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Bacon, Roger

Bacon, Roger

(b. England, ca. 1219; d. ca. 1292).

natural philosophy, optics, calendar reform.

Apart from some brief references in various chronicles, the only materials for Roger Bacon’s biography are his own writings. The date 1214 for his birth was calculated by Charles, followed by Little, from his statements in the Opus tertium (1267) that it was forty years since he had learned the alphabet and that for all but two of these he had been “in studio.”1 Taking this to refer to the years since he entered the university—the usual age was then about thirteen—they concluded that in 1267 Bacon was fifty-three and thus was born in 1214. But Crowley has argued that his statements more probably refer to his earliest education, beginning about the age of seven or eight, which would place his birth about 1219 or 1220. Of his family the only good evidence comes again from Bacon himself. He wrote in the Opus tertium that they had been impoverished as a result of their support of Henry III against the baronial party, and therefore could not respond to his appeal for funds for his work in 1266.2.

After early instruction in Latin classics, among which the works of Seneca and Cicero left a deep impression, Bacon seems to have acquired an interest in natural philosophy and mathematics at Oxford, where lectures were given from the first decade of the thirteenth century on the “new” logic (especially Sophistici Elenchi and Posterior Analytics) and libri naturales of Aristotle as well as on the mathematical quadrivium. He took his M .A. either at Oxford or at Paris, probably about 1240. Probably between 1241 and 1246 he lectured in the Faculty of Arts at Paris on various parts of the Aristotelian corpus, including the Physics and Metaphysics, and the pseudo-Aristotelian De vegetabilibus (or De plantis) and the De causis, coincident with the Aristotelian revival there. In arguing later, in his Compendium studii philosophie, for the necessity of knowledge of languages,3 he was to use an incident in which his Spanish students laughed at him for mistaking a Spanish word for an Arabic word while he was lecturing on De vegetabilibus. He was in Paris at the same time as Albertus Magnus, Alexander of Hales (d. 1245),4 and William of Auvergne (d. 1249).5.

The radical intellectual change following Bacon’s introduction to Robert Grosseteste (ca. 1168–1253) and his friend Adam Marsh on his return to Oxford about 1247 is indicated by a famous passage in the Opus tertium:.

For, during the twenty years in which I have laboured specially in the study of wisdom, after disregarding the common way of thinking [neglecto sensu vulgi], I have put down more than two thousand pounds for secret books and various experiments [experientie], and Ianguages and instruments and tables and other things; as well as for searching out the friendships of the wise, and for instructing assistants in languages, in figures, in numbers, and tables and instruments and many other things.6.

Grosseteste’s influence is evident in Bacon’s particular borrowings, especially in his optical writings, but above all in the devotion of the rest of his life to the promotion of languages and of mathematics, optics (perspectiva), and scientia experimentalis as the essential sciences.

He was in Paris again in 1251, where he says in the Opus maius7 that he saw the leader of the Pastoreaux rebels. This story and some later works place him there for long periods as a Franciscan. He entered the Franciscan order about 1257 and, soon afterward, he also entered a period of distrust and suspicion—probably arising from the decree of the chapter of Narbonne, presided over by Bonaventure as master general in 1260, which prohibited the publication of works outside the order without prior approval. Bonaventure had no time for studies not directly related to theology, and on two important questions, astrology and alchemy, he was diametrically opposed to Bacon. He held that only things dependent solely on the motions of the heavenly bodies, such as eclipses of the sun and moon and sometimes the weather, could be foretold with certainty. Bacon agreed with the accepted view that predictions of human affairs could establish neither certainty nor necessity over the free actions of individuals, but he held that nevertheless astrology could throw light on the future by discovering general tendencies in the influence of the stars, acting through the body, on human dispositions, as well as on nature at large. In alchemy Bonaventure was also skeptical about converting base metals into gold and silver, which Bacon thought possible.

Whatever the particular reasons for Bacon’s troubles within the order, he felt it necessary to make certain proposals to a clerk attached to Cardinal Guy de Foulques; as a result, the cardinal, soon to be elected Pope Clement IV (February 1265), asked him for a copy of his philosophical writings. The request was repeated in the form of a papal mandate of 22 June 1266.8 Bacon eventually replied with his three famous works, Opus maius, Opus minus, and Opus tertium, the last two prefaced with explanatory epistole in which he set out his proposals for the reform of learning and the welfare of the Church. It is reasonable to suppose that after twenty years of preparation he composed these scripture preambule to an unwritten Scriptum principale between the receipt of the papal mandate and the end of 1267. In that year he sent to the pope, by his pupil John, the Opus maius with some supplements, including De speciebus et virtutibus agentium in two versions9 and De scientia perspectiva,10 followed (before the pope died in November 1268) by the Opus minus and Opus tertium as résumés, corrections, and additions to it. The pope left no recorded opinion of Bacon’s proposals.

Perhaps at this time Bacon wrote his Communia naturalium and Communia mathematica, mature expressions of many of his theories. These were followed in 1271 or 1272 by the Compendium studii philosophie, of which only the first part on languages remains and in which he abused all classes of society, and particularly the Franciscan and Dominican orders for their educational practices. Sometime between 1277 and 1279 he was condemned and imprisoned in Paris by his order for an undetermined period and for obscure reasons possibly related to the censure, which included heretical Averroist propositions, by the bishop of Paris, Stephen Tempier, in 1277. The last known date in his troubled life is 1292, when he wrote the Compendium studii theologii.11.

Scientific Thought. The Opus maius and accompanying works sent to the pope by Bacon as a persuasio contain the essence of his conception of natural philosophy and consequential proposals for educational reform. He identified four chief obstacles to the grasping of truth: frail and unsuitable authority, long custom, uninstructed popular opinion, and the concealment of one’s own ignorance in a display of apparent wisdom. There was only one wisdom, given to us by the authority of the Holy Scriptures; but this, as he explained in an interesting history of philosophy, had to be developed by reason, and reason on its part was insecure if not confirmed by experience. There were two kinds of experience, one obtained through interior mystical inspiration and the other through the exterior senses, aided by instruments and made precise by mathematics.12 Natural science would lead through knowledge of the nature and properties of things to knowledge of their Creator, the whole of knowledge forming a unity in the service and under the guidance of theology. The necessary sciences for this program were languages, mathematics, optics, scientia experimentalis, and alchemy, followed by metaphysics and moral philosophy.

Bacon leaves no doubt that he regarded himself as having struck a highly personal attitude to most of the intellectual matters with which he dealt, but his writings are not as unusual as the legends growing about him might suggest. They have, on the whole, the virtues rather than the vices of Scholasticism, which at its best involved the sifting of evidence and the balancing of authority against authority, Bacon was conscious of the dangers of reliance on authority: Rashdall draws attention to the irony of his argument against authority consisting chiefly of a series of citations. Most of the content of his writings was derived from Latin translations of Greek and Arabic authors. He insisted on the need for accurate translations. When it was that he learned Greek himself is not certain, but his Greek grammar may be placed after 1267, since in it he corrected a philological mistake in the Opus tertium. He also wrote a Hebrew grammar to help in the understanding of Scripture.

