This chapter concerns the connection between knowledge of a logical principle, such as Modus Ponens, and actions of reasoning with it. Contemporary discussions of this issue typically mention Lewis Carroll’s regress. There is widespread agreement that the regress shows something important about the connection between knowing logical principles and reasoning with them—and, more generally, between knowing epistemic or practical principles and actions involving them. My first aim is to address key interpretations of Carroll’s regress in order to assess its relevance to the question of how knowing logical principles connects to reasoning with them, and, more generally, of how knowing epistemic or practical principles might be action-guiding. My second aim is to show that the regress fails to establish anything of substance about such connections unless substantive, contentious, and typically undefended assumptions are made.