The study of geometrical optics is rarely connected with theological speculation. Nor is astrology usually linked with elements and essences. Nor do prayer and the physical composition of compound medicines usually appear together as a unit of analysis. The ninth-century Arabic philosopher al-Kindi, however, linked all these and more in a causal explanation of why things happen. Al-Kindi, commenting on and extending the (neo-)Platonic and in particular Euclidean theories of vision through rectilinear ray propagation developed an entire philosophical system in which all bodies -- the stars, the planets, and the sun, as well as you, me, apples, clods of dirt, and even qualities -- emit 'rays' which follow optical rules and which interact to determine effects. Each object or substance has its own particular kind of ray, of course, and they can only influence things in certain ways, but this multiplicity approach allowed al-Kindi to construct a philosophical system along astrological lines, but without the absolutism which the Ptolemaic Tetrabiblos provided. It also allowed incorporation of theological ideas of prayer, for so too did the praying devout emit rays that could interact with the plethora of other rays and which might 'cause' the desired effect. Of particular interest to historians of science will be al-Kindi's take on the physicality of the 'rays'. In general, Travaglia argues, al-Kindi thought of the rays as three-dimensional, physical, 'real' entities, but their physicality was not that of our solids, liquids and gasses.
It is in these subtleties that Magic, Causality, and Intentionality reminds us just how differently different cultures can understand reality. Travaglia chose to investigate the Kindian doctrine of rays as part of his wider study of our understanding of al-Kindi's definition of natural magic, in an attempt to explain "everything that happens in nature" (p.39). But this work was also undertaken because of the numerous Kindian texts which survive, those on optics far and away survive more often in Latin translation, hence the interest of traditionally eurocentric medievalists. It is therefore important to realize that while Travaglia specifically denies that this is a study of the transmission of ideas from the Arabic world to the European Middle Ages, it does say something about the medieval European interest in interpreting reality. Further, though, it suggests some new understandings of why those texts were translated and copied so widely. If nothing else, it should remind us that our way of looking at things can be very different from theirs.
The "First Arabic Philosopher", Abu Yusuf Yacqub ibn Ishaq al-Sabbah al-Kindi produced nearly one hundred works in his lifetime (AD 800-873), and although he is not as well known in the West as the eleventh-century Arab philosopher and mathematician Ibn Sinna (Avicenna), or the twelfth-century physician and commentator Ibn Rushd (Averroes), quite a number of his works were translated into Latin in the Middle Ages and exerted a considerable influence on Western thinkers. In particular, his three works under scrutiny in this book -- De radiis, De aspectibus, and De gradibus -- appeared in Europe by the twelfth century (the latter two translated by the indefatigable Gerard of Cremona). De radiis came to be known in Latin as the "Theory of the magical arts" (Theorica artium magicarum) and proposed to its Latin readers the possibility of multiple causality, not just from the stars and planets, but from other objects, and in particular, people themselves through his "doctrine of rays." De aspectibus, or the "Epistle on the difference of perspectives" (Liber de aspectibus) set forth the geometrical rules by which these rays were emitted, propagated (each with its own virtus), and most importantly, discussed the matter of their composition. Finally, De gradibus, whose full title from the Arabic is the "Epistle on knowledge of the strengths of compound medicines" (in Latin, De medicinarum compositarum gradibus) might seem the odd man(uscript) out in this lineup, but Travaglia convincingly shows that in De gradibus al-Kindi uses his ideas of causality by means of emitted rays along with classical ideas of the arithmetical-geometrical intension and remission of degrees to explain the efficacy of physicians' medicines.
Travaglia's treatment of the rays is interesting from a modern point of view, for, despite reiterating the devout nature of many of al-Kindi's works, his rays seem to be an a-theological (not to say atheistic) natural phenomenon. It is in the interaction of rays from natural bodies (including stars, elements, essences, as well as objects and people themselves), and not in direct causal being of either God or 'astral spirits', that things are caused to happen. In one sense this is a scenario which could dispense with a higher being and be supernatural (in the modern sense) for when a person prays for an event, he or she emits rays and they may well interact in such a way with the myriad of other rays such that the desired event happens. In that sense, a higher being is not needed; al-Kindi, though, always retains a place for God, even if His emanations are but another type of ray. The more secular explanation is interesting in a modern context, and one wonders whether this interpretation could ever have been proposed in an earlier, more devout period of our own history.
