action theory, subfield of philosophy of mind that is specially important for ethics; it concerns the distinction between things that happen to a person and things one does or makes happen. Action theorists consider issues such as motive, desire, purpose, deliberation, decision, intention, trying, and free will. A central problem is the question of volition, or what connects intention with bodily movement; in Ludwig Wittgenstein’s formulation, “What is left over if I subtract the fact that my arm goes up from the fact that I raise my arm?”