and emphasise ‘learnability. perfectibility and repeatability’ . In contrast to this approach, this paper outlines a philosophical position concerning the relationship between instruments and performers in improvisational contexts that recognises the agency of the instrument within the performance process. It builds on a post-phenomenological understanding of the human/instrument relationship in which the human and the instrument are understood as co-defining entities without fixed boundaries; an approach that actively challenges notions of instrumental mastery and ‘absolute control’. This paper then takes a practice-based approach to outline how such philosophical concerns have fed into the design of an augmented, actuated cello system, The Feral Cello, that has been designed to explicitly explore these concerns through practice.