Personal Agency consists of two parts. In Part II, a radically libertarian theory of action is defended which combines aspects of agent causalism and volitionism. This theory accords to volitions the status of basic mental actions, maintaining that these are spontaneous exercises of the will--a 'two-way' power which rational agents can freely exercise in the light of reason. Lowe contends that substances, not events, are the causal source of all change in the world--with rational, free agents like ourselves having a special place in the causal order as unmoved movers, or initiators of new causal chains. And he defends a thoroughgoing externalism regarding reasons for action, holding these to be mind-independent worldly entities rather than the beliefs and desires of agents. Part I prepares the ground for this theory by undermining the threat presented to it by physicalism. It does this by challenging the causal closure argument for physicalism in all of its forms and by showing that a dualistic philosophy of mind--one which holds that human mental states and their subjects cannot be identified with bodily states and human bodies respectively--is both metaphysically coherent and entirely consistent with known empirical facts.