Based on a newly edited and translated Arabic version of Ptolemy’s Planetary Hypotheses, Paul Hullmeine’s study explores crucial yet often overlooked cosmological aspects of this fundamental text and shedding new light on it. The book is the published version of a doctoral thesis defended at the Ludwig-Maximilians-Universität in Munich in 2021, carried out within the Ptolemaeus Arabus et Latinus project, hosted by the Bavarian Academy of Sciences and Humanities. It adds to the growing body of works published under the PAL project since 2018, which has significantly advanced our understanding of the Arabic and Latin legacies of Ptolemaic astronomy.
The book begins with an introduction covering the history of the text, the manuscript tradition, and a discussion of editorial principles applied to both the Arabic edition and the English translation. It is followed by two analytical sections: the first examines “Astronomy, Natural Philosophy, and the Physical Reality of Celestial Bodies,” while the second focuses on “the Dynamics of Celestial Motions.” A concluding chapter synthesizes these discussions. Next come the edition and English translation of the Arabic version of the Planetary Hypotheses, along with a commentary. The annexes include two glossaries, a bibliography, and two indexes.
The Planetary Hypotheses are the main locus for Ptolemy’s cosmological theories; the work is a two-part treatise written after the Almagest. In this text, he explores several topics not addressed in his mathematical treatises: the number, shape, size, and arrangement of the celestial spheres, their motion, and the interactions between the celestial bodies and their spheres. While Ptolemy scholarship has traditionally focused on the Almagest and the mathematical aspects of astronomy, Hullmeine’s work is part of a more recent wave of studies exploring Ptolemy’s cosmology and physics.[1]
The Greek text of the treatise, which Proclus and Simplicius likely had access to in its entirety, has survived with parts of Book I and the whole Book II missing: the portion of the Planetary Hypotheses that survives in Greek represents less than a third of the complete text. However, a complete Arabic version of the treatise, produced by the ninth century, helps to restore the full text of Ptolemy’s work. Though one manuscript attributes the translation to Thābit ibn Qurra, “no clear picture about the identity of the translator has emerged” (p. 19). Until now, no complete edition of the Planetary Hypotheses in its Arabic version had been available, despite several partial editions and translations. Hullmeine’s work addresses this gap, offering a significant contribution that deserves recognition. The history of the text and its translation, as well as the challenges of a critical edition, are clearly outlined. The edition is based on three manuscripts and confirms the stemmatic relationships previously identified by Régis Morelon in 1993, when he produced an Arabic edition of Book I.[2] The new edition introduces around thirty textual variants compared to Morelon’s, all carefully documented in the critical apparatus. A second critical apparatus provides a selection of variants for the first part of Book I from the Greek version edited by Heiberg.
Hullmeine’s study not only offers an edition and translation but also examines the transition from Ptolemy’s mathematical astronomy to a cosmological theory, along with its philosophical and epistemological implications. Significant attention is given to the reception of the cosmological ideas developed in the Planetary Hypotheses within the late antique Greek tradition and to how these ideas influenced and challenged cosmology in the Islamic world. The aim is “to provide a comprehensive overview of the reception of Ptolemy’s astronomy and cosmology in general, and his Planetary Hypotheses more specifically” (p. 29).
The conceptual framework and reception history of the Planetary Hypotheses are deeply shaped by the tension between Ptolemaic astronomy and Aristotelian physics. Ptolemy rejected the idea that celestial spheres possess fixed poles that mechanically transmit motion to account for planetary movements. This interpretation, though attributed to Aristotle, may not accurately reflect his actual position; rather, it represents Ptolemy’s reading of Aristotelian thought, one that was nonetheless accepted by scholars of his time. In Ptolemy’s alternative model, celestial motion arises from certain “capacities of the soul” attributed to the planets themselves. As for the structure of celestial spheres, he examined different theories before advocating for a model in which they are not perfect spheres but rather truncated sections or sawn-off pieces. According to this model, these truncated spheres derive their motion solely from the planets to which they belong, rather than moving through any external mechanism.
