Another way I would express today my view of this is that the Platonist/Aristotelian/Stoic side maintains that there is something symbolized by the word "good" that can be decoded by use of formal logic and formal reason, based on abstractions such as "A" and "B," to determine how to live, and that these decisions cannot be made absent a reduction of these symbols (like the "good") into a logical formula that is universally applicable.
That's because on an even deeper level they do not accept that any assertion an be proved as true unless it is reducible into such a formula.
As support for my analysis here I would cite a line from DeLacy's commentary to "On Methods of Inference" that has been burned into my mind since I first read it.