One of the most interesting and attractive aspects of Bacon is his awareness of the small place of Christendom in a world largely occupied by unbelievers, “and there is no one to show them the truth.”13 He recommended that Christians study and distinguish different beliefs and try to discover common ground in monotheism with Judaism and Islam, and he insisted that the truth must be shown not by force but by argument and example. The resistance of conquered peoples to forcible conversion, such as practiced by the Teutonic knights, was “against violation, not to the arguments of a better sect.”14 Hence the need to understand philosophy not only in itself but “considering how it is useful to the Church of God and is useful and necessary for directing the republic of the faithful, and how far it is effective for the conversion of infidels; and how those who cannot be converted may be kept in check no less by the works of wisdom than the labour of war.”15 Science would strengthen the defenses of Christendom both against the external threat of Islam and the Tartars and against the methods of “fascination” that he believed had been used in the Children’s Crusade and the revolt of the Pastoreaux, and would be used by the Antichrist.

Bacon’s mathematics included, on the one hand, astronomy and astrology (discussed later) and, on the other, a geometrical theory of physical causation related to his optics. His assertions that “in the things of the world, as regards their efficient and generating causes, nothing can be known without the power of geometry” and that “it is necessary to verify the matter of the world by demonstrations set forth in geometrical lines”16 came straight from Grosseteste’s theory of multiplicatio specierum, or propagation of power (of which light and heat were examples), and his account of the “common corporeity” that gave form and dimensions to all material substances. “Every multiplication is either according to lines, or angles, or figures.”17 This theory provided the efficient cause of every occurrence in the universe, in the celestial and terrestrial regions, in matter and the senses, and in animate and inanimate things. In thus trying to reduce different phenomena to the same terms, Grosseteste and Bacon showed a sound physical insight even though their technical performance remained for the most part weak. These conceptions made optics the fundamental physical science, and it is in his treatment of this subject that Bacon appears most effective. Besides Grosseteste his main optical sources were Euclid, Ptolemy, al-Kindi, and Ibn al-Haytham (Alhazen). He followed Grosseteste in emphasizing the use of lenses not only for burning but for magnification, to aid natural vision. He seems to have made an original advance by giving constructions, based on those of Ptolemy for plane surfaces and of Ibn al-Haytham for convex refracting surfaces, providing eight rules (canones) classifying the properties of convex and concave spherical surfaces with the eye in various relationships to the refracting media. He wrote:.

If a man looks at letters and other minute objects through the medium of a crystal or of glass or of some other transparent body placed upon the letters, and this is the smaller part of a sphere whose convexity is towards the eye, and the eye is in the air, he will see the letters much better and they will appear larger to him. For in accordance with the truth of the fifth rule [Fig. 1] about a spherical medium beneath which is the object or on this side of its centre, and whose convexity is towards the eye, everything agrees towards magnification [ad magnitudinem], because the angle is larger under which it is seen, and the image is larger, and the position of the image is nearer, because the object is between the eye and the centre. And therefore this instrument is useful for the aged and for those with weak eyes. For they can see a letter, no matter how small, at sufficient magnitude.18.

According to the fifth rule,19 if the rays leaving the object, AB, and refracted at the convex surface of the lens meet at the eye, E, placed at their focus, a magnified image, MN, will be seen at the intersections of the diameters passing from the center of curvature C, through AB to this surface and the projections of the rays entering the eye. As he did not seem to envisage the use of combinations of lenses, Bacon got no further than Grosseteste in speculating about magnifications such that “from an incredible distance we may read the minutest letters and may number the particles of dust and sand, because of the magnitude of the angle under which we may see them.”20.


But he did make an important contribution to the history of physiological optics in the West by his exposition of Ibn al-Hyatham’s account of the eye as an image-forming device, basing his ocular anatomy on Ḥunayn ibn Isḥaq and Ibn Sīnā. In doing so, he seems to have introduced a new concept of laws of nature (a term found in Lucretius and numerous other authors more widely read, such as St. Basil) by his reference to the “laws of reflection and refraction” as leges communes nature.21 His meaning is clarified by his discussion elsewhere of a lex nature universalis22 requiring the continuity of bodies and thus giving a positive explanation, in place of the negative horror vacui, which he rejected, of such phenomena as water remaining in a clepsydra so long as its upper opening remained closed—an explanation comparable to one found in Adelard of Bath’s Natural Questions. Universal nature constituted from these common laws, including those de multiplicatione specierum, was superimposed on the system of particular natures making up the Aristotelian universe—not yet the seventeenth-century concept but perhaps a step toward it.

“Having laid down the roots of the wisdom of the Latins as regards languages and mathematics and perspective,” Bacon began Part VI of the Opus maius, “I wish now to unfold the roots on the part of scientia experimentalis, because without experience [experientia] nothing can be known sufficiently.”23 This science, “wholly unknown to the general run of students,” had “three great prerogatives with respect to the other sciences,”24 The first was to certify the conclusions of deductive reasoning in existing speculative sciences, including mathematics. As an example he gave an investigation of the shape and colors of the rainbow involving both theoretical reasoning and the collection of instances of related phenomena in order to discover their common cause. The second prerogative was to add to existing sciences new knowledge that they could not discover by deduction. Examples were the discovery of the properties of the magnet, the prolonging of human life by observing what plants produced this effect naturally in animals, and the purification of gold beyond the present achievements of alchemy. The third prerogative was to investigate the secrets of nature outside the bounds of existing sciences, opening up knowledge of the past and future and the possibility of marvelous inventions, such as ever-burning lamps and explosive powders.

It is clear that Bacon’s scientia experimentalis was not exactly what this term might now suggest, but belonged equally to “natural magic” aimed at producing astonishing as well as practically useful effects by harnessing the hidden powers of nature. His approach had been profoundly influenced by the pseudoAristotelian Secretum secretorum, of which he had produced an annotated edition variously dated between 1243 and sometime before 1257, but he also insisted that his new science would expose the frauds of magicians by revealing the natural causes of effects. The “dominus experimentorum” of the Opus tertium,25 who may have been Pierre de Maricourt, the pioneer investigator of magnetism, is praised for understanding all these essential characteristics. In the Opus minus,26 Bacon described possibly original experiments of his own with a lodestone held above and below a floating magnet, and argued that it was not the Nautical (Pole) Star that caused its orientation, or simply the north part of the heavens, but all four parts equally. It was in this work, and in the Opus tertium,27 that he inserted his main discussion of alchemy, including the conversion of base metals into gold and silver. There is a further discussion in the Communia naturalium,28 together with sketches of the sciences of medicine and agriculture. In the Communia mathematica29 and the Epistola de secretis operibus artis et naturae et de nullitate magiae, 30 he described more wonderful machines for flying, lifting weights, and driving carriages, ships, and submarines, and so on, which he believed had been made in antiquity and could be made again.

Despite his occasional references to them, Bacon in his accredited writings deals with neither instruments nor mathematical tables in any but a superficial way. For this reason it is hard to measure his stature by comparison with that of his contemporaries whom we should call astronomers and mathematicians. We are not encouraged to set great store by the stories that while in Paris he constructed astronomical tables and supplied the new masters with geometrical problems that none of their audiences could solve.31 His mathematics and astronomy were in fact almost wholly derivative, and he was not always a good judge of competence, preferring, for instance, al-Biṭrūjī to Ptolemy.

