 The Stoics are materialists, and they believe that every action we perform is causally determined by god as part of his divine plan. This might seem to make us helpless puppets of god, puppets who cannot rightly be held responsible for what we do. The Stoics, however, develop a theory of animal behavior generally and human action in particular that tries to counter this suspicion. Like both Aristotle and Epicurus, for the Stoics, the possession of reason is key to making humans responsible for their actions.