Aristotle and the necessity of habituation: re-reading Nicomachean Ethics 2.4

In Nicomachean Ethics 2.4 Aristotle raises a puzzle about moral habituation. Scholars take the puzzle to concern how a learner could perform virtuous actions, given the assumption that virtue is prior to virtuous action. I argue, instead, that Aristotle is concerned to defend the necessity of practice, given the assumption that virtue is reducible to virtuous action.