Bacon is often held to have achieved a deep and novel insight in regard to the role of mathematics in science, an insight that to the modern mind is almost platitudinous. In this connection it is easy to forget the large numbers of astronomers of antiquity and the Middle Ages for whom mathematics was an essential part of the science, and the smaller numbers of natural philosophers who had made use of simpler mathematical techniques than those of astronomy. It is more to the point to notice that Bacon argued for the usefulness of mathematics in almost every realm of academic activity. Part IV of the Opus maius is devoted to the usefulness of mathematics (1) in human affairs (this section was published separately as the Specula mathematica); (2) in divine affairs, such as chronology, the fixing of feasts, natural phenomena, arithmetic, and music; (3) in ecclesiastical affairs, such as the certification of faith and the emendation of the calendar; and (4) in affairs of state, under which heading are included geography and astrology, When Bacon sang the praises of mathematics, “the first of the sciences,” “the door and key of the sciences,” “the alphabet of philosophy,” it has to be remembered that he used the word in an unusually wide sense. Bacon seemed to fear that mathematics would be dismissed as one of the blacker arts, as when arithmetic was applied to geomancy. He sought “per vias mathematice verificare omnia que in naturalibus scientias sunt necessaria”; and yet in the last resort, experience was still necessary, and in a sense supreme.32.

So loud and long were Bacon’s praises of mathematics that it is hard to avoid the conclusion that his love of the subject was unrequited. He could compose his De communibus mathematice and mention, in geometry, nothing beyond definitions, axioms, and methods. Apart from mathematically trivial results in such practical contexts as engineering, optics, astronomy, and the like, his works apparently contain not a single proof, not a single theorem; and we must take on trust the story of the difficult problems he devised for the young Paris masters. As for his analytical skills and his views on the citation of authority, rather than try to resolve the geometrical paradox of the doctrine of atomism—that it can make the hypotenuse and side of a square commensurable—he preferred simply to dismiss it as being contrary to Euclid.

The standard discussion of ratios in Euclid, Book V, did not include a numerical treatment of the subject, for which the standard medieval authority was the Arithmetica of Boethius. There the different species of ratio are tediously listed and subdivided, and the absence of a similar logical division of ratio in Euclid was complained of by Bacon in Communia mathematica.33 He was not to carry out the program at which he might seem to have hinted, and not until Bradwardine’s Geometria speculativa did the Schoolmen make any progress toward a numerical description of irrational ratios, except perhaps in some halting attempts to elucidate Proposition III of Archimedes’ De mensura circuli.

As for the relation of logic to mathematics, Bacon inverted, in a sense, the logistic thesis of our own century: without mathematics, for instance, the categories were unintelligible.34 Mathematics alone gave absolute certainty. Bacon was unusual in that he generally named his sources, citing such authors as Theodosius, Euclid, Ptolemy, Boethius, al-Fārābī, and—among modern writers-Jordanus de Nemore (De triangulis and arithmetica) and Adelard. Despite his criticism of Jordanus, by any reckoning a better mathematician than Bacon, he had praise for “the only two perfect mathematicians” (of his time), John of London and Pierre de Maricourt. He also condescended to praise Campanus of Novara and a “Master Nicholas,” teacher of Amauri, son of Simon de Montfort. In the last analysis, almost everything Bacon wrote under the title of mathematics is best regarded as being at a metaphysical level. His view that in mathematics we have perfect demonstration reinforced his theory of natural action. His philosophy of science, however, was inherently empiricist: rational argument may cause us to dismiss a question, but it neither gives us proof nor removes doubt.

It was held in the Opus maius that a more accurate knowledge of the latitudes and longitudes of places was needed for (1) knowledge of mankind and the natural world; (2) facilitation of the spiritual government of the world—missionaries, for example, would be saved from danger and from much wasted labor; (3) knowledge of the whereabouts of the ten tribes and even of the Antichrist. His geography was nevertheless a compilation of works on descriptive geography (in which he gave, as it were, an extended verbal map of the world) by such writers as Ptolemy and al-Farghānī, supplemented by the reports of Franciscan travelers, especially to the East.

In the Opus maius35 he stated the possibility of voyaging from Spain to India. The passage was inserted, without reference to its source, in the Imago mundi36 of Cardinal Pierre d’Ailly (d. 1420). Humboldt argued that this passage, quoted by Columbus in a letter of 1498 to Ferdinand and Isabella, was more important in the discovery of America than the Toscanelli letters. Thorndike suggests that Columbus probably did not read the vital work until his return from the first voyage of 1492.37 It is immaterial, as Thorndike points out, whether Bacon was merely optimistically citing Aristotle, Seneca, Nero, and Pliny on the distance of Spain from India. In fact Bacon argued as cogently from such longitudes and latitudes as were available in the Toledan tables as he did from classical authors.

For the radius of the earth Bacon took a figure of 3,245 miles (al-Farghānī). He stated that the earth’s surface was less than three-quarters water. In both cases he selected good figures from a great many authoritative but bad ones. It is clear, nevertheless, from his repetition of the method of determining the size of the earth—a method he look from alFarghānī—that he had no appreciation whatsoever of the practical difficulties it involved.

Bacon appears to have sent a map to the pope with his Opus maius. Although it is now lost, from the description he gave it appears to have included the better-known towns of the world plotted by their latitudes and longitudes as found in many contemporaneous lists.38 We have no knowledge of the projection adopted, but the description is compatible with the use of a rectangular coordinate system.

Bacon used the words “astronomia” and “astrologia” in a typically ambiguous manner, but there is no doubt that he believed in the reasonableness of what we would call astrology. In the Opus tertium he spoke of astrology as the most important part of mathematics, dividing it into a speculative, or theoretical, part, presumably of the sort included in Sacrobosco’s Sphere, and a practical part, “que dicitur astronomia,”39 concerned with the design of instruments and tables.40 A remark in the Opus maius,41 written in 1267, confirms a similar remark made four years later by Robertus Anglicus,42 to the effect that conscious efforts were being made to drive what amounts to a clock (in Bacon’s example the spherical astrolabe was to be driven) at a constant rate. This seems to confirm approximately the terminus ante quem non previously determined for the mechanical clock.

On many occasions Bacon emphasized at length that the two sorts of “astrology” were essential if man was to learn of the celestial influences on which terrestrial happenings depended. By reference to Ptolemy, Haly, Ibn Sīnā, Abū Ma’shar, Messahala, and others, he showed that the best astrologers had not held that the influence of the stars subjugated the human will, and that the Fathers who objected to astrology on these grounds had never denied that astrology could throw light on future events. It was possible to predict human behavior statistically but not with certainty in individual cases. Astrology might strengthen faith in the stability of the Church and foretell the fall of Islam and the coming of the Antichrist; and all these things “ut auctores docent et experiencia certificat.”43 On occasion he likened astrological influence to the influence of a magnet over iron.

