Deriving The Cardinal Virtues In Cicero's On Duties

Two questions came up recently about Stoicism and the virtues in one of my social media feeds.  How did they end up with those four main virtues - Wisdom, Justice, Courage, and Temperance - and do they provide any argument or rational proof for those being the main virtues?

Quite likely, more complete responses to these questions would be found in some of the Stoic literature that has unfortunately been lost.  But we do still have some more or less complete answers provided in some o...