In this chapter we consider the conflicts between two traditions of political ecology. The two traditions might be crudely characterized as physicalist and culturalist. The first is apparent in much of the work in ecological economics in particular, but also in the materialist left and more practically in conservation policy. It is concerned with the physical and bio physical conditions for human and non-human flourishing. It typically employs physical indicators of human well-being and biophysical indicators of environmental change. It is typically concerned with the ways in which current economic and social systems meet physical limits in the capacity of the environment for resource provision, waste assimilation and climate regulation. It is science based. In the tradition of ecological economics one can trace the influence of an older physicalist tradition found in the work of the left Vienna Circle, and in particular of Otto Neurath. The second tradition is apparent in a body of work that sees the environmental crisis as part of a wider cultural crisis in ‘Western reason’. It is typically more critical of science and scientism as forms ofideology that are taken to underpin the environmental crisis. The reduction of practical reason to modes of instrumental rationality limits the possibility of a critical perspective on our environmental problems. One of the main sources of this body of work is the Frankfurt School.This outline of the two traditions is crude. However, it does reflect areal tension within political ecology and the environmental movement more generally, in particular in its ambivalent relation to the natural sciences. On the one hand, the environmental movement is one that is science dependent. More than any other political movement it is reliant on scientific claims. Most environmental problems, such as those associated with climate change or rates of biodiversity loss, could not be even identified without the natural sciences. However, on the otherhand, it is a movement that contains within it strong elements of science scepticism ranging from the concerns about the conflicts between scientific expertise and demands of democratic participation through to views that the sciences themselves are one source of the very environmental problems the sciences have identified.In this chapter we examine one of the historical roots of the opposition between these two traditions of political ecology, in the debates between the left Vienna Circle and the Frankfurt School. In doing so we suggest the basis for at least a partial reconciliation. The chapter is in five sections. In Section I we outline the history of the conflict between the two traditions in some largely forgotten debates between Neurath and Horkheimer in the 1930s. In Sections II, III, and IV we examine thehistory and influence of the Vienna Circle and Frankfurt traditions by placing Horkheimer’s and Neurath’s papers in a larger narrative arc: the second and third outline the influence of the work of the Vienna Circle in the development of the tradition of ecological economics; Section IVconsiders the critique of instrumental reason that emerged from the Frankfurt School, developed in part in opposition to the positivism ofthe Vienna Circle. In Section V we consider the legacy of the debate andoutline some of the virtues of the approach offered within the tradition ofthe Vienna Circle, in particular as developed by Neurath, for understanding the tensions between science dependence and science scepticism within modern political life.