Posidonian Psychology in Galen’s De placitis Hippocratis et Platonis

My project at the Center for Hellenic Studies was devoted to the study of Stoic theories of passion and, in particular, to the role of Posidonius in reshaping Stoic moral psychology. The work carried out during my fellowship constitutes a substantial portion of my forthcoming monograph, Posidonian Psychology in Galen’s De placitis Hippocratis et Platonis (Brill), which seeks to reassess Posidonius’ place in the development of Stoic thought on emotion.

The project is guided by a simple but central question: how did the Stoics conceptualize passion (pathos), and how did this conception evolve from the system of Chrysippus to the modifications introduced by Posidonius? The answer is not straightforward, as the evidence is dispersed across a wide range of sources, many of them polemical in nature and transmitted by authors with their own philosophical agendas. Nevertheless, the question is of fundamental importance for understanding Stoic ethics since passions were regarded as the primary obstacle to living in accordance with nature.

During my time at the CHS, I was able to draft one-and-a-half chapters of the book. The first of these chapters reconstructs Chrysippus’ theory of passion, which became the canonical Stoic position and was defended against rival schools throughout the Hellenistic period. According to Chrysippus, passions are not the result of a conflict among irrational parts of the soul but rather erroneous judgments about value: they arise when the subject assents to the false impression that something (that is not a good) is a genuine good. On this account, passions are not external forces that overpower reason; rather, they are reason itself—an excessive impulse of reason that disobeys itself.

The second major portion of my work, which I was able to advance considerably during the fellowship, concerns the second chapter, devoted to the presentation of Posidonius, his method, and the particular interest that Galen took in him. The part of the chapter already written offers an introduction to Posidonius, his philosophical training, and his concern with the use of scientific method and the search for causes. This aspect was especially appreciated by Galen, who recognized in Posidonius a methodological affinity with his own scientific outlook. Indeed, Galen is the other central figure of the book, since it is thanks to him and to his De placitis Hippocratis et Platonis that Posidonius’ thought can be reconstructed and his relationship to earlier Stoics assessed. The problem with the PHP is that Galen presents Posidonius as a Platonist in disagreement with orthodox Stoic theory—an interpretation that I aim to challenge in the chapters still in progress. Galen depicts him as an ally in refuting Chrysippus’ monistic account of the soul, embracing instead the Platonic view according to which human psychology cannot be explained solely in terms of rational assent but must also include elements akin to the irrational parts of the soul.

The work carried out at the CHS was crucial for clarifying the methodological challenges posed by the sources. Galen’s polemical aims in the PHP complicate the reconstruction of Posidonius’ authentic position: Galen quotes selectively, paraphrases freely, and at times seems to exaggerate the distance between Chrysippus and Posidonius in order to strengthen his own arguments against Stoic monism. At the CHS I was able to examine this problem closely, comparing Galen’s testimony with other fragments of Posidonius and with the broader Stoic tradition. This careful cross-analysis allowed me to distinguish, as far as the evidence allows, between Galen’s voice and Posidonius’ own contribution.

The CHS provided the ideal environment for advancing this stage of the book. The library resources enabled me to engage systematically with both ancient sources and the considerable body of modern scholarship on Stoic psychology, Galen’s polemics, and the fragmentary evidence for Posidonius. Equally important were the opportunities for discussion with colleagues and fellows working on related topics in philosophy, history, and classical literature. These conversations helped refine my arguments and situate my project within broader scholarly debates. In addition, the librarians were immensely supportive, creating a welcoming atmosphere and providing the best possible conditions for focused research.

By the end of my fellowship, I had completed a full draft of the chapter on Chrysippus’ theory of passion and a substantial portion of the chapter devoted to Posidonius’ methodology. This progress represents an essential step toward the completion of the monograph, which will offer a comprehensive analysis of Posidonius’ contribution to Stoic theories of passion. My hope is that this work will shed new light on the complexity of Stoic moral psychology and, above all, on the figure of Posidonius—restoring him to view as a Stoic thinker rather than, as Galen and much of the secondary literature would have it, a Platonist.