(b. Sussex, England, ca. 1230–1235; d. Mortlake, Surrey, England, 8 December 1292)
optics, cosmology, mathematics.
Pecham was probably born in the vicinity of Lewes in Sussex, possibly in or near the village of Patcham, and received his elementary education at the priory of Lewes.1 He later matriculated in the arts faculties at Paris and Oxford, probably in that order. He became a Franciscan in the late 1240’s or in the 1250’s and was sent to Paris to undertake theological studies between 1257 and 1259.2 In 1269 he received the doctorate in theology and for the next two years served as regent master in theology. Pecham returned to Oxford in 1271 or 1272 as eleventh lecturer in theology to the Franciscan school, a position he held until his appointment as provincial minister of the order in 1275. Two years later he was called to Italy as master in theology to the papal curia, and in 1279 he was elected archbishop of Canterbury. During his thirteen years as archbishop, Pecham maintained a zealous program of reform. He conscientiously endeavored to improve the administration of his province and persistently fought the practices of plurality and nonresidence; he called two reform councils and opposed, at every opportunity, the spread of “dangerous” philosophical novelties.
Of Pecham’s intellectual development we know very little, although the major forces shaping his outlook probably came from within his own order. In the thirteenth century the Franciscan Order was a stronghold of Augustinianism and, consequently, of opposition to the new Aristotelian and Averroist ideas penetrating Europe. It is thus no surprise that Pecham became one of the leaders in the resistance against heterodox Aristotelian, and even more moderate Thomist, innovations.3 But the Franciscan Order could provide more than antagonism toward philosophical and theological novelties. Among the English Franciscans a tradition of mathematical science had been initiated by Robert Grosseteste (who lectured to the Franciscans at Oxford an probably bequeathed his library to them at his death) and advanced by Roger Bacon. There can be little doubt that this tradition influenced Pecham: there is ample evidence that he and Bacon were personally acquainted and, indeed, resided together in the Franciscan friary at Paris during the period when Bacon was writing his principal scientific works. Nevertheless, this should not be taken to mean that Pecham was Bacon’s student or protégé (there is no evidence for either) or that the influences on Pecham were limited to the Franciscan Order; Pecham’s optical works, for example, reveal the influence not only of Augustine, Grosseteste, and Bacon but also of Aristotle, Euclid, al-Kindi, Ibn al-Haytham, Moses Maimonides, and perhaps Ptolemy and Witelo; and the primary influence in this instance was not Augustine or Grosseteste or Bacon, but Ibn al-Haytham.
Works. Pecham’s indisputably genuine works on natural philosophy and mathematical science are Tractatus de numeris (or Arithmetica mystica); Tractatus de perspectiva; Perspectiva communis, extant in both an original and a revised version; and Tractatus de sphera. In addition to these, a treatise entitled Theorica planetarum is attributed to Pecham in several manuscripts and has commonly been regarded as genuine, although the question of its authenticity has in fact never been explored with care. Material of considerable scientific import is alos contained in Pecham’s treatises on the soul, Tractatus de anima and Questiones de anima, and his Questiones de beatitudine corporis et anime.4 Two other scientific treatises have also been attributed to Pecham, Perspectiva particularis and Tractatus de animalibus, but there is no evidence supporting either attribution.
Of Pecham’s scientific works only those on optics have been subjected to serious scrutiny; nevertheless, it is possible to make a few remarks about several of the others. The Tractatus de sphera was apparently a rival to, rather than a commentary on, Sacrobosco’s De sphaer5 In this work Pecham presents an elementary discussion of the sphericity (or circularity) of the principal bodies of the world (for instance, the heavens, raindrops, and solar radiation passing through noncircular apertures); the rotation of the heavens; the equality and inequality of days; the climatic zones of the terrestrial sphere; the origin of eclipses; and other topics of a cosmologic nature.
The Tractatus de numeris begins with the classification of number into abstract and concrete; concrete number is further subdivided into corporeal and spiritual number, spiritual number is divided into five additional categories, and so on. After further discussion of the elementary properties of numbers (odd and even, equality and inequality) and the perceptibility of number by the external senses, Pecham turns to the mystical properties of numbers: he employs number to elucidate the mysteries of the Trinity and concludes with an analysis of the mystical meanings of the numbers 1 to 30, 36, 40, 50, 100, 200, 300, and 1,000.
The earliest of Pecham’s optical works was the Tractatus de perspectiva, probably written for the Franciscan schools during Pecham’s years as a teacher at Paris or Oxford (1269–1275) or possibly during his provincial ministership (1275–1277). It is a rambling piece of continuous prose, not divided into propositions like the later Perspectiva communis, that treats the full range of elementary optical matters. Like the Tractatus de numeris, and unlike the Perspectiva communis, it is filled with quotations from the Bible and patristic sources, especially Augustine, that give it a theological and devotional flvor. With a few exceptions the Tractatus de perspectiva and Perspectiva communis are identical in theoretical content, although each includes certain topics that the other omits.
