AbstractCritical Systems Thinking (CST) has traditionally sought its philosophical underpinning in the work of German theorist Jurgen Habermas. We suggest that CST need not necessarily be informed by Habermas, and present the thought of Michel Foucault as one possible alternative. This paper traces the historical development of the relative positions of Habermas and Foucault and examines the differences between the two with regard to systems. Our aim is to spark and inform debate within the systems/OR community as to the relative merits of each as a basis for CST.