of a difference of accent (De vocabulis quae diversum significatum exhibent secundum differentiam accentus) Commentary on Aristotle's On Generation and Corruption Commentary on Aristotle's De Anima Commentary on Aristotle's Categories Commentary on Aristotle's Prior Analytics Commentary on Aristotle's Posterior Analytics Commentary on Aristotle's Physics – Philoponus' most important commentary, in which he challenges Aristotle on time, space, void, matter and dynamics. Commentary on Aristotle's Meteorology Commentary on Nicomachus' Introduction to Arithmetic On the Eternity of the World against Proclus (De aeternitate mundi contra Proclum) On the Eternity of the World against Aristotle (De aeternitate mundi contra Aristotelem) – A refutation of Aristotle's doctrines of the fifth element and the eternity of motion and time, consisting of at least eight books. On the Creation of the World (De opificio mundi) – A theological-philosophical commentary on the Creation story in the Book of Genesis. On the Contingency of the World (De contingentia mundi) On the Use and Construction of the Astrolabe – The oldest extant Greek treatise on the astrolabe. Arbiter (Διαιτητής [Diaitêtês]) – A philosophical justification of monophysitism. Not extant in Greek; Syriac text with Latin translation. On the Trinity (De trinitate) – The main source for a reconstruction of Philoponus' trinitarian doctrine. Philosophical commentaries The commentaries of the late antiquity and early Middle Ages aimed to teach an audience. In that regard, the repetitive nature of Philoponus’ commentaries demonstrates his pedagogical awareness. Although abstract in manner, Philoponus is chiefly focused on the concept in question. Most of Philoponus’ early philosophical works strive to define the distinction between matter, extension, place, and various kinds of change. For example, the commentary On the Eternity of the World against Aristotle represents a standardized description of Aristotelian natural philosophy. Both Aristotle and Philoponus argue that in kinds of change there are differences, in their form and matter. In Physics, Aristotle operates with the idea of places, but dismisses the existence of space. The idea that came from Plato and was developed by Aristotle has been evolved by Philoponus. Philoponus attempts to combine the idea of homogeneous space with the Aristotelian system. The argument made by Philoponus is that substances by themselves require some determinate quantity for their being. Similarly to Aristotle, who rejected the immaterial things, and in contrast to Plato who accepted immaterial substances in his metaphysics, Philoponus’ concept of substance refers to the material objects. Concerning the discussion of space, Philoponus’ claim