In his main works Bacon did not discuss the technicalities of astronomy or astrology, but in both of the works ascribed to him with the title De diebus creticis44 the standard medical astrology of the time is rehearsed. These works are not merely compilations of older authorities. Although technically they are in no sense new, they have a rational cast and even include the testimony of medical men of the time. The first of these two works is interesting because it incorporates the whole of the De impressione aeris attributed to Grosseteste and printed among his works by Baur. Little.45 suggests that Grosseteste (d. 1253) collaborated with Bacon. Internal evidence suggests a date of composition of about 1249. Some planetary positions quoted for that year are sufficiently inaccurate to suggest that the work was written before 1249 rather than after, and that the author was by no means as skilled as the best astronomers of the time.

The Speculum astronomie, of doubtful authorship (see below), is inconsistent with certain of Bacon’s accredited writings. It is essentially a criticism of Stephen Tempier’s decree of 1277 attacking 219 errors, several involving a belief in astrology. As already seen, Bacon’s prison sentence was probably related to the bishop’s decrees.

Bacon’s astronomical influence was slight in all respects, although through Paul of Middelburg he is said to have influenced Copernicus.46 His writings on the calendar were frequently cited.47 Theologians treated the calendar with a respect it did not deserve, regarding it as a product of astronomy, while astronomers would have treated it with more disdain had they been detached enough to perceive it in a historical context. Here Bacon’s skepticism was useful, and whatever the depth of his astronomical knowledge, he wrote on calendar reform with as much insight as anyone before Regiomontanus—Nicholas of Cusa notwithstanding. In discussing the errors of the Julian calendar, he asserted that the length of the Julian year (365 1/4 days) was in excess of the truth by about one day in 130 years, later changing this to one day in 125 years. The length of the (tropical) year implied was better than Ptolemy’s, and indeed better than that accepted in the Alphonsine tables compiled a few years after the Opus maius. (The correct figure for Bacon’s time was one day in a little over 129 years.) The Alphonsine tables imply that the Julian error is one day in about 134 years. There is no reason whatsoever to suppose, as many have done following Augustus De Morgan, that Bacon’s data were his own. Thābit ibn Qurra made the length of the year shorter than the Julian year by almost exactly one day in 130 years, and according to a curious passage in the Communia naturalium, Thābit was “maximus Christianorum astronomus.” In the Computus, however, Thābit is grouped with al-Bāttanī and others who are said to have argued for one day in 106 years, while Asophus (’Abd al-Raḥmān ibn ’Umar al-Sūfī) appears to have been the most probable source of influence, with his one day in 131 years.48.

As a means of reforming the calendar, Bacon seems finally to have recommended the removal of one day in 125 years (cf. the Gregorian method of ignoring three leap years in four centuries), and in connection with Easter since the nineteen-year cycle is in error the astronomical calculation of the feast; otherwise a lunisolar year like that of the eastern nationals should be adopted. (Grosseteste had previously made this proposal) he tempered this rash suggestion with the pious qualification that if an astronomical calculation of Easter was to be adopted, Hebrew astronomical tables should be used. His proposals may be compared with the much less radical ones of Nicholas of Cusa who in his Reparatio calendarii(pre 1437?) merely suggested a temporary patching up of the calendar eliminating a number of days to after the equinox suitably (Gregorian reform, supervised by Clavius took the same superfluous step) and changing the “golden number” so as to make the ecclesiastical moon correspond for a time with reality . These solutions were inferior to Bacon’s including fewer safe guards against a future state of affairs in which Church usage and the ordinances of the Fathers might differ appreciably. It is worth noting that Stöffler proposed to omit one day in 134 years (an obviously Alphonsine parameter), while Pierre d’Atilly followed again in connection with proposal for calendar reform in England We find that in 1582 John Dee had “instructed and admonished” the Romane bishop who was now contented to follow so near the footsteps of Verity”49 Judging by the speed of English legislation in the matter of calendar reform. it seems that Bacon was a little less that five centuries ahead of most of his countrymen.

Little wrote in 1914 The extant manuscripts of Bacon’s works show that the ’Doctor mirabilis never wanted admirers,’ ’ ’50 and cited as evidence the existence of twenty-seven manuscripts of the Perspectiva51 alone, dating from the thirteenth to the seventeenth centuries Apart from his proposals for the Calendar it was on Bacon’s optics that most scientific value was placed, by his contemporary Witelo as well as by Francesco Maurolico John Dee Leonard Digges Hobbes and the first editors of his works At the same time his accounts of alchemy and natural magic gave him more dubious fame varying from the sixteenth to the nineteenth centuries with current popular prejudices.


1.Opus tertium, Brewer ed., p.65.

2.Ibid, p. 16.

3.Compendium studii philosophic, Brewer ed., pp.,467–468.

4.Opus minus, Brewer ed., p. 325; Opus tertium Brewer ed., p.30 Compendium studii philosophie p. 425.

5.Opus tertium, Brewere ed., pp.74–74.

6.Ibid p. 59.

7.Opus matius (1266–1267)Bridges ed., 1 401.

8. Brewere p.1.

9. Cf. Opus maius, Bridges ed., pt IV dist ii-iv and De multipli catione specierum Baridges ed.,.

10. Cf. Opus maius pt. V.

11. Rashdall pp.3.34.

12.Opus maius, VI 1.

13.Ibid, Bridges ed., III 122.

14.Ibid II 377.

15.Opus tertium Brewere ed., pp.3–4.

16.Opus maius Bridges ed., I 143–143.

17.Ibid p. 112.

18.Ibid V.III.ii4 (Bridges ed., II 157).

19. Figure I is redrawn and relettered from Opus matius V.III II 3., brtish Museums Ms Royal 7.f.viii,13th cent f, 93r.

20.Ibid, Bridges ed., II 165.

21.Opus tertium, Duhem ed., pp.78 90; Opus maius Bridges Rd., II 49.

22. Ibid I 151; De multiplicatione specierum, ibid, II 453; Communia naturlium Steele ed., ed., fase 3.pp.220,224.

23.Opus maius, Bridges II 167.

24.Ibid p.172.

25. Brewere ed., pp. 46–47.

26.Ibid., pp. 383–384.

27. Little ed., 80–89.

28. Steele ed., fase 2, pp. 6–8.

29. Steele ed. fase 16, pp.42–44.

30. Brewer ed., p.533.

31.Opus tertium, Brewere ed., pp, 7,36,38.

32. See eg., Opus maius bridges sed., II 172–172.

33. Steele ed., fase 19 p 80.

34.Opus Malus, bridges ed., i 102; cf., Communia mathematica Steele ed., fase 16.p.16.

35. Bridges ed., I 290 ff.

36.Imago mundi was first published at Louvain in 1480 or 1487.

37.A History of Magic and Experimental Science, II 645.

38. Bridges ed., I 300.

39. Cf. Communia mathematica, Steele ed., fase 16, p,49.

40. Brewere p.106. Since in ch XIi of the same work he seems to have used the word “tables” to refer primarily to almanacs i.e. ephemerides, and to have spoken of instruments only as a means of verifying tables, it is probable that here he meant to refer only to the astrolabe and the equatorium.

41. Bridges ed., II, 202–203.

42. See L. Thorndike, The Sphere of Sacrobosco and It Commentators (Chicago 1949), p.72.

43.Opus maius, 1, 385.

