What is extremism, and how can it be countered? According to a recent account by (Cassam, 2021), there are three kinds of extremism: ideological, methodological, and psychological. The psychological kind – what Cassam calls ‘mindset extremism’ – is used by Cassam to explain what leads individuals to resort to extreme methods. From there we can say that methods extremism can be countered by preventing people from becoming mindset extremists. This paper outlines Cassam’s overall theory, and challenges it in two respects. (...) First, it is argued that whilst mindset extremism does account for some individuals, it applies more readily to groups in a way analogous to the contrast between individual and group belief. This creates space for an account of group mindset extremism. Second, I propose that Cassam’s account of the role mindset extremism occupies in predicting an individual’s turn to extreme methods underplays the social aspects that lead the individual to form the mindset. By acknowledging these social and group properties, we can begin to develop a social epistemology of extremism. (shrink)