 This is the logical part, which finds reasons, shows what is a reason, and that a given reason is a correct one.This last part is necessary, but only on account of the second, which again is rendered necessary by the first.Both the "Discourses" and the "Enchiridion" begin by distinguishing between those things in our power ("prohairetic" things) and those things not in our power ("aprohairetic" things).