The idea that agents can be morally responsible for their actions plays a central role in human interaction. Understanding the nature of moral responsibility thus promises to give us insight into what we presuppose about human nature. Unfortunately, two crucially different aspects of moral responsibility – attributability and accountability – have not generally been distinguished. An agent is attributionally responsible for an action if and only if, at the time of action, he has control over the fact that he performs it – in other words, if and only if his action is up to him. When and only when this is so, it is appropriate to appraise him for it in terms of virtues and vices. An agent is accountable for an action if and only if it is appropriate to respond to him with reactive attitudes, such as resentment, indignation, or gratitude.

In my dissertation, I present capacity-based theories of these two aspects of moral responsibility. In particular, in Chapter 1, I argue that an agent is attributionally responsible for an action if and only if, at the time of action, he has the ability to respond to his judgments about reasons for and against that action by performing or not performing it, respectively. In Chapter 2, I argue that an agent is accountable for an action if and only if he is attributionally responsible for it and has the ability to recognize and respond to moral reasons. A straightforward connection exists between these two theories. The ability to recognize and respond to moral reasons presupposes the capacity required for attributability. Thus an agent is accountable for an action if and only if he has the capacity to recognize and respond to moral reasons.

In Chapters 3 and 4, I demonstrate that we can be morally responsible – in both senses – for our non-epistemic attitudes (e.g., desires and intentions). I then show that my theories from the previous two chapters readily extend to account for this.

Finally, in Chapter 5, I argue against Stephen Darwall's recent and influential theory of accountability, thereby showing that it poses no challenge to mine.