More background on Stoicism from the Ecole Initiative.
What I'm trying to do here is to counter my education that classical philosophy peaked with Plato and Aristotle, degenerated into the popular "feel good" philosophy of the Hellenistic period, and did not approach its earlier glory again until Plotinus. Oh, genuine and proper philosophy not returning until Descartes and Locke. You all know the rest of the narrative.
The latter Stoics of the Hellenistic period, including Cleanthes of Assos (c 331-233 BCE) and Chrysippus (c 281-208 BCE), developed Stoicism as a systematic body of doctrine, complete with a system of logic, epistemology, and cosmology. In logic, the Stoics developed the logic of propositions more recently formalized by Frege and Bertrand Russell. Chrysippus was recognized by his contemporaries as the equal of Aristotle in logic. Stoic epistemology was decidedly empiricist and nominalist in spirit. They rejected both Plato's and Aristotle's notions of form. There are no abstract universals, either apart from particulars, as Plato would have it, or in particular substances, as Aristotle held. Only particular things exist and our knowledge of them is based on the impressions they make upon the soul. Our knowledge of particular objects is therefore based on sense perception, as is our knowledge of our mental states and activities, our soul itself being a material thing.
Metaphysically, the Stoics were materialists. While all that exists is material, nevertheless there are two principles of reality. The passive principle is matter devoid of quality. Borrowing from Heraclitus, the Stoics identified the active principle of reality with the Logos, Reason, or God. Unlike later Christian versions, the Stoic view of the Logos is both materialistic and pantheistic. God has no existence distinct from the rational order of nature and should not be construed as a personal, transcendent deity of the sort essential to later Western theism.
The Stoics were determinists, even fatalists, holding that whatever happens happens necessarily. Not only is the world such that all events are determined by prior events, but the universe is a perfect, rational whole. For all their interests in logic and speculative philosophy, the primary focus of Stoicism is practical and ethical. Knowledge of nature is of instrumental value only. Its value is entirely determined by its role in fostering the life of virtue understood as living in accord with nature.
My attraction is practical ethical side of Stoicism to its conception of ethical philosophy as the art of living well. Stoicism, like its rival Epicureanism, addressed the questions that most people are concerned with (death, suffering, great wealth, poverty, power over others and oppression) in very direct and practical ways.
The Stanford Encyclopedia says:
"The Stoics claim that whatever is good must benefit its possessor under all circumstances. But there are situations in which it is not to my benefit to be healthy or wealthy. (We may imagine that if I had money I would spend it on heroin which would not benefit me.) Thus, things like money are simply not good, in spite of how nearly everyone speaks, and the Stoics call them ‘indifferents’ (Diog. Laert., 58A)--i.e., neither good nor bad. The only things that are good are the characteristic excellences or virtues of human beings (or of human minds): prudence or wisdom, justice, courage and moderation, and other related qualities.These are the first two of the ‘Stoic paradoxes’ discussed by Cicero in his short work of that title: that only what is noble or fine or morally good (kalon) is good at all, and that the possession (and exercise) of the virtues is both necessary and sufficient for happiness. But the Stoics are not such lovers of paradox that they are willing to say that my preference for wealth over poverty in most circumstances is utterly groundless. They draw a distinction between what is good and things which have value (axia). Some indifferent things, like health or wealth, have value and therefore are to be preferred, even if they are not good, because they are typically appropriate, fitting or suitable (oikeion) for us."