What a scientific community holds to be its core beliefs change over time. Gilbert and Weatherall and Gilbert argue that a community’s core beliefs should be understood as a collective belief formed by a joint commitment and that these core group beliefs are difficult to change as it would require a new joint commitment to be formed. This chapter argues that the primary normative constraints on group belief revision are the weight of the evidence being considered by the group, and not the normative constraints that arise from joint commitments. This chapter sketches a positive view of how epistemic groups may respond to new evidence by looking to Kuhn’s own account of how crises arise and are resolved in science.