 In his discussion of responsibility in A System of Logic (SL VI.ii.1–4) Mill suggests that he thinks that humans are responsible agents and that this is what marks us as progressive beings. There he claims that capacities for practical deliberation are necessary for responsibility. In particular, he claims that moral responsibility involves a kind of self-mastery or self-governance in which one can can deliberate about the appropriateness of one’s desires and regulate one’s actions according to these deliberations (SL VI.ii.3). If this is right, then Mill can claim that possession and use of our deliberative capacities mark us as progressive beings, because they are what mark as moral agents who are responsible. If our happiness should reflect the sort of beings we are, Mill can argue that higher activities that exercise these deliberative capacities form the principal or most important ingredient in human happiness.