The work on which Pecham’s fame has chiefly rested is the Perspectiva communis, probably written between 1277 and 1279 during Pecham’s professorship at the papal curia6 In the first book Pecham discussed the propagation of light and color, the anatomy and, physiology of the eye, the act of visual perception, physical requirements for vision, the psychology of vision, and the errors of direct vision. In book II he discussed vision by reflected rays and presented a careful and sophisticated analysis of image formation by reflection. Book III was devoted to the phenomena of refraction, the rainbow, and the Milky Way.
The central feature of Pecham’s optical system and the dominant theme of book I of the Perspectiva communis is the theory of direct vision. Here, as elsewhere, Pecham endeavored to reconcile all the available authorities-Aristotle, Euclid, Augustine, al-Kindi, Ibn al-Haytham, Ibn Rushd, Grosseteste, and Bacon. Following Ibn al-Haytham, Pecham argued that the emission of visual rays from the observer’s eye is neither necessary nor sufficient as an explanation of sight; the primary agent of sight is therefore the ray coming to the eye from a point on the visible object. But in an attempt to follow Aristotle, al-Kindi, and Grosseteste as well, Pecham argued that visual rays do nevertheless exist and perform the important, but not always necessary, function of moderating the luminous rays from the visible object and making them, “commensurate with the visual power.” Thus Pecham, like Bacon, resolved the age-old debate between the emission and intromission theories of vision in favor of a twofold radiation, although, to be sure, priority was given to rays issuing from the visible object.
The rays issuing from points on the visible object fall perpendicularly onto the cornea and penetrate without refraction to the sensitive ocular organ, the glacial humor (or crystalline lens); nonperpendicular rays are weakened by refraction and therefore can be largely ignored. Since only one perpendicular ray issues from each point of the visible object and the collection of such perpendicular rays maintains a fixed order between the object and the eye, a one-to-one correspondence is established between points on the object and points on the glacial humor, and unconfused perception of the visual field is thus achieved. Vision is not “completed,” however, in the glacial humor. There is a further propagation of the rays (or species) through the vitreous humor and optic nerve to the common nerve, where species from the two eyes combine, and eventually to the anterior part of the brain and the “place of interior judgment.”
Pecham’s optical system included significantly more than a theory of direct vision. He briefly discussed the doctrine of species; treated at length the propagation of rays; and developed a theory to explain how solar radiation, when passing through noncircular apertures, gives rise to circular images. He expressed the full law of reflection and applied it to image formation by plane, spherical, cylindrical, and conical mirrors; in this analysis he revealed an implicit understanding of the nature of the focal point of a concave mirror. Although he did not possess a mathematical law of refraction, he successfully applied the general qualitative principles of refraction to the images that result from refraction at plane and circular interfaces between transparent media of various densities. In his discussion of the rainbow Pecham again attempted to reconcile different theories. He argued that all three kinds of rays (rectilinear, reflected, and refracted) concur in the generation of the rainbow.
Significance and Influence Pecham saw himself primarily not as a creative scientific thinker but as an expositor of scientific matters in elementary terms. He remarked at the beginning of the Tractatus de sphera.
In the present opusculum, I intend to explain the number, figure, and motion of the principal bodies of the world (as well as related matters) insofar as is sufficient for an understanding of the words of Holy Scripture. And certain of these matters I have found treated in other works, but because of their difficulty, brevity, and in some cases falsity, they are useless for the elementary students that I intend to serve.7.
In the Tractatus de perspectiva he remarked that he had undertaken to discuss light and number “for the sake of my simpler brothers,” and in the preface to the Perspectiva communis he indicated that his goal was to “compress into concise summaries the teachings of perspective, which [in existing treatises] are presented with great obscurity.”8 Pecham’s significance in the history of science is principally the result of his success in achieving this goal. He is most notable not as one who formulated new theories and interpretations, although on many occasions he did, but as one who skillfully presented scientific knowledge to his contemporaries and posterity by writing elementary textbooks.
Pecham’s success was greatest in the case of the Perspectiva communis. This text is still extant in more than sixty manuscripts and went through twelve printed editions, including a translation into Italian, between 1482 and 1665. It was used and cited by many medieval and Renaissance natural philosophers, including Dominicus de Clavasio, Henry of Langenstein, Blasius of Parma, Lorenzo Ghiberti, Leonardo da Vinci, Albert Brudzewski, Francesco Maurolico, Giambattista della Porta, Girolamo Fabrici, JOhannes Kepler, Willebroad Snellius, and G. B. Riccioli. It was lectured upon, in the late Middle Ages, at the universities of Vienna, Prague, Paris, Leipzig, Cracow, Würzburg, Alcala, and Salamanca9 The Perspectiva communis was the most widely used of all optical texts from the early fourteenth until the close of the sixteenth century, and it remains today the best index of what was known to the scientific community in general on the subject.
