Chapter 2, “Sustainability as a failure of ontology,” considers the question of whether sustainability is a problem for Modernist rationality or a problem about Modernist rationality? Noting such things as the faltering information-deficit model, the diminished status of the ‘rational individual’ as meaningful unit of engagement, the loss of ‘natural objects’ as functional units of analysis, and the rise of Social Practice Theory, sustainability appears to be shifting from its basis in objective descriptions of planetary urgencies to a deep reflexivity regarding underlying dimensions of self and world. In response, we explore a series of linked strategies for conceptualizing and navigating such a revised sense of the sustainability challenge and identify the implications this holds for arts practices.