 Whether Aristotle’s theory of what is voluntary is compatibilist or incompatibilist with regard to causal determinism is highly contested. But the question itself may be misguided, as Aristotle never formulates the thesis of causal determinism or asks whether determinism is compatible with people engaging in voluntary actions. The best we can do is ask whether, given his other philosophical commitments, Aristotle’s conditions on voluntary action are best understood as compatible with determinism, or incompatible with it. Some contemporary philosophers believe that causal determinism is incompatible with an agent genuinely being the source of his action, as his action could be traced back to environmental, genetic, and other factors outside of and prior to the agent. But Aristotle seems not to be working with that strong a notion of sourcehood when he says that the agent is the origin of his actions: he says that choice is origin of action, while desire and practical reason are the origin of choice (NE 6.2 1139a32–33). So Y can be the origin of Z, while Y itself has an origin in X. Likewise, many philosophers believe that PAP is incompatible with causal determinism, while others believe that they are compatible. Aristotle himself is silent on the issue, and he never produces an explication of what exactly he means when he says an agent who acts voluntarily could have done otherwise. However, he does think that virtue is a perfection of a person’s character, one that reliably produces virtuous actions. The virtuous person has both correct beliefs about what to do, and correct desires, so he would seem to have no motive to do anything other than the right thing, and Aristotle does say that the virtuous person would never voluntarily do anything vicious (NE 4.9 1128b25–30). So it seems that, while the virtuous person who voluntarily performs a virtuous action could have acted otherwise and done something vicious, nonetheless there are sufficient conditions—ones that include his own virtue—which preclude him from exercising this ability. While opinions on the question are divided, perhaps the safest thing to say is that Aristotle’s theory is compatible with compatibilism. (See Destrée (2011) for an incompatibilist interpretation of Aristotle based on ‘sourcehood’ and Aristotle’s acceptance of PAP, and Bobzien (2014) for criticisms. Meyer (2011) gives an interpretation on which Aristotle’s theory of voluntary action and of character formation is compatible with compatibilism.)