44. Steele ed., fase. 9. appendices ii and iii, ed. Little.

45. Little, ibid, p xxx.

46. Bridges ed., I xxxiii 292.

47. See bibliography. Note that the same passage occurs, word for word, in Opus tertium, Brewere ed., pp 271–292; and in Opus maius, Bridges ed., 1, 281 Notice, however, that the computus, written 1263–1265, does not contain and passage from either of these works, and that it acknowledges Arabic, rather than paying lip service to Hebrew, sources.

48. Steele ed., fasc. 6, pp. 12–18.

49. Corpus Christi College, Oxford, MS C. 254, f. 16lr.

50. Pp. 30–30.

51.Opus maius, pt. V.


I. Original Works. A number of baconian problems must remain unsolved until there is a complete critical edition of his works: see the bibliography by Little is Roger Bacon: Essays (Oxford, 1914), pp. 375–426; compare G. Sarton, Introduction to the History of Science, II (Baltimoare, 1931), 963–967; and L. Thorndike and P. Kibre, A Catalogue of Incipits of Mediaeval Scientific Writings in Latin (2nd ed., Cambridge, Mass., 1963).

The earliest of Bacon’s authentic works to be printed was the Epistola de secretis operibus artis et naturae (De mirabili protestate artis et naturae) (Paris, 1542;Basel, 1593); in the Opera, J. Dee, ed. (Hamburg, 1618); in French (Lyons, 1557; Paris, 1612, 1629); in English (London, 1597,1659); in German (Eisleben, 1608); and other eds. After this appeared the De retardandis senectutis accidentibus et de sensibuis conservandis (Oxford, 1590; in English London, 1683); and Specula mathematica (part of Opus maius IV); in qua De specierum multiplicatione earumdemque in inferioribus virtute agitur and Perspectiva (Opus maius V) both ed. J. Combach (Frankfurt 1614). There were other early eds of the doubtful Speculum alchemiae (Nuremburg 1541; in French 1557; English 1597 German 1608; with later reissues) and the collection De arte chymiae scripta (Frankfurt 1603, 1620).

The 1st ed. of the Opus minus by S. Jebb (London 1733), followed by an improved ed. (Venice 1750), both including only pts. I-VI Pt. VII was included in the new ed. by J.H. Bridges, 2 vols. (Oxford, 1897) with a supp vol. (III) of revisions and additional notes (London, 1900). This ed. was trans. into English by R.B. Burke (Philadelphia, 1928). Pt. VII of the actual MS sent to the pope has been ed. by E. Massa, Rogeri Baconi Moralis philosophia (Zurich, 1953). The eds. of Jebb and Bridges (Vols. II and III, pp. 183–185) both include De multiplicatione specierum, a separate treatise forming part of a larger work; a further section of this has been ed. with a discussion of its date and associations by F.M. Delorme Le prologue de Roger Bacon à son traité De influentiis agentium in Antionianum18 (1943) 81–90.

The 1st eds of the Opus minus and the Opus tertium. together with the Compendium studii philosophie and a new ed. of the Epistola de secretis operibus, were by J.S. Brewer in Fr. Rogeri Bacon Opera quaedam hactenus inedita (London, 1859). Further sections of the first two works have been ed. by F. A. Gasquet, “An Unpublished Fragment of Roger Bacon” in The English Historical Review, 12 (1897), 494–517, a prefatory letter and other parts of Opus minus P. Duhem Un fragment inédit de l’ Opus tertium de Roger Bacon (Quaracchi 1909), on optics astronomy, and alchemy; and A. G. Little, Part of the Opus tertium of Roger Bacon, British Society of Francican Studies, IV (Aberdeen, 1912). The last two items include Bacon’s De enigmatibus alkimie. For further parts of the Opus minus, including discussions of alchemy, still unpublished, see A. Pelzer, “Une source inconnue de Roger Bacon, Alfred de Saraeshel, commentateur des Météorologiques d’Aristote,” in Archivium franciscanum historicum,12 (1919), 44–67.

Other work have been ed. by E. Nolan and S. A. Hirsch, The Greek Grammar of Roger Bacon, and a Fragment of His Hebrew Grammar (Cambridge, 1902); H. Rashdall, Fratris Rogeri Baconi Compendium studii theologii, British Society of Franciscan Studies III (Aberdeen 1911); S. H. Thomson, “An Unnoticed Treatise of Roger Bacon on Time and Motion in Isis, 27 (1937) 219–224; and in Opera hactenus inedita Rogeri Baconi, R. Steele, ed. (unless otherwise stated), 16 fasc. (Oxford, 1905–1940); (1) Meta physica: De viciis contractis in studio theologie (1905);(2–4) Communia naturalium (1905–1913); (5) Secretum secretorum cum glossis et notulis (1920); (6) Computus (1926); (7) Questiones supra undecimum prime philosophie Aristoelis (Metaphysica, XII) (1926); (8) Questiones supra libros quatour physicorum Aristotelis, F. M. Delorme, ed. (1928); (9) De retardatione accidentium senectutis cum aliis opusculis de rebus medicinalibus, A. G. Little and E. Withington, eds.(1928); (10) Questiones supra libros prime philosophie Aristotelis (Metaphysica I, II, V-X) (1930); (11) Questiones altere supra libros prime philosophie Aristotelis (Metaphysica, I-IV) Questiones supra de plantis (1932); (12) Questiones supra librum de causis (1935); (13) Questiones supra libros octo Physicorum Aristotelis, F.M. Delorme ed. (1935); (14) Liber de sensu et sensato, Summa de sophismatibus et distinctionibus (1937); (15) Summa grammatica Sumule dialectices (1940); and (16) Communia mathematica (1940). The Chronica XXI V generalium ordinis minorum (ca. 1370) Was pub. in Analecta Franciscana 3 (1897).

II Secondary Literature. The best critical study of Bacon’s life is T. Crowley, Roger Bacon; The Problem of the Soul in His Philosophical Commentaries (Louvain-Dublin, 1950). The pioneering study by E. Charles, Roger Bacon: Sa vie, ses ouvrages, ses doctrines d’aprés des texts inédits (Paris, 1861), is now mostly of historical interest. Essential general studies are A. G. Little, ed., Roger Bacon: Essays Contributed by Various Writers (Oxford, 1914), especially contributions by Little (life and works); L. Baur (Grosseeteste’s influnce); Hirsch (philology); E. Wiedemann, S. Vogl, and E. Würschmidt (optics); Duhem (vacuum); M. M. P. Muir (alchemy); E. Withington (medicine); and J. E. Sandys (English literture); Little, Franciscan Letters, Papers and Documents (Manchester, 1943); L. Thorndike, A History of Magic and Experimental Science, II (New York, 1929) 616–691; S. C. Easton, Roger Bacon and His Search for a Universal Science (Oxford, 1952), with bibliography; and F. Alessio, Mito e scienza in Ruggero Bacone (Milan, 1967).

