Category: Persons

Panaetius & Posidonius

Stoic philosophers who studied and incorporated in their philosophical system Platonic and Aristotelian doctrines.

Middle Stoicism

The period of Stoicism that covers the second and first century BCE is often called ‘Middle Stoicism’ and it is characterized as the Platonic phase of Stoic philosophy. During this period the most important Stoics were Panaetius and Posidonius, who got interested in Plato’s philosophy both because they admired Plato and because they thought that in this way they would be able to rebut more successfully the criticism of the Academic Sceptics.


Panaetius (185/180 BCE - 110/109 BCE) came from Rhodes, studied in Athens with the Stoic philosophers Diogenes of Babylon and Antipater from Tarsus, went to Rome where he taught philosophy, and after Scipio’s death (129 BCE) he returned to Athens and succeeded Antipater as the head of the Stoic school.

His most well-known work, the Περὶ τοῦ καθήκοντος, has not survived, but it formed the basis for Cicero’s first two books of De officiis. From Cicero’s work, which deals with the apparent conflict between what is virtuous and what is beneficial, it becomes clear that Panaetius tried to moderate the utopian character of Stoic ethics, which distinguishes in an absolute way the actions of the wise man from those of the fool. Panaetius stressed the possibility of moral progress for all those who are not wise but perform proper actions (καθήκοντα), even if their actions are not based on the perfect knowledge that only the wise man has (κατορθώματα). For this reason, Panaetius recognized and recommended the help of general moral rules, which Cicero later elaborated and adapted to the conditions of the Roman society.

Panaetius was not concerned with logic, but he was interested in natural philosophy and seems to have disagreed with the standard Stoic dogma on three topics: he denied the periodical conflagration of the world (ἐκπύρωσις), he was against astrology and divination, and he was influenced by Plato and Aristotle concerning the bipartite division of the soul into the rational and non-rational part. Indeed, his attempt to present Stoicism as a continuation of Socrates’ teaching led him to doubt the historical accuracy of Plato’s Phaedo, in which Socrates advocates the immortality of the soul, a doctrine that does not accord with the Stoic views.


Posidonius (approx. 135 BCE – 51 BCE) came from Apameia, he was a student of Panaetius in Athens, and around 95 BCE he moved to Rhodes where he took on multiple high offices. He thus had the possibility to travel to many places in the Mediterranean that were part of the Roman state and outside of it. This greatly helped him to collect data that constituted the basis for his studies in astronomy, geography, meteorology, ethnography and history. His encyclopaedic knowledge as well as his philosophical works exhibit the signs of Plato’s and Aristotle’s influence to a greater extent than in Panaetius’ case.

Posidonius was interested in logic and most probably introduced a new kind of syllogism, which Galen later called syllogisms κατὰ τὸ πρός τι; for instance: A is double than B. B is double than C. Therefore A is four times bigger than C. In natural philosophy he developed the notion of συμπάθεια, i.e. of the interdependence and interconnection of the cosmic and sublunar phenomena, including the human behaviour; in this way he laid the theoretical foundations for the justification of astrology and divination. Also, in contrast to the other Stoics, he became interested in mathematics and wrote a whole treatise in order to defend its axiomatic character.

Posidonius’ most important innovation can be found in ethics, and in particular in his theory about the soul. He criticized Chrysippus’ monistic psychology and followed Plato in his tripartite division of the soul. Nevertheless, he did not reject the Stoic position according to which human emotions and desires (πάθη) are functions of the rational soul and represent beliefs about what we should pursue and what we should avoid. Indeed, he claimed that the soul has two kinds of capacities (παθητικαὶ κινήσεις), which urge us to act and are not governed by the rational soul. These capacities, Posidonius said, do not belong to non-rational parts of the soul, as Plato and Aristotle had previously argued, but are independent and should be considered as belonging to the rational soul.So, it seems that the role that Posidonius attributed to them in the context of Stoic ethics is comparable to the role of the Platonic and the Aristotelian ἐπιθυμία and θυμός of the non-rational parts of the soul.

According to Posidonius, therefore, the nature of the soul explains adequately human behaviour and the way by which we can try to improve it. Since our emotions and desires emerge from the cooperation of our rational soul and its non-rational capacities, we become virtuous when we possess perfect knowledge as well as when we exercise these capacities, for instance, with poetry and music. In other words, knowledge is not sufficient to control our emotions and desires, and hence it is not simply up to knowledge whether we can live a virtuous life. But such a position is not exactly in accordance with Stoic ethics and has perceived as distancing Posidonius from the Stoic dogma.

However, Posidonius himself seems to have thought that with his theory about the soul he was interpreting the views expressed by Zeno and Cleanthes more closely than Chrysippus had done before him. For his aim was to reconnect Stoic philosophy with its Platonic heritage. In fact, it has been suggested that the dialogue which mainly influenced him was the Timaeus, in which this theory is attributed to Timaeus, who was a Pythagorean, and Stoic psychology was thus presented as the extension of an old and respectable philosophical tradition, Pythagorianism. It is hence important to underline that Posidonius did not suggest his theory about the soul in order to overthrow Stoic philosophy. And the same holds for his other innovations as well as for those of his teacher Panaetius. That is to say, they both were mainly interested to enrich Stoic philosophy with theories from the previous philosophical schools that were mostly in agreement with the spirit of Stoicism and did not contradict it.

Author: Katerina Ierodiakonou
  • Alesse, F. Panezio di Rodi: Testimonianze. Naples, 1997.
  • Cooper, J. "Posidonius on emotions." Sihvola, J., Engberg-Pedersen, T. eds. The Emotions in Hellenistic Philosophy. Dordrecht, 1998.
  • Kidd, Ιan , Edelstein, L. Posidonius I: The Fragments. Cambridge, 1972.
  • Kidd, Ιan. Posidonius II: The Commentary 2 vols.. Cambridge, 1988.
  • Sedely, D. "The school, from Zeno to Arius Didumus." Inwood, B. ed. The Cambridge Companion to the Stoics. Cambridge, 2003.
  • Long, A.A. Hellenistic philosophy. London, 1974.
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