I develop here a Kantian framework for understanding conscience in order to examine whether moral flaws of psychopaths are traceable to their dysfunctional conscience. When understood as the reflective capacity for moral self-assessment that triggers certain emotional reactions, conscience proves to be a fruitful tool for explaining psychopathic moral incompetence. First, I show how the unrealistic moral self-assessment of psychopaths affects their competence in judging moral issues and in being motivated to act morally. I then highlight how focusing on this specific rational deficit of psychopaths significantly modifies the status of rationalism within the contemporary dispute as to whether psychopathy supports sentimentalism exclusively