The major Stoic philosophers were Zeno of Citium (Cyprus), who lived between 336 and 265 BCE, Cleanthes (c. 331-232 BCE) and Chrysippus (c. 280-206 BCE), both from Asia Minor. Later Stoics of the Christian era include Seneca (c. 4 BCE-65 CE), Epictetus (c. 50-138 CE), and Emperor Marcus Aurelius (121-180 CE). Epicurus (341-270 BCE) was born on Samos, and although his parents were Athenians his early education was received in Asia Minor from teachers versed in the philosophies of Plato and Democritus. His most famous spiritual descendant was the poet Lucretius (99-55 BCE), whose De Rerum Natum set to verse the tenets of Epicurean thought.
Stoicism and Epicureanism are rival philosophies, but they shared several characteristics of note, especially in their early development. Both were responses to the influential schools of the Cynics and Skeptics, responses designed to restore philosophy to respectability. Although Stoicism never matched the radical materialism of the Epicureans, both systems adopted a naturalistic perspective. Both also were spare in their ontologies, committed to the view that the universe is ultimately reducible to a single agency, force, element, or kind of “stuff.” For the Epicurean it was atomic; for the early Stoics, something akin to ire or ether. The Stoics often referred to this “creative fire” as Logos and thought of the divine in the same physicalistic terms.
Perhaps the chief contribution of Stoic psychology was in the stress laid on the importance of language. The later Stoics especially regarded human linguistic prowess as effectively establishing a unique place and family from which all non-linguists were forever excluded. Thus did the Stoics begin the tradition of regarding human beings as specially endowed with rights otherwise unavailable outside the human family. Central to Stoic thought is an ethics of rationality made possible by language—an ethics pitting rationality against emotion. Even the word pathos, which might generally be taken to refer to a passion or emotion, was generally intended within Stoic contexts to be regarded as a kind of disease of the soul or something on the way toward psychopathology, the cure for which was apatheia, the utter elimination of passions and emotions that would oppose or resist the authority of reason. It is with Stoicism that the ageless tension between rationality and emotionality is eliminated with the renunciation of emotion itself.
Epicurean psychology was more materialistic, associationistic, and sense-based. Experience is recorded in memory and can be revived in the form of concepts. By association, these concepts come to stand for the items originally given in experience. Frequent pairings of an actual apple with the word apple results in the expectation (prolepsis) of an apple when the word is heard. Since the only mode of verification is experience itself, questions regarding the truth or validity of experience are meaningless. All experience is the outcome of interactions (collisions) between material entities, the matter of the world and the matter of the sense organs. Random collisions can produce random outcomes, as disease can produce pathological outcomes. Nevertheless, the properly functioning sense organ responds to what is there. The soul itself is a type of material organization made up of common elements, fire, wind, and air, and a fourth unnamed element that makes it possible for stimulation to be distributed over and within the body. This last element is the most subtle but is material nonetheless. As a result of its activity, however, there arises the capacity for pleasure and for pain. The business of life—the very preservation of life—centers on these facts and functions.