Abstract: Current accounts of normativity struggle to explain the source of the normative grip of rationality norms. They fail to explain, that is, why one should be committed to adhering to rationality norms rather than to violating them, or why one should be guided by rationality norms at all. A popular fix is to appeal to a constitutive account of agency: the normative grip of rationality norms can be found in constitutive features of agency, such as beliefs, desires or drives. If accepting rationality norms is constitutive of this feature of agency, then, in virtue of being an agent, we are guided by rationality norms. This is one promising way to pin down the source of the normative grip of rationality norms. The problem, I argue in th...