In the first section I outline the theory of abstraction, discussing first its con- ceptual basis, then its psychological-epistemological basis, and last its causal basis. My purpose throughout is to show how these bases, and thus the theory itself, were not only paramountly Aristotelian, but also eminently sensible. In the second section I draw the perspectivist account of vision within the bounds of the theory of abstraction and show stage by stage how that account unfolds coherently within those bounds. This (...) procedure should make clear that what the perspecti- vists actually offered was less a scientific theory of light or vision than a scientifi- cally justified world view. (shrink)

Written by the 11th-century Spanish Arab, Abh Muhammad ibn MucnOn Twilight and the Rising of Cloudsdh's value of around 52 miles remained standard until the 17th century, when it was revised sharply downward in consideration of atmospheric refraction and barometric studies. The treatise itself survives in a single Hebrew exemplar, 25 Latin exemplars, and an Italian exemplar derived from the Latin. At the heart of this present study is a critical text based on a fullscale comparative transcription of 22 of (...) the Latin manuscripts, ranging in date from the 13th to the 17th century. (shrink)

“Although up to now the [visual] image has been [understood as] a construct of reason,” Kepler observes in the fifth chapter of his Ad Vitellionem Paralipomena, “henceforth the [visible] representations of objects should be considered as paintings [ picturae ] that are actual[ly projected] on paper or some other screen.” While not intended as a historical generalization, this claim nonetheless reflects historical reality. Virtually all visual theorists before Kepler did, in fact, conceive of optical images as subjective, not objective constructs (...) – or, to put it in modern terms, as virtual rather than real entities. By current lights, of course, the distinction between virtual and real images is both obvious and common-place: whereas the latter can be physically projected upon a screen, the former cannot. (shrink)

One problem facing Hockney and Falco is the lack of evidence among optical sources to support their claim that artists used image-projection by the early 1400s. After all, if quattrocento artists knew about image-projection, they must have learned about it from experts in the field, and no one was more expert at the time than Perspectivist opticians. As I argue in this paper, however, Perspectivist reflection-analysis posed certain theoretical and conceptual constraints that would have prevented Perspectivist opticians from recognizing, much (...) less understanding, image-projection. Their silence on this matter is therefore not evidence against the Hockney-Falco thesis. (shrink)

In the fifth book of his De aspectibus, the medieval Latin version of Ibn al-Haythamb al-Manir, Alhacen undertakes to determine precisely where a given ray of light will reflect to a given center of sight from a variety of convex and concave mirrors based on circular sections. As applied specifically to convex and concave spherical mirrors, this problem exercised several seventeenth-century thinkers, Christiaan Huygens foremost among them, and in that context it soon became known as Alhazens solution (or solutions) of (...) this problem is deficient in comparison to that of Huygens and later mathematicians. It is my purpose in this paper to show by reconstruction that in fact, far from deficient in any absolute sense, Alhacen’s approach to this problem was remarkably ingenious and elegant in its conceptual simplicity. (shrink)

From the late thirteenth to the early seventeenth century, the process of visual imaging was understood in the Latin West as an essentially subjective act initiated by the eye and completed by the brain. The crystalline lens took center stage in this act, its role determined by its peculiar physical and sensitive capacities. As a physical body, on the one hand, it was disposed to accept the physical impressions of light and color radiating to it from external objects. As a (...) sensitive body, on the other hand, it was enabled by the visual spirit flowing to it from the brain to feel those impressions visually. Acting as a sentient selector of visual information, the lens transformed the brute physical impressions of light and color into visual impressions. These, in turn, gave rise to perceptual “depictions” that were passed back along the stream of visual spirits to the brain. Known in Scholastic parlance as “intentional species,” these depictions served as virtual representations of their generating objects. As such, they provided the wherewithal not only for perception, but also for conception and cognition. (shrink)

That the medieval Latin version of Ibn al-Haytham's Kitāb al-Manā[zdotu]ir was translated into Italian in the fourteenth century has been known for well over a century. Recent studies have shown that this translation, which is contained in Vat. Lat. 4595, was instrumental in the composition of Lorenzo Ghiberti's Commentario terzo on art. Some eight years ago, the author of the present article tentatively identified the actual manuscript-source of that translation as MS Royal 12.G.7, which is currently held in the British (...) Library. This study establishes beyond reasonable doubt that his tentative identification was correct: MS Royal 12.G.7 is indeed the Latin source for the Italian translation in Vat. Lat. 4595. (shrink)

