Stoicism is a philosophy, which means a general framework for navigating one’s life. It has a body of theory (e.g., the three disciplines) and a set of practices. Stoicism is just one particular philosophy of life, others include some of its Hellenistic competitors, such as Epicureanism, as well as bodies of ideas coming from outside the Western tradition, especially Buddhism. As Bill Irvine argues in his A Guide to the Stoic Life, the advantages of adopting or developing a more or less coherent philosophy of life is that one has always available a handy reminder of how to interpret things, what to prioritize, and how to behave. Not bad, if you ask me.
Epictetus, even more so than most Stoics, thought that philosophy has to be useful, or it becomes the kind of sterile intellectual exercise (some would dare say mental masturbation) that it is notorious for in certain quarters of the modern academy.
His attitude is perhaps most explicitly and fascinatingly on display in Discourses II.19, where he tackles the famous “Master Argument,” originally proposed by Diodorus Cronus in the III century BCE (i.e., about four centuries before Epictetus).
Susanne Bobzien’s chapter of the Cambridge Companion to the Stoics makes for a tough read, but it is definitely worth it for anyone seriously interested in Stoicism. It covers the basics of Stoic logic, and then some. I will only hit on some of the highlights, skipping much of the more technical details which Bobzien (rightly) gets into.
She begins by reminding her readers that Stoic logic was a type of propositional logic, concerned with what they called “assertibles,” the primary bearers of truth values. This makes perfect sense, given Stoicism’s concern with practical applications of philosophy: after all, human beings communicate by way of propositions, and the goal was to establish under what conditions what we say may or may not be truthful.