Many studies on the astrolabe were written during the period from the ninth to the eleventh century, but very few of them related to projection, i.e., to the geometrical transformation underlying the design of the instrument. Among those that did, the treatise entitled The Art of the Astrolabe, written in the tenth century by Abū Sahl al-Qūhī, represents a particulary important phase in the history of geometry. This work recently appeared in a critical edition with translation and commentary by Roshdi Rashed. It contains the earliest known theory of the projection of the sphere, a theory developed in a commentary written by a contemporary mathematician, Ibn Sahl. Following R. Rashed, the present article offers here a thorough mathematical analysis of al-Qūhī's treatise and of the commentary by Ibn Sahl. It also presents, with commentary, an account of a contemporary treatise on the projection of the sphere, written by al-[Sdotu]āġānī. The latter work is concerned with the conical projection of a sphere on a plane, from a point on an axis of the sphere, other than its pole. The author consciously avoids the case of stereographic projection, but he studies all the other cases of conical projection which, if we employ the terms of al-Qūhī's theory, are compatible with the movement of the instrument (i.e. the rotation of the sphere around its axis). These three texts provide clear evidence of the emergence, during the second half of the tenth century, of a new field of study, that of projective geometry.

The purpose of the article is to present further information about Avicenna's work on Eastern philosophy, supplementing what was written in the author's Avicenna and the Aristotelian Tradition (Leiden, 1988), pp. 115-30. In view of the prevalent but unfounded notions among some students of Avicenna that the Eastern philosophy is mystical or illuminationist, an initial section traces the history of the development of these tendentious ideas first to Ibn T[dotu]ufayl and then to the followers of his interpretation in the West in the nineteenth and twentieth centuries. Further sections discuss the title of the book, list its contents insofar as they can be reconstructed from Avicenna's statements and the extant portions, and provide additional information about its manuscripts and transmission. The style of the work is then analyzed and compared with that of the šifā' in order to verify Avicenna's claim in the Preface to the latter work that the difference between the two was merely stylistic. A final section gives a table of concordance between the contents of the extant part on physics and the corresponding sections in the šifā', establishing the direct relationship and verbal congruity between the two works.

Did classical kalām debates about how thing (šay') and existent (maw[gcaron]ūd) relate to each other pave the way for Avicenna's distinction between essence (māhiyya) and existence (wu[gcaron]ūd)? There are some indications that the concept of thingness (šay'iyya) may have played a bridging role between the mutakallimūn's discussions and those of Avicenna. Nevertheless, Avicenna's appeals to thingness occur most densely in passages devoted to analyzing the relationship between efficient and final causes, an entirely Aristotelian topic. A philological question arises: should these passages be emended to read causality (sababiyya) in place of thingness (šay'iyya)? I argue that the balance of evidence compels us to retain thingness. For Avicenna, thingness is the respect in which the final cause is prior to the efficient cause (as well as to the formal and material causes); existence, by contrast, is the respect in which the efficient cause is prior to the final cause. In fact, over the course of Avicenna's career a progression from the kalām problematic of šay' v. maw[gcaron]ūd to his own problematic of māhiyya v. wu[gcaron]ūd can be detected in his discussions of efficient and final causation.

This article continues and improves the research already accomplished in Géométrie et dioptrique au Xesiècle (1993). It presents two fragments and an additional treatise which enlarge our understanding of the work of Ibn Sahl on the geometrical constructions and projections. All the necessary corrections are included.

Our aim here is to show that an enigmatic text of Avicenna's Glosses, devoted to the problem of evil, takes on its full meaning in the light of the last chapter of the šifā' on De generatione et corruptione. We will see how Avicenna, deepening and developing a cosmological argument already present in the commentary of Alexander of Aphrodisias on the De generatione, ends up building most of his theodicy on the relative incommensurability of the different celestial periods. All the problem of divine Justice is thus reinterpreted in terms of opposition between discrete and continuous. Finally we will show the importance that this development of Avicenna had in Western Christendom in the 14th century, and the complex relationship which Leibniz has with it in his recently edited reflections on the Great Year.

The question of which areas of the earth are fit for human habitation and which ones are not is dealt with in several Hebrew scientific texts of the twelfth and thirteenth century. Medieval Jewish scholars such as Abraham bar [Hdotu]iyya, Samuel ibn Tibbon, and the three thirteenth-century Hebrew encyclopedists were familiar with theories of the oikoumene and its boundaries through Arabic sources. These Hebrew texts display a variety of views on the earth's habitability, all of which ultimately go back to antiquity. Whereas some texts adopted a division of the inhabited portion of the earth into seven climes, others divided the earth into five zones of temperature, of which two were habitable and three were not owing to extreme temperatures. Some of these Jewish authors also pay attention to the question of how climatological or astrological conditions in a given region influence the mental constitution of its inhabitants.

As for Avicenna the human soul is a complete substance which does not inhere in the body nor is imprinted in it, asserting its survival after the death of the body seems easy. Yet, he needs the body to explain its individuation. The paper analyzes Avicenna's arguments in the De anima sections, V, 3 & 4, of the Shifā' in order to explore the exact causal relation there is between the human soul and its body and confronts these arguments with relevant passages in the Metaphysics. It argues that the causal relation between body and soul remains obscure and that, though Avicenna claims that there is a personal immortality and that the disembodied soul remains individuated, he does not provide a satisfactory ontological account for it.

The Hippocratic Aphorisms is a well-known treatise which was very popular throughout the ages. This paper studies the Arabic translation of [Hdotu]unayn ibn Ishaq, the renowned Arab translator, of the first book of the Aphorisms as well as the commentary of Ibn al-Nafīs, the thirteenth-century Arab doctor, on the same book. This study highlights the difficulties that occasionally confronted the Arab commentator while commenting. The obscurity of a few Hippocratic sentences as well as [Hdotu]unayn's interpretation and alteration in meaning were probable sources for those difficulties. Ibn al-Nafīs, however, was unaware of the role played by [Hdotu]unayn in shaping the Arabic text. Ibn al-Nafīs reflected a deep trust in the Arabic text to the degree of commenting on every single word. He used both his intellect and his knowledge of other commentaries to solve those problematic phrases. He did not exhibit an interest in philological matters to help explain the text. His commentaries reflect his respect and appreciation for both Hippocrates and Galen, the latter of whom exercised some influence on [Hdotu]unayn and Ibn al-Nafīs in their understanding of the work. Nonetheless both [Hdotu]unayn and Ibn al-Nafīs showed traces of independence from Galen's influence.

Al-šahrastānī, who confronts Avicenna in several of his works, devoted an entire work to criticizing him, the title of which was The Struggle against the Philosophers. Although unfinished, it nevertheless includes five “questions” out of the seven which its author had foreseen. These concern themes fundamental for philosophy and theology: being, God, the world and its creation. The method according to which al-šahrastānī deals with them is both radical - he is well aware of the central and sensitive points of Avicenna's philosophy, in particular the status of the first emanated Intelligence - and analytical, as it submits Avicenna's technical terms to a rigorous semantic examination, and takes apart those which have the form of syntagmas (such as “The Being necessary by itself”). The foundation of this merciless refutation is adherence to prophecy, as opposed to the attitude of the philosophers.