It has occurred to me that there is an apparent flaw in the otherwise perfect logic of Stoicism. Stoicism defines Virtue as the only real good - as the Good, in fact. According to the Stoics, only decisions to act in accord with Virtue can be good, and nothing else is. Decisions to act in opposition to Virtue are the only Evil, and everything else is indifferent, although according to some Stoics, we may distinguish between "preferred" and "dispreferred" indifferents.
So the non-sage may think that money, or possessions, or good health, or long life are good things. But they are not; they are indifferent (though we may prefer them to the alternatives). Only things that enter the sphere of moral action can be good or evil.
The apparent flaw? Well . . . what is Virtue? It is fine to say, "Only acting with Virtue is Good," but one must know what that means. Do the Stoics?
Interestingly, I don't know of a single place where a Stoic author defines what is and is not Virtue, not definitively. It almost seems like the famous "definition" of "pornography" - "I don't know what it is, but I know it when I see it!" But I think there are clues to the thought of the ancient Stoics.
For one thing, the Stoics often speak of and seem to take for granted the "four cardinal virtues" - Wisdom (Sophia), Courage (Andreia), Justice (Dikaiosyne), and Temperance (Sophrosyne). In some places, these seem to be synonymous with the Virtue, in other places, they are simply spoken of as if they were "part of" Virtue, or contribute to it somehow. But even these may seem vague, anyway. What, after all, is Wisdom? Or Courage? Or Justice, or Temperance?
I think another clue is to be found in the fact that the Stoics, like virtually every school of ancient philosophy, considered themselves to be the intellectual heirs of Socrates. I think they have a better claim to it than most. The important point here is that Socrates would never have given a final definition of any of these virtues, nor of Virtue. He would be perpetually seeking it through Reason. So many of his discussions, as Plato depicts them, begin with him asking someone who considers himself an expert, "So, what is 'Courage,' anyway?" The purpose of the dialogue is to expand and refine that definition, to seek its heart, to understand it better . . . and to always keep asking, rather than to settle for a fixed definition. Plato would later depict Socrates as believing in absolute fixed "Forms" of concepts like "Courage," but it seems totally out of character from what we know of Socrates, the eternal questioner, that he would accept that anyone living could really know it. Only by philosophy - only by asking questions - can we even approach the Truth. And I rather think this might be part of the "missing" component of Stoic thought on Virtue - that while it may (or may not be) a fixed and eternal Truth, we cannot perfectly know it, and are obliged to keep considering it, questioning it, and learning it.
Other than this, say the Stoics, Virtue consists in knowing the difference between what you can control and what you cannot, accepting that which you cannot change, and doing your best to use your faculty of moral choice for those things you can.
These are just some thoughts, not necessarily as coherent as I would like, on the topic. I may have to expand this more at a later time . . .