In a letter to his friend Abui Ja‘far Yusuf ibn Hasday, studied by J. al-‘AlawI, Avempace describes his scientific career. He first studied mathematics, music, and astronomy. He then became interested in logic, and later, again in the physical sciences. In the last period of his life, not yet begun at the time of writing the letter, he wrote a series of works, culminating with The Regimen of the Solitary (Tadbtr al-mutawahitid), which had an enormous impact on posterity. Most of the works from the first period of his life have not survived, but we do know that he wrote a commentary on al-Farabl’s The Major Book of Music. We also know of a short writing on the relations between the humors of the body, the strings of the lute, and the melodies of the spheres. The letter to Ibn Hasday alludes to criticism of the astronomer al-Zarqall (Arzachel, d. 1087) about the calculation of the apogee of Mercury. Other texts allude to research on the Conics of Apollonius of Perga.
Later on, he focused on the study of logic, which was studied in al-Andalus on the basis of the logical works by al-Farabl. Several writings from this period of Ibn Bajja’s lifetime have been preserved: some notes on the Five Chapters (al-Fusul al-khamsa) by al-FarabI (a small propaedeutic treatise), as well as on the Farabian summary of Porphyry’s Isagoge, and on the Farabian commentaries on the Categories, De interpretatione, Prior Analytics, and Posterior Analytics. Although these notes appear more like a collection of glosses than as a full-fledged treatise on logic, elements of systematicity emerge, however, highlighted by a series of successive divisions that define the status of the various branches of logic with respect to other philosophical disciplines. The first of these is the division, within the field of language, between lafz (meaning) and ma‘na (concept, ‘‘intention,’’ pl. ma‘ant), which
Alone is the proper subject of logic. The ma‘anl can in turn be divided into singulars and universals, which allows the setting apart of disciplines such as rhetoric and poetic - which attribute a universal predicate to a singular subject - from philosophy, dialectics, and sophistry, which, notwithstanding the diversity of the nature of their premises, predicate the universal of the universal. The latter is itself either simple or compound, such as the definitions, which consist of genera and differences. The science of definitions is thus an understanding of a compound universal, while the science of simple universals is introduced by the Categories (Maqulat). To reassemble universals (or singulars) into complex predications, and further into syllogisms, gives rise to the various sciences, depending on the status of the syllogisms used therein.
Just as with logic, most of Ibn Bajja’s writings of physics do not rest on a direct study of the works of Aristotle, but rather on Graeco-Arabic abbreviations or commentaries of Alexander of Aphrodisias, Themistius, Philoponus, etc.; he uses paraphrases of the Physics and the Meteorology as well as of the De generatione et corruptione. The writings of Ibn Bajja on the physical sciences did become important sources for the early writings of Averroes and his Compendia of natural philosophy. The commentary on the Physics presents some corrections and moderated critiques of Aristotle’s dynamics. He for example considers it necessary to posit a cause for unnatural motion, in addition to the movement imparted by the originator of the motion: this cause must be an immaterial kinetic force inherent in the moved object. The theory of falling bodies that Ibn Bajja formulates is based on his reading of the Arabic Philoponus, and allows for the explanation of how a motion having a finite speed can take place in an environment offering no resistance, as in the case of the celestial bodies, thus leading the way to a dynamic model applicable to both the sublunary and the celestial world. These developments, endorsed by Averroes in his Great Commentary on the Physics, might have influenced John Buridan, whose model was the starting point of Galileo’s discoveries.
Ibn Bajja’s commentary on the De generatione et corruptione follows roughly the order of the exposition of Aristotle’s text, but some conceptual innovations are noteworthy, for example, the fact that the commentary pivots around the distinction - not explicitly mentioned by Aristotle - between the generation of the four simple bodies (kawn al-basa’it) from each other, and the generation of composite bodies (kawn al-murakkablt). This distinction elicits the foundation of the hierarchy of natural beings (i. e., simple body, homeomer composites, anhomeomer organs, animal, and human) which is the foundation and guiding principle of Ibn Bajja’s physics, linking together the latter and the science of the soul.
Ibn Bajja frequently cites the Arabic version of the Nicomachean Ethics and a commentary on it by Porphyry (in twelve instead of ten books, as in Aristotle’s original work) that is mentioned in the Arabic sources. A small epistle, possibly spurious, also undertakes to defend al-Farabi against the accusation of having, in his own lost commentary on Ethics, denied the possibility of the union of humans with the separated Intellect. Ibn Bajja also composed a commentary on Pseudo-Aristotle’s De plantis. An important role is attributed to the Book of Animals (Kitab al-Hayawan), the Arabic summary of the three main zoological treatises of Aristotle, of which only the De generatione animalium and the De partibus animalium are commented upon in Ibn Bajja’s own Kitab al-Hayawan. Zoology is not a peripheral science of lesser importance, but a higher part of physics, which serves as an introduction to the science of the human soul and intellect. It is particularly Aristotle’s account of De gen. an. II, 3 (736a35-b15), on the successive appearance in humans of the faculties imprinted in the living soul, which for Ibn Bajja provides a model for hierarchically arranging the natural forms realized on lower substrates, that then organize themselves in a continuous way, from the simple elementary forms to the forms of the living beings and eventually to the intellect. Of particular importance in the commentary on De animalibus is the comparison between natural and artifactual forms, by which Ibn Bajja shows how the formative power (vis formativa), which gives form to living beings, cumulates the qualities of the artifactual forms - that depend upon an intelligence extrinsic to the created object - and those ofthe substantial and intrinsic natural form. The design of the hierarchy of forms implemented in Ibn Bajja’s Kitab al-Hayawan also serves as a guide to his Book on the Soul (unfinished), which, beginning from the cognition of the forms of simple bodies, studies their composition in complex bodies and the successive combinations that lead to the existence of living beings with a soul. He borrows this from the De anima by Alexander of Aphrodisias, rather than from the work of Aristotle, to which Ibn Bajja does not refer directly.
World History