1. The evidence for both claims is a letter written by Pecham in 1285, in which he refers to his “nourishment from childhood” in the vicinity of the priory of Lewes and the comforts and honors he has received from its teachers; see Registrum epistolarum, III, 902 Several historians have argued that Pecham was born in Kent rather than Sussex.
2. In assigning the latter dates, I am following Douie, Archbishop Pecham, p. 8.
3. On Pecham’s position vis-à-vis Averroism and Thomism, see Fernand van Steenberghen, The Philosophical Movement in the Thirteenth Century (Edinburgh, 1955), 94–104. Van Steenberghen calls Pecham “the true founder of neo-Augustianism” (p.103).
4. Scientific content is especially evident in the Questiones de beatitudine corporis et anime, in Johannis Pechami Quaestiones tractantes de anima, Hieronymus Spettman, ed., which is Beiträge zur Geschichte der Philosophie des Mittelalters,XIX, pts. 5–6 (Münster, 1918), although Pecham’s psychology is apparent in all of them. On Pecham’s psychology see Sharp, Franciscan Philosophy, 185–203; and Die Psychologie des Johannes Pecham Spettman, ed., which is Beiträge zur Geschichte der Philosophie des Mittelalters, XX, pt. 6 (Münster, 1919).
5. According to Thorndike, Sphere of Sacrobosco, 24–25.
6. The dating of the Perspectiva communis is discussed in Lindberg, Pecham and the Science of Optics, 14–18; and in Lindberg, “Lines of Influence in Thirteenth-Century Optics: Bacon, Witelo, and Pecham,” in Speculum, 46 (1971), 77–83.
7. Latin text in Thorndike, op. cit., 445.
8. See Lindberg’s eds. of these two treatises for the texts.
9. For a fuller account of the influence of the Perspectiva communis, see Lindberg, Pecham and the Science of Optics 29–32
I. Original Works. The Perspectiva communis (in both the original and the revised versions) is available in a recent ed. and English trans. by David C. Lindberg, John Pecham and the Science of Optics (Madison, Wis., 1970). The known extant MSS and eleven early printed eds. are listed in the to this ed . Pecham’s other optical work, the Tractatus de perspectiva, is also available in a modern critical version, David C. Lindberg, ed., in Franciscan Institute Publications, Text Ser. no. 16 (St. Bonaventure, N.Y., 1972).
No other complete scientific work of Pecham has been printed. The first five chapters of the Tractatus de numeris have been edited from four MSS and published as an appendix to Traetatus de anima Ioannis Pecham, Gaudentius Melani, ed. (Florence, 1948), 138–144. Lynn Thorndike has published the opening paragraphs and incipits of later paragraphs of the Tractatus de sphera in The Sphere of Sacrobosco and Its Commentators (Chicago, 1949), 445–450; and Pierre Duhem has published the section on pinhole images from this same work in Le système du monde, III (Paris, 1915), 524–529. The Theorica planetarum is extant only in MS.
For a full listing of Pecham’s works, including extant MSS and eds., see Victorinus Doucet, “Notulae bibliographicae de quibusdam operibus Fr. Ioannis Pecham O.F.M.,” in Antonianum, 8 (1933), 207–228, 425–459; Palémon Glorieux, Répertoire des maitres en théologie de Paris au XIIIe siècle, II (Paris, 1933), 87–98; and Fratris Johannis Pecham quondam archiepiscopi Cantuariensis Tractatus tres de paupertate, C. L. Kingsford et al., eds. (Aberdeen, 1910), 1–12.
II. Secondary Literature. The best biography of Pecham is Decima L. Douie, Archbishop Pecham (Oxford, 1952). Other valuable sources on Pecham’s life and thought are David Knowles, “Some Aspects of the Career of Archbishop Pecham,” in English Historical Review, 57 (1942), 1–18, 178–201; Hieronymus Spettman, “Quellenkritisches zur Biographie des Johannes Pecham,” in Franziskanische Studien, 2 (1915), 170–207, 266–285; and D. E. Sharp, Franciscan Philosophy at Oxford in the Thirteenth Century (Oxford, 1930), 175–207. For a short biographical sketch and additional bibliography, see Lindberg, Pecham and the Science of Optics, 3–11.
Pecham’s optical work has been most fully analyzed in the following works by David C. Lindberg: John Pecham and the Science of Optics; “The Perspectiva communis of John Pecham: Its Influence, Sources, and Content,” in Archives internationales d’ historire des sciences, 18 (1965), 37–53; “Alhazen’s Theory of Vision and Its Reception in the West,” in Isis, 58 (1967), 321–341; and “The Theory of Pinhole Images From Antiquity to the Thirteenth Century,” in Archive for History of Exact Sciences, 5 , no. 2 (1968), 154–176. Brief descriptions of Pecham’s other scientific works are found in Registrum epistolarum fratris Johannis Peckham archiepiscopi Cantuariensis, Charles T. Martin, ed., III (London, 1885), lvi-cxlv; and Lynn Thorndike, “A John Peckham Manuscript,” in Archivum Franciscanum Historicum, 45 (1952), 451–461.
David C. Lindberg
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