A. Mark Smith - Seeing and Being Seen in the Later Medieval World: Optics, Theology, and Religious Life - Journal of the History of Philosophy 44:3 Journal of the History of Philosophy 44.3 473-474 Dallas G. Denery, II. Seeing and Being Seen in the Later Medieval World: Optics, Theology, and Religious Life. Cambridge Studies in Medieval Life and Thought , 63. Cambridge-New York: Cambridge University Press, 2005. Pp. x + 202. Cloth, $75.00. Among the metaphors we live by , visual (...) metaphors figure prominently in our common discourse about cognition. We are well aware, of course, that in claiming to "see" meanings or "view" ideas in certain lights, we are speaking figuratively. Yet the analogy between thinking and seeing is more than a linguistic artifact. Until the seventeenth century,.. (shrink)

In lieu of an abstract, here is a brief excerpt of the content:Reviewed by:Seeing and Being Seen in the Later Medieval World: Optics, Theology, and Religious LifeA. Mark SmithDallas G. Denery, II. Seeing and Being Seen in the Later Medieval World: Optics, Theology, and Religious Life. Cambridge Studies in Medieval Life and Thought (Fourth Series), 63. Cambridge-New York: Cambridge University Press, 2005. Pp. x + 202. Cloth, $75.00.Among the metaphors we live by (to borrow from Lakoff and Johnson), visual metaphors (...) figure prominently in our common discourse about cognition. We are well aware, of course, that in claiming to "see" meanings or "view" ideas in certain lights, we are speaking figuratively. Yet the analogy between thinking and seeing is more than a linguistic artifact. Until the seventeenth century, Western thinkers took it seriously, none more seriously perhaps than the thirteenth-century scholastic community. The upshot was an epistemology based on two cardinal assumptions: first, that the physical world manifests itself to us through species passing from external objects into the soul, and second, that visual perception is providentially designed to yield a faithful conceptual picture of physical reality and its ordering structure.This latter assumption found strong support in Perspectivist optics, which took mature form in the 1260s as an amalgam of Alhacenian visual analysis and species-theory. Hence, by the later thirteenth century it was widely believed not only that vision is essentially cognitive but also that cognition is essentially visual. During the first half of the fourteenth century, this idea was subjected to trenchant criticism and thereby rejected out of hand by several thinkers, among whom Nicolaus of Autrecourt is a particular subject of emphasis in this study.It has become something of a truism lately that theories are neither accepted nor rejected on logical grounds alone. This one, Denery claims, is no exception since there were compelling theological grounds for its adoption. Foremost among these was a new emphasis on self-presentation in the thirteenth century. That emphasis manifested itself at two levels. On the one hand, the clerical orders were encouraged to give the right appearance and to suit the appearance to specific settings. This was especially important among the new preaching orders, whose members had to put on so many public faces that they came to adopt what Denery calls "heuristics of adaptation." On the other hand, new modes of confession and penance required deep introspection on the penitent's part, so that he might "see" himself for the complex of sinful motives and actions he is, as well as experience the contrition-yielding horror such a sight arouses. In both cases, the appearances should reveal the underlying reality: the preacher's spiritual commitment reflected in his mien, the penitent's contrition in the recognition of his vitiated nature.But how can we be sure that what we see in these instances is true? This question is particularly vexing in the case of religious introspection, for, as St. Paul reminds us, our moral vision is distorted by the mirror that darkens it. Enter the analogy between physical vision and cognition. Visual illusions, such as those arising from reflection, were of paramount concern to Perspectivist theorists, who devoted considerable effort to rationalizing them according to unmet normative conditions, such as adequate illumination, appropriate distance, or a healthy eye. Reflected vision is subject to transgressions of these conditions, but adding insult to their injury is that, when seen in mirrors, objects invariably appear displaced and often look distorted in size, shape, and orientation. Fortunately, reason enables us to rectify such illusions according to specific rules that govern visual perception in general and reflection in particular.If the analogy between physical and moral vision holds true, then reason ought to be the corrective in both cases. At first blush, this seems to be Peter of Limoges's position in the Tractatus moralis de oculo (c. 1280), but, as Denery insists, Peter's real point is that our inner, moral vision is so clouded we can rarely tell either how or even that it is distorted. The hoped-for normative circumstances and principles enabling us to rectify it are far too vague and protean to yield certainty from introspection. Given the tight conceptual linkage between... (shrink)