The first two chapters of Travaglia's book survey previous understandings of causality in Arabic thought and set forth in some detail the "doctrine of rays" as explained in De radiis. The latter task is no mean feat, and Chapter 2 -- the longest and most subtle of the book -- will repay careful rereading by the attentive student. Here Travaglia tries to explain al-Kindi's concept of causality, reciprocity, efficacy and effectiveness, as well as the connection of these ideas of causation to ideas of divine and human agency (through prayer). This leads him to discuss all too briefly at the end of the chapter what I found to be the most intriguing aspect of al-Kindi's philosophical system: the role of imagination in causing effects. Imagination to al-Kindi was a faculty independent of physical reality and also of what we would today call consciousness, and yet it had the power to advance humans toward the divine. This curious privileging of imagination, regarding which Travaglia brings in al-Kindi's work on sleep and dreaming (which was also translated by Gerard of Cremona and exists in at least fourteen Latin manuscript editions), would be an interesting entre'e into an early medieval understanding of the psyche and of human thought. It is worth reiterating that this book is not about the transmission of Kindian ideas to the West, but it does suggest the possibilities for just such a book.
The third and fourth chapters on De aspectibus and De gradibus, respectively, are more explanatory than the more analytical second chapter on De radiis, mirroring the relative levels of abstraction in the three works. De aspectibus is a fairly straightforward treatise on extended geometrical optics, apparently. Beyond the redefinition of the Euclidean two-dimensional rays as actually being three-dimensional and giving them virtus or a power, al-Kindi (or at least Travaglia) seems most interested in the roles of the rays as transforming the air surrounding objects in such a way as to make the objects (and hence, effects) visible. There is a hint of Aristotelian potentiality/actuality in this discussion, but Travaglia suggests that we should in fact see al-Kindi as having gone beyond that classical idea to one of natural agency (as Roger Bacon did), that is, a glimmer of a natural philosophical (read: scientific) outlook on the world. Shifting gears to De gradibus, then, makes more sense in the sequence of this book if we consider the interaction doctors have with their patients through the medium of their medicines. Al-Kindi considered the interaction of elements and elementata, or qualities within the physical compounds administered to patients, as a problem for understanding the interaction of the rays of those elements, elementata as well as the stars, the desires and imagination of the doctor, and of the patient. His goal is of course to understand those interactions and control the efficacy of the medicines. Ultimately, were humanity to understand those interactions and control them, we would have the deepest possible understanding of nature, and it was this that al-Kindi considered true "magic." Thus, the title of the book: Magic, Causality and Intentionality.
Perhaps one of the most important parts of Travaglia's work, however, is the appendix to this volume. Comprising approximately one third of the total number of pages, it provides a catalogue of Kindi's works based upon the Fihrist, a list of Kindi's works drawn up by his near-contemporary Ibn al-Nadim. Travaglia lists each of these 94 works (92 from the Fihrist), along with (A) the surviving Arabic manuscript versions and printed Arabic editions, (B) Latin manuscripts and editions, (C) translation into Western languages, and (D) general bibliography on the particular works. This in itself is a very important addition to Kindian scholarship, allowing direct access -- particularly for English-speaking researchers -- to the relevant research, much of which appeared in the nineteenth century, often in sources that only the major research libraries are likely to hold. With this list in hand, and half a dozen interlibrary loan forms, the Kindian researcher in any institution should be able to have the corpus of secondary sources on her/his desk in a matter of weeks. More importantly, the list of manuscripts, many of which seem not to have been extensively mined, provide fertile ground for further research on Kindi's thought.
The volume is small, but densely argued. All Arabic text has been transliterated into Roman characters with diacriticals and is well explained for those readers (presumably most) who do not read Arabic. Latin quotations, however, are not translated, although in most cases the adjacent paragraphs provide a sense of what the passage says. Editing of the book was clearly done by someone not quite fully fluent in English, but the occasional errors amuse more than confuse (although perhaps there were errors on which I could blame some of my confusion in the deeply philosophical sections; perhaps not). Ultimately, Traviglia has added to the literature a sound commentary on al-Kindi's works, and suggested some interesting avenues of research.