The paper analyses Averroes's and Aquinas's different reconstructions of Aristotle's ontology in the central books of the Metaphysics. The main claim the paper argues for is that Averroes endorses an explanatory criterion of substantiality, while Aquinas favours an independent existence criterion. The result of these different choices is that the Arabic commentator believes that the forms of sensible objects are more substances than the objects of which they are the forms, while the Dominican Master sticks to the traditional picture that sensible objects hold some kind of priority over their ontological constituents in general and over form in particular. For Averroes, therefore, the central books of the Metaphysics mark a major departure from the Categories ontology, where particular sensible objects are regarded as fundamental entities and so primary substances. On Aquinas's reconstruction, by contrast, sensible objects are still thought of in the Metaphysics as primary substances in spite of their being analysable into matter and form.

In order to get rid of the contradictions he had identified in Ptolemy’s Astronomy, Ibn al-Haytham abandons cosmology and develops a purely kinematic description of the movement of the wandering stars. This description culminates with the proof that such a star, during its daily movement, reaches exactly one time a maximum height above the horizon and that any inferior height is reached exactly twice. The proofs of these facts necessitates new mathematical tools and Ibn al-Haytham is led to establish very sophisticated statements concerning the variation of certain ratios of arcs of circles on the sphere. He also introduces the fruitful idea of assimilating a very small spherical triangle to a plane triangle.

The present article aims to provide a reconstruction of the interpretation offered by Thomas Aquinas of the cognitive process described at the beginning of Aristotle's Physics and of his criticism of Averroes' interpretation. It expounds to this end the exegesis of ancient Greek commentators who opened the debate on this question; then, it puts forward a reconstruction of Aquinas' doctrine by means of other texts of his corpus, as well as an explanation of his criticism of Averroes' exegesis; it finally reconstructs Averroes' interpretation worked out in his Great Commentary to Phys. I, 1, in order to show that Aquinas' disapproval is partly due to an incorrect interpretation of Averroes' divisio textus of Phys. I, 1. It suggests as well that, concerning some fundamental points, Aquinas' exegesis doesn't diverge from the interpretation proposed by Averroes.

The present article aims to show that the treatise On the Harmonization of the Opinions of the Two Sages the Divine Plato and Aristotle cannot have been written by al-Fārābī. It considers to this end four crucial issues treated in this work, concerning (1) divine Providence and the particulars, (2) Platonic Ideas and the divine Intellect, (3) creation ex nihilo and (4) the divine attribute of ‘will’. It establishes in each case that the thesis defended by the author is contrary to al-Fārābī’s doctrine and akin to that of Yaḥyā ibn ‘Adī. This twofold result prompts us to suggest that the author should be associated with Ibn ‘Adī and his milieu; it also suggests a new periodization of 10th century Arabic philosophy. Rather than imagining a Kindian phase followed by a ‘‘school of Baghdad’’ extending from al-Fārābī’s masters to the age of Avicenna, we should postulate that some of al-Fārābī’s followers returned to al-Kindī in the field of cosmology, for theological reasons.

The concept of aerial perspective has been used for the first time by Leonardo da Vinci (1452–1519). This article studies its dependence on Ptolemy's Optica and overall on the optical tradition inaugurated by Ibn al-Haytham's Kitāb al-Manāẓir (d. after 1040). This treatise, that was accessible through several Latin and Italian manuscripts, and was the source of many Medieval commentaries, offers a general theory of visual perception emancipated from the case of the moon illusion, in which physical and psychological factors are closely combined. Atmospheric extinction (not refraction, which is sometimes confused with) affects the conjectured size of remote objects. This phenomenon is also the core source for a pictorial rendering of depth, that is based onto a principle different from the diminution of size.

Textual evidence preserved in two still unpublished manuscripts strongly suggests that there once existed an alternative version of Miskawayh’s Fawz al-aṣghar, the Minor Book of Triumph. The article discusses possible explanations for why Miskawayh may have composed two recensions of his Fawz and compares structure and content of the alternative version with the edited standard version. The one passage which is contained in the alternative Fawz only is presented in Arabic with an English translation. Part of this additional material is parallel to al-Fārābī’s Iḥṣā’ al-‘ulūm, namely its division of natural sciences, and may ultimately derive from a no longer extant treatise by Paul the Persian. An appendix provides the Arabic text and English translation of a hitherto unknown fragment of al-Balkhī in which he discusses Plato’s saying that the world has a causative, but no temporal beginning.

This paper examines the history of glass colouring. It reviews Kitāb al-Durra al-maknūna of Jābir ibn Ḥayyān, which deals with the subject. The manuscript of this practical treatise was discovered recently. Part one of the paper deals with Jābir as a philosopher and chemist. The art of lustre-painting on glass originated in Syria during the Umayyad Caliphate in the eighth century and was soon practised in the neighbouring area. The paper reviews Arabic literature that deals with the colouring of glass until the 13th century, and with pre-Islamic and Latin books of recipes that deal with glass colouring. Recipes for cast coloured glass are very few and scant in non-Arabic literature, and lustre-painting on glass was not mentioned in any treatise outside Arabic, even in the works of Theophilus and Neri. The colouring of glass gemstones by colour diffusion is not mentioned also. The paper compares the recipes of Kitāb al-Durra with the results of modern analysis of existing Islamic stained glass objects. There is a close correspondence, and the main indispensable ingredients in both cases are silver and copper compounds. Part one ends with an account of lāzaward as cobalt oxide in glass colouring. Part two of the paper gives a representative selection of recipes from Kitāb al-Durra for the three methods of glass colouring.