Cleanthes of Assos, who succeeded Zeno as head of the school, is best known for his Hymn to Zeus, which movingly describes Stoic reverence for the cosmic order and the power of universal reason and law. The third head of the school, Chrysippus of Soli, who lived to the end of the 3rd century, was perhaps the greatest and certainly the most productive of the early Stoics. He devoted his considerable energies to the almost complete development of the Zenonian themes in logic, physics, and ethics. In logic particularly, he defended against the Megarian logicians and the Skeptics such concepts as certain knowledge, comprehensive presentation, proposition and argument, truth and its criterion, and assent. His work in propositional logic, in which unanalyzed propositions joined by connectives are studied, made important contributions to the history of ancient logic and was of particular relevance to modern developments in logic.
In physics, Chrysippus was responsible for the attempt to show that fate and free will are not mutually exclusive conceptual features of Stoic doctrine. He further distinguished between “whole” and “all,” or “universe,” arguing that the whole is the world, while the all is the external void together with the world. Zeno’s view of the origin of human beings as providentially generated by “fiery reason” out of matter was expanded by Chrysippus to include the concept of self-preservation, which governs all living things. Another earlier view (Zeno’s), that of nature as a model for life, was amplified first by Cleanthes and then by Chrysippus. The Zenonian appeal to life “according to nature” had evidently been left vague, because to Cleanthes it seemed necessary to speak of life in accord with nature conceived as the world at large (the cosmos), whereas Chrysippus distinguished between world nature and human nature. Thus, to do good is to act in accord with both human and universal nature. Chrysippus also expanded the Stoic view that seminal reasons (germinal principles) were the impetus for motion in living things.
He established firmly that logic and (especially) physics are necessary and are means for the differentiation of goods and evils. Thus, a knowledge of physics (or theology) is required before an ethics can be formulated. Indeed, physics and logic find their value chiefly in this very purpose. Chrysippus covered almost every feature of Stoic doctrine and treated each so thoroughly that the essential features of the school were to change relatively little after his time. Later Roman Stoicism
The Middle Stoa, which flourished in the 2nd and early 1st centuries bce, was dominated chiefly by two philosophers of Rhodes: Panaetius, its founder, and his disciple Poseidonius. Panaetius organized a Stoic school in Rome before returning to Athens, and Poseidonius was largely responsible for an emphasis on the religious features of the doctrine. Both were antagonistic to the ethical doctrines of Chrysippus, who, they believed, had strayed too far from the Platonic and Aristotelian roots of Stoicism. It may have been because of the considerable time that Panaetius and Poseidonius lived in Rome that the Stoa there turned so much of its emphasis to the moral and religious themes within the Stoic doctrine. Panaetius was highly regarded by Cicero, who used him as a model for his own work. Poseidonius, who had been a disciple of Panaetius in Athens, taught Cicero at his school at Rhodes and later went to Rome and remained there for a time with Cicero. If Poseidonius admired Plato and Aristotle, he was particularly interested—unlike most of his school—in the study of natural and providential phenomena. In presenting the Stoic system in the second book of De natura deorum (45 bce; On the Nature of the Gods), Cicero most probably followed Poseidonius. Because his master, Panaetius, was chiefly concerned with concepts of duty and obligation, it was his studies that served as a model for the De officiis (44 bce; On Duties) of Cicero. Hecaton, another of Panaetius’s students and an active Stoic philosopher, also stressed similar ethical themes.
Cicero, Marcus TulliusMarcus Tullius Cicero, detail of a marble bust; in the Capitoline Museums, Rome.© AISA—Everett/Shutterstock.com
If Chrysippus is to be commended for his diligence in defending Stoic logic and epistemology against the Skepticism of the New Academy (3rd–2nd century bce), it was chiefly Panaetius and Poseidonius who were responsible for the widespread popularity of Stoicism in Rome. It was precisely their turning of doctrine to themes in moral philosophy and natural science that appealed to the intensely practical Romans. The times perhaps demanded such interests, and with them Stoicism was to become predominantly a philosophy for the individual, showing how—given the vicissitudes of life—one might be stoical. Law, world citizenship, nature, and the benevolent workings of providence and the divine reason were the principal areas of interest of Stoicism at this time.
Such tendencies toward practicality are also well illustrated in the later period of the school (in the first two centuries ce) in the writings of Lucius Seneca, a Roman statesman; of Epictetus, a former slave; and of Marcus Aurelius, a Roman emperor. Both style and content in Seneca’s Libri morales (Moral Essays) and Epistulae morales (Moral Letters) reinforce the new direction in Stoic thought. The Encheiridion (Manual) of Epictetus and the Meditations of Marcus Aurelius furthered the sublime and yet personal consolation of the Stoic message and increasingly showed the strength of its rivalry to the burgeoning power of the new Christianity. The mark of a guide, of the religious teacher, is preeminent in these writings. It is difficult to establish with any precision, however, the extent of Stoic influence by the time of the first half of the 2nd century ce. So popular had these ideas become that many specifically Stoic terms (viz., right reason, comprehension, assent, indifference, logos, and natural law), as well as the notion of the wise person, were commonly used in debate and intellectual disputes.
Marcus AureliusBronze equestrian statue of Marcus Aurelius, erected c. 173 ce; in the Piazza del Campidoglio, Rome.Alinari—Art Resource/Encyclopædia Britannica, Inc.
Stoic elements in Pauline and patristic thought
There is much disagreement as to the measure of Stoic influence on the writings of St. Paul the Apostle. At Tarsus, Paul certainly had opportunities for hearing Stoic lectures on philosophy. And it may be that his discussion of nature and the teaching of it (1 Corinthians 11:14) is Stoic in origin, for it has a parallel in the Manual of Epictetus (1.16, 10). Although not a Stoic technical term, syneidēsis, which Paul used as “conscience,” was generally employed by Stoic philosophers. In 1 Corinthians 13 and in the report of Paul’s speech at Athens (Acts 17), there is much that is Hellenistic, more than a little tinged by Stoic elements—e.g., the arguments concerning the natural belief in God and the belief that human existence is in God.