The cosmological ideas Ptolemy developed carried significant astronomical, physical, and philosophical implications. Far from being universally embraced as a definitive improvement over earlier models, they sparked considerable debate. Hullmeine distinguishes different phases in the reception of the Planetary Hypotheses. In late antiquity, both Simplicius and Proclus expressed reservations about the implications of Ptolemy’s model while still recognizing its advantages over previous theories. Hullmeine’s discussion in this regard may soon be complemented by Argyro Lithari’s forthcoming study on Proclus’s Hypotyposis.[3] In the ninth and tenth centuries, discussions in the Islamic East were primarily concerned with planetary distances and sizes. By the tenth and eleventh centuries, philosophers and astronomers (including al-Fārābī, Avicenna, Ibn al-Hayṯam, and al-Bīrūnī) undertook a critical reassessment of Ptolemy’s cosmological theories, focusing on his methodological approach and the broader question of whether astronomy should be grounded in natural philosophy. Meanwhile, a distinct intellectual tradition emerged in al-Andalus, where Peripatetic philosophers such as Ibn Bāǧǧa and Averroes led what has been termed a “revolt against Ptolemaic astronomy,” in which the reading of the Planetary Hypotheses played a crucial role.
Hullmeine’s study is a robust piece of scholarship, well-documented and argued with great precision and nuance. The Planetary Hypotheses is a relatively complex and often tedious text, making it challenging to follow, but the commentary provides remarkable clarity and guidance throughout. The structure of the book leaves little room for criticism. The reader and user of the critical edition might nonetheless have preferred to find the discussion on editorial principles (pp. 22-26), particularly the description of the manuscripts used, as well as the choices regarding diagrams and critical apparatus, placed just before the edited text (pp. 221-351). The list of manuscripts cited in the book (p. 443) appears to be incomplete, as several manuscripts are not included: MS Chester Beatty Library, Dublin (Arabic 5254) (cited p. 70); MS Hyderabad, Osmania University Library, 520 RH (cited p. 110); MS Cracow, Biblioteka Jagiellońska, formerly Berlin, Staatsbibliothek, Wetzstein 87 (cited p. 112); the four Greek manuscripts cited on p. 14 are also absent from the list. Conversely, MS Berlin, Staatsbibliothek, or. quart. 1613, is mentioned in the list but does not appear elsewhere in the book. One should not underestimate the usefulness of such manuscript lists for those who contribute to online databases, as they enable more efficient cataloging and referencing.
Hullmeine opted to transliterate both Greek and Arabic terms in his book (except, of course, in the critical edition), a decision that may prove inconvenient for specialists in either language. However, this choice has its merits. By using transliteration, he ensures greater accessibility for a broader audience, including those who may not be proficient in or familiar with both scripts. This approach also facilitates cross-referencing and searching within indexes. That said, one might have wished for the Arabic script to be retained at least in the short paleographical discussion on pp. 24–25. While the choice to transliterate may not be the ideal solution for all readers, it reflects a thoughtful editorial strategy aimed at balancing scholarly rigor with usability.
In conclusion, Hullmeine’s comprehensive edition of the Arabic version of the Planetary Hypotheses will serve as an indispensable resource for scholars in the field, and his study will undoubtedly become a reference work for future research on Ptolemaic cosmology.
Notes
[1] See the works of Elizabeth Hamm, Ptolemy’s Planetary Theory: An English Translation of Book One, Part A of the “Planetary Hypotheses” with Introduction and Commentary, PhD thesis, University of Toronto, 2011; Guillaume Loizelet, Mesurer et ordonner les astres d’al-Farghānī à al-Bīrūnī: la tradition arabe du Livre des Hypothèses de Ptolémée (IXe-XIe s.), PhD thesis, Université de Paris, 2021 ; Sajjad Nikfahm-Khubravan, The Reception of Ptolemy’s Latitude Theories in Islamic Astronomy, PhD thesis, McGill University, Montreal, 2022.
[2] Régis Morelon, “La version arabe du Livre des Hypothèses de Ptolémée”, Mélanges de l’Institut Dominicain d’Études Orientales du Caire 21 (1993), 7-85.
[3] Argyro Lithari, Proclus, Hypotyposis Astronomicarum Positionum. Introduction, Text, Translation, and Commentary with a Study of the Diagrams and Illustrations, Science, Technology, and Medicine in Ancient Cultures 16, Berlin/Boston, De Gruyter, 2025.