Summary of doctoral thesis:Prohairesis, or decision, plays a central role in the ethical theory Aristotle develops in the Nicomachean Ethics. In NE VII.8, it is the feature whose presence or absence distinguishes base action done viciously from base action done akratically. Further, it plays a vital role in the definition of character excellence in NE II.6 and of practical truth in NE VI.2. Should we fail to properly define Aristotelian prohairesis, we will struggle to fully grasp several of the most fundamental theses of the NE. The greatest impediment to progress on such a definition is that Aristotle appears to deploy this term and its variants along differing conceptual extensions. In my doctoral work, I aim to determine whether after all Aristotle has a unified account of prohairesis. In approaching this general goal, I am tasked first with explaining the precise relation obtaining between different kinds of prohairesis across NE. Towards accomplishing both this subsidiary aim and the primary goal of my project, I will engage in extensive analysis of the Nicomachean Ethics, Eudemian Ethics, and Magna Moralia.