[NB: This is the third in a series of posts about Book VI of the Nicomachean Ethics. I explain the project in Part 1.]
I claimed in Part 2 that EN VI is structured around a search for the kind of reason that explains how we can go about correctly choosing the mean, that is, making the right ethical choice. As Aristotle points out in the first half of VI.2, reasoning of this sort belongs to the more general category of reasoning about contingent things, which is the province of the faculty for calculation, to logistikon (1139a3-15).
Not all calculation is about ethical matters, of course, since calculation is also present in crafts such as medicine. It’s perhaps worth noting here that I don’t think Aristotle is committed to the thought that all ethical reasoning is calculative, either. We might think that the theoretical enterprise of the ethical works themselves is also a form of reasoning, namely, inquiry. And ethical inquiry is not calculative since it is not directed in the first instance toward what is contingent, that is, the sphere of particular and determinate actions, although it certainly seeks to shape our calculative reasoning.
Aristotle is in quite direct conversation with Plato throughout this passage, even deploying the familiar argument from Republic V that cognitive states are distinguished according to the ontological status of their objects, in order to distinguish the faculty for scientific knowledge (to epistêmonikon), whose objects are necessary, from that for calculation (1139a6-11). There’s another interesting connection to Plato in Aristotle’s use of logistikon to denote the sphere to which the reasoning that leads to correct choice belongs.