Studies of Particular aspects are E. Schlund, “Petrus Peregrinus von Maricourt; Sein Leben und seine Schriften,” in Archivum Fransiscanum historicum 4 (1911), 445–449, 636–643; L. Baur, “Die philosophischen Werke des Robert Grosseteste” in Beiträge zur Geschichte der Philosophie des Mittelaters, 9 (1912) 52–63 and “Die Philosophie des Robert Grosseteste,” ibid 18 (1917) 92–120; P. Duhem Le systéme du monde (Paris 1916–1958), III 260–277, 411–442; V, 375–411; VIII, 121–168; A. Birkenmajer, “Études sur Witelo, i-iv,” in Bulletin international de’ l’Académie polonaise des sciences et des letters, Classe d’histoire et de philosophie (1920) 354–360; and “Robert Grosseteste and Richard Fournival,” in Mediaevalia et humanistica, 5 (1948) 36–41; R. Carton L’expérience physique chez Roger Bacon, L’expeérience mystique de I’llumination intérieure chez Roger Bacon, La synthése doctrinale de Roger Bacon, nos. 2,3,5, in the series Études de philosophie médévale (Paris, 1924); C. B. Vanderwalle, Roger Bacon dans l’historie de la philologie (Pairs, 1929) G. Meyer “En quel sens peut-on parler de ’méthode scientifique’ de Roger Bacon,” in Bulletin de litteérature eccleésiastique (Toulouse), 53 (1952) 3–25, 77–98; A. C. Crombie, Robert Grosseteste and the Origins of Experimental Science 1100–1700, 3rd imp. (Oxford, 1969) pp. 41, 139—162, 204–207, 213–218, 278–281, with bibliography; and “The Mechanisic Hypothesis and the Scientific Study of Vision,” in Proceedings of the Royal Microscopical Society2 (1967) 20–30, 43–45; M. Schramm, “Aristotelianism: Basis and Obstacle to Scientific Progress in the Middle Ages,” in History of science, 2 (1963), 104–108; and A. Pacchi, “Ruggero Bacone e Roberto Grossatesta in un inedito hobbesiano del 1634,” in Rivista critica di storia della filosofia, 20 (1965), 499–502.

A. C. Crombie

J. D. North.

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Bacon, Roger


(b. England, c. 1214 or 1220; d. Oxford, England, c. 1292), mathematics, astronomy, natural philosophy. For the original article on Bacon see DSB, vol. 1.

Bacon has long been recognized as a key intellectual figure in the Middle Ages, but interpretations of his role have varied. The previous DSB article on Roger Bacon by

A. C. Crombie and John North will remain a classic and should be consulted. It is particularly important for the account of Bacon’s mathematics and astronomy. Since 1970, however, there have been significant new editions and studies of Bacon’s works on grammar, logic, natural philosophy, astrology, experimental science, and moral philosophy. There has been a real advance in the production of good quality Latin texts with accurate matching geometric diagrams. And so, step by step, scholarship is on the way toward a more critical appreciation of all of the achievements of Bacon as a philosopher, scientist, and moral philosopher/theologian. The only major alteration to the chronology of Bacon is the realization that he returned from Paris to Oxford around 1280.

In 1859, William Whewell set the tone for modern accounts of “Roger Bacon and the Sciences” (Whewell, 1859). He viewed Bacon as an advocate of experiment ahead of his time. Robert Adamson in 1876 considered Bacon a philosopher of science. In the 1900s, Lynn Thorndike (1914, 1916) and Pierre Duhem (Bacon, 1909) asserted that the role of observation in Bacon’s science was minimal and added nothing to the science. A. C. Crombie in his Robert Grosseteste and the Origins of Modern Science (1953) argued that the qualitative aspects of modern science originated at Oxford in the early thirteenth century. This interpretation was not universally accepted.

The present entry brings the scholarship up to date and gives an overview of Bacon’s program of research especially in the light of new textual discoveries and new studies. Much of the recent scholarship has emphasized that Bacon must be seen in the context of his own times and the scientific concerns of those times. To avoid anachronism one should interpret Bacon as a medieval scientist and not as an early modern or modern scientist.

The most significant advances in Bacon scholarship since 1970 have been the following: the discovery of the missing section of Opus maius on signs (De signis). The study of this and related logical texts has led to a better understanding of Bacon’s philosophy of language and semiotics. One has also gained a better understanding of his applications of learning to theology, a more precise knowledge of his understanding of mathematics, the first reliable text of his major work on natural philosophy, De multiplicatione specierum (On the multiplication of species), the first reliable text of the Perspectiva, a better understanding of the sources of the scientia experimentalis, a better knowledge of his moral philosophy.

Life and Works. Bacon remarks in the Opus tertium that around 1267 to 1268 he had devoted forty years to study since he had first learned the alphabet and that no other scholar worked some much in the arts and sciences as he had done. Some scholars use this text to argue that Bacon was speaking about his elementary education and was born c. 1220. Others hold that he was born c. 1214.

With the exception of the logical works, the Aristotelian Quaestiones are found in manuscript, Amiens MS Bibl. Mun. 406. They include two sets of questions on the Physica and the questions on the Metaphysica of Aristotle, the questions on the Liber de causis, the pseudo-Aristotelian De vegetabilibus. A second version of the questions on the Physica has recently been found in Philadelphia MS Free Library, Lewis Europe, ff. 77ra-85rb. It led to new critical research.

The early logical works consist of the Summa gram-matica, Summa de sophismatibus et distinctionibus and the Summulae dialectics (=Summulae super totam logicam). These works show that Bacon was indebted to the teaching of logic at Oxford and Paris in the 1230s and 1240s, especially to Robert Kilwardby. They received much critical study in recent years and show that Bacon was a mature philosopher of logic who was representative of terminist and premodist grammar.

Scholars have long held that Bacon was a pioneer in introducing the study of Aristotle as interpreted by Aver-roës and Avicenna to the University of Paris c. 1240. Recent research has shown that two Erfurt manuscripts

(Stadtbibliothek Q. 290 and Q. 312) once ascribed to Walter Burley (fourteenth century) belong to the first half of the thirteenth century. The editor of the questions on the Physica attributed these to Richard Rufus of Cornwall, a contemporary and opponent of Bacon. This research alters the accepted view of Bacon as the first to teach Aristotle at Paris (see Richard Rufus of Cornwall, 2003).

It has been demonstrated that already in the 1240s, Bacon confronted and reviewed some of the major issues concerning Latin Averroism that would become a vital part of philosophical discussion at Paris in the 1260s and 1270s. One can conclude that by 1248 Bacon ceased being a master of arts at Paris, became an independent scholar, and returned to England. He was back in Paris in 1251.

When Bacon joined the Franciscan order about 1256, he expected that it would support his scholarly work. Instead, he entered a ten-year period of enforced absence from teaching. He had been attracted to the order by the philosophical, theological and scientific example of Robert Grosseteste and Adam Marsh. He had personally known Adam Marsh and may have seen Robert Grosseteste.

Roger Bacon and Science. The Opus minus, minus, tertium, the related foundational work in philosophy of nature, De multiplictione specierum, and the work on burning mirrors, De speculum comburentibus, together with an optical lens, were sent to the pope c. 1267 to 1268. They were seen as a preamble to a major work on philosophy. Together with these in the 1260s, he produced the Communia naturalium, Communia mathematica, Epistola de secretis operibus naturae et the nullitate magiae. The Compendium studii philosophiae can be dated to about 1271. This is largely a work of polemic on the state of studies in Paris. The edition of the important work in medieval politics and statecraft in Latin translation from the Arabic, the Secretum secretorum, was completed at Oxford about 1280. The Compendium studii theologiae is usually dated to c. 1292.

One must bear in mind that Bacon in the 1260s is writing as an individual author for a patron, Pope Clement IV. Although a onetime master of arts, he was no longer a teaching master at the university. Still, much of his polemic is centered on the struggles in the arts and theology at Paris. The pope instructed Bacon in 1266 to ignore the rules of his order and to send him his remedies about a matter of some importance. What does this mean?

Bacon offered a structural critique of the scholastic practice in the universities. He favored language study and science over Sentence Method, and advocated training in mathematics and the sciences as requirements for students in theology. Bacon’s later works on languages and sciences were written in the specific historical and political context of the Mongol invasion of Europe, the sack of Baghdad in 1258, and the geopolitical situation of a Europe hemmed in by both the Mongols and Islam. His sense of world geography was aided by the travel reports of William of Roebruck. Bacon offered a criticism of the Latin Averroism/radical Aristotelianism of the schools.

The overall division of the Opus maius is Stoic: language study, natural philosophy/mathematics, and morals. The general context is theological: the arts and sciences leading to human well-being in this world and the next. Part One examines the causes of error in education and is critical of some theological limits on science. These causes are: belief in unworthy authority, long custom, uncritical popular opinion, and concealment of academic ignorance in a display of rhetorical wisdom. Part Two contains the pre-Cartesian view of truth and wisdom as a result of a universal revelation to the Hebrews that was transmitted through the Greeks, Romans, and Islam to medieval Christianity. Part Three deals with language study, grammar, semantics, and semiotics. Bacon’s semiotics is now seen as very important for medieval logic. His account of semiotics, De Signis, was discovered in 1978 (Fredborg, Nielsen, Pinborg, 1978). Bacon’s proposals were radical. He advocated language training in Hebrew and Greek. He wrote Hebrew and Greek grammars. Bacon’s ontology pointed toward the priority of the individual and the realist/nominalist issues in medieval thought.

Parts Four, Five, and Six of the Opus maius present the main themes of Bacon’s contribution to scientific education. In addition, one should add the scientific works mentioned above. It is important to see Bacon’s main contribution to science as one who advocated scientific education in an arts faculty that was dedicated to the linguistic arts. Bacon had a very wide reading knowledge of most of the newly translated work from Greek, Jewish, and Islamic philosophy and science. His major claim to fame in science is that he was the first Latin thinker to comprehend and write on most of the ancient sources of Optics. In brief, he initiated the tradition of Optics/Perspectiva in the Latin world. This tradition would be formulated as teaching text by both John Pecham and Witelo of Silesia, his contemporaries, and would be taken up by the tradition leading to both Johannes Kepler and René Descartes. In his Perspectiva(Opus maius, Part Five) and De scientia experimentali(Opus maius, Part Six), he outlined a sketch for a scientific method, one that takes Optics as the model for an experimental science. In fact, Bacon and his contemporaries succeeded in the endeavor to have Perspectiva added to the four traditional quadrivium university subjects: arithmetic, geometry, astronomy, and music.

Opus maius, Part Four, deals with mathematics and the applications of mathematics. Bacon presented reasons for a reduction of logic to mathematics and saw mathematics as the key to an understanding of nature. Clearly, he was proclaiming the usefulness of mathematics for knowledge. He was not doing mathematical theory. Following his abbreviation of the De multiplicatione specierum which shows how mathematics might be applied to physics, he dealt with the application of astronomy/astrology to human affairs, the uses of mathematics in religious rites as in chronology, music, symbolism, calendar reform, geographical knowledge, and a resume of astrology. It used to be thought that Bacon was a Platonist in his view of the absolute priority of mathematics. That view has been seriously qualified. He did not reduce physics to mathematics. His explicit work on mathematics, the Communia mathematica, was not an exercise in mathematics: it was a presentation of the common notions that are important for a variety of mathematical practices. Bacon himself acknowledged those who were better mathematicians, namely, John of London, Pierre de Maricourt, and Campanus of Novara (Molland in Bacon, 1997). In general, Bacon was more interested in what mathematics can provide about knowledge of the world as an aid to missionary activity. He sent a map of the world to the pope.

Bacon was very interested in the applications of astronomy/astrology to human events. Although committed to a doctrine of freedom of the will, he held to a deterministic notion of causation in nature based on the Islamic authority on astrology, Abu Ma’ Shar (Albumassar) and on the De radiis of al-Kindi. And because he held to a doctrine of universal radiation in nature, he had to account for the influence of the heavens on the human body and hence on the human mind. Much of the polemic in his later works consisted of a justification of this interest in the face of traditional theological objections. He was also interested in alchemy. It was his determined interest in both of these areas that led to disagreement with his superiors in the Franciscan order, specifically, Bonaventure.

The Philosophy of Nature. Bacon’s treatise De multiplicatione specierum written before 1267 is closely related to the study of light, vision and perception in the Perspectiva. David C. Lindberg (1983a) noted that Bacon took Grosseteste’s physics of light, a development of al-Kindi’s universal radiation of force, out of its metaphysical background. He developed a universal doctrine of physical causation.

The use of species in this account is not that of Porphyry’s logic or the perceptual notion of likeness. It is “the force or power by which any object acts on its surroundings” (Lindberg, 1983a, p. Lv). It denotes “al-Kindi’s universal force, radiating from everything in the world to produce effects” (Lindberg, 1983a, p. Lv). As Bacon himself noted, “species [force, power] is the first effect of an agent. ... the agent sends forth a species into the matter of the recipient, so that, through the species first produced, it can bring forth out of the potentiality of matter [of the recipient] the complete effect that it intends” (Lindberg, 1983a, pp. 6–7). This was a universal theory of natural causation as the background for Bacon’s philosophy of vision and perception. Most importantly, species is a uni-vocal product of the agent. The first immediate effect of any natural action is definite, specific, and uniform. This production is not the imparting of an external form. The species is educed from the active potency of the matter (Lindberg, 1983a, p. 13).

This was a first attempt in the Latin world to provide separate domains for material and spiritual being. Natural causation occurs naturally according to regular processes or laws of nature. There is no spiritual being in the medium as was commonly taught by other Scholastic philosophers. No, for Bacon, universal causation was corporeal and material, and matter itself in not just pure potentiality but was rather something positive in itself. Hence, the general philosophy of nature prepared the theoretical ground for the specific application of mathematics to matters of vision and perception.

Perspectiva. Bacon, in his Perspectiva and related works, presented his model for a careful and detailed application of mathematics to the study of nature and mind. In imitation of the De aspectibus of Alhacen (Ibn al-Haytham), he provided an application of geometry to vision that within the terms of reference of his times was partly successful.

Bacon’s approach to vision and perception, however, was not an exercise in contemporary mathematical optics.

It should be seen as the sketch of a philosophy of perception and mind. These topics constitute Part One and a section of Part Two. The text then opens onto a consideration of direct, reflected and refracted vision, and ends with the application of geometrical models for moral and religious considerations.

Part One and Part Two, distinction one and two deal with the structure of the eye, problems of vision and visual errors. The aim is psychological and epistemological, that is, to set out the conditions for certifiable or verifiable and certain perception. The theory of the eye is taken from the Galenic tradition handed on by Constantine the African’s translation of Hunyan ibn Isaq and from Avicenna and Ibn al-Haytham. For this tradition, vision occurs when the crystalline humor is altered by the intromission of visual species from the object. Vision is completed when the species proceeds through the vitreous humor to the optic nerve and through this to the common nerve. It is here that a common visual judgment is made. Bacon followed Ibn al-Haytham and imposed a geometrical model on the eye. Using this model, Bacon was able to give a geometrical account of radiation through the eye. How then does one avoid confusion in vision and gain verifiable clarity? For Bacon, the perpendicular ray was primary; the other rays were treated as cases of indirect vision. Yet, the rays were refracted in the rear surface of the crystalline humor.

Bacon was concerned with optical illusions, whether inverted images, magnification, vision of distant objects, the moon illusion, and such matters. He attempted to solve in a rational and experimental manner the puzzles found in Ptolemy, Ibn al-Haytham, and others. Still, he was a child of his sources. These do not provide him with the more advanced data and mathematical method that would be characteristic of the seventeenth century. Rather, Bacon provided a functional qualitative geometry of the eye and vision. He was committed to an intromission theory of vision but he combined it with an extramission theory of vision that avoided the anthropomorphisms of earlier theories. He used the extramission theory mainly to emphasize the active role of the eye in vision.

In Parts Two and Three, he was to a certain extent successful in applying geometry to problems of direct, reflected, and refracted vision. He moved the study of these matters to a new level. The geometrical arguments were worked out with careful diagrams and various appeals are made to experimental conditions. What are these conditions? Some of them are simple thought experiments or even reports of experiments (actual or imaginary) from earlier writers. It seems clear, however, that Bacon himself did experimental work with pinhole images, lenses, and discrete observations. This did not lead to a pure geometrization of nature and he inevitably fell back on physical, perceptual, and metaphysical arguments. One might argue that he lacked the notion of infinity that is present in modern geometry.

Bacon introduced another important item for science. He refers to the laws of reflection and refraction as leges communes nature. For Bacon in his account of nature in Communia naturalium and the later works in general, a general law of nature governed universal force. This universal law of nature is imposed on a world of Aristotelian natures. This notion would have a significant future in experimental science.

Bacon ended Part Three with an account of how a better understanding of the phenomena of nature could lead to a more accurate knowledge of natural phenomena mentioned in scripture. He found in visual phenomena significant metaphors and analogies for use in moral and religious teaching. Direct evidence of Bacon’s influence here in making science available for an educated public is seen in the use of his work by Pierre de Limoges in his influential work De oculo morali(On the moral eye), written in Paris between 1275 and 1289. MS Paris, BN Lat. 7434 owned by Pierre de Limoges contains an early copy of Bacon’s Perspectiva. All of this suggests Pierre de Limoges as a very early reader of Bacon’s works.

De scientia experimentali. Presupposing the Perspectiva, Bacon in De scientia experimentali and in related works on the halo and on burning mirrors situated this new scientific practice as a desired area of study in the medieval university. Starting from Aristotle’s account of empeiria(experience), Bacon argued that logical argument alone is not sufficient for the verification of things. Even arguments that have their origins in experience will need to be verified by means of an intuition of the things in the world. He distinguished natural scientific argument from moral and religious mystical intuition, although he did allow for the notion of a revealed intuition in science.

His aim was to provide a method for science, one that was analogous to the use of logic to test validity in arguments. This new practical method consisted of a combination of mathematics and detailed experiential descriptions of discrete phenomena in nature. It would be distinguished from the conjurations of magic and from religious belief. It would also be different from philosophy of nature and from broad optical knowledge. These two areas are important for broad theory, but according to Bacon, they do not provide access to minute, detailed experiments. Nevertheless, for his description of the first example of an experimental science, the study of the rainbow, Bacon was dependent on Aristotle, Seneca, and Avicenna.

His own important contribution is to be found in his calculation of the measured value of forty-two degrees for the maximum elevation of the rainbow. This was probably done with an astrolabe, and in this, Bacon advocated the skillful mathematical use of instruments for an experimental science. That Bacon had mathematical competence in this field can be seen in his account of the Halo(Duhem edition of Opus tertium) and in his complex arguments in De speculis comburentibus. Bacon took up Grosseteste’s theory of refraction and tried to work out the difficulties. Important here is his emphasis on the role of individual drops of water for the process of reflection and refraction. A correct account of the rainbow would appear some forty years after Bacon in the De iride of Theodoric of Freiberg.

A second task for experimental science was the discovery by experience alone of instruments (armillary sphere), new medical cures, chemical discovery, and military technologies. An important item here is the discovery of magnetism. It would seem that Bacon was reporting on the actual experimental work of Magister Petrus Peregrinus, author of De magnete, who is lauded in the Opus tertium as the only worthwhile experimentalist at Paris. Bacon has been lauded down the centuries for his medical learning, but recent scholarship limited the number of works attributed to Bacon. Still, it is important here to note that he did draw on medical practice to set out rules and procedures that, in a nonscholastic manner, would lead to a more experimental approach to nature. The third task was that of the prognostication of the future on the basis of astronomical or astrological knowledge.

The conclusion to the De scientia experimentali is important. Bacon presented the ideal of the philosophical chancellor who will organize science and its technological products for the benefit of the Res publica Christiana. In this, he was influenced by the important Mirror of Princes from the Islamic World, the Sirr-al-‘asrar (Secretum secretorum, Steele ed. [1909–1940, Vol. 5]). Stewart C. Easton proposed that this work was the guiding vision for Bacon’s reform of science. Steven Williams argued (1994) that Bacon completed the edition of this work after his return to Oxford c. 1280. Still, there is much cross-reference between this work and Bacon’s writings in the 1260s.

David C. Lindberg has given a succinct summary of Bacon’s model for an experimental science (Bacon, 1997). He saw four main aspects. First, Bacon’s theories of perspectiva were not his own creation. He took the best available materials from Greek and Islamic scholars and produced his own synthesis. Second, there is much evidence that Bacon himself did mathematical work and experiments with visual phenomena such as pinhole images and the measurement of the visual field. Third, as seen above, Bacon correctly calculated the maximum degree of elevation for the rainbow. Fourth, the experiments in Bacon, especially in the Perspectiva, served theoretically significant functions. It supplied observational data that required explanation in terms of a given optical theory. The usual role of experiment in Bacon is to “confirm, refute or challenge theoretical claims” (Bacon, 1997, p. 271).

One might have expected Bacon to have given equal treatment to astronomy, but in this field he was a child of his time. He reported on the accounts of Aristotle, Ptolemy, and Alfraganus (Steele ed., Vol. 4). He discussed the pros and cons in a scholastic manner but did not advance the field in the manner that he did for Perspectiva. Bacon’s Moralis philosophia (Opus maius, VII) concerns philosophy of religion, social philosophy, a theory of the virtues, an astrological sociology of religion and cultures, and an account of argument and rhetoric.

Roger Bacon had an immediate influence on early fourteenth-century philosophers such as John Duns Scotus and William of Ockham especially in terms of the role of the doctrine of species in epistemology, and in matters relating to semantics and semiotics (see Tachau, 1998). He would also seem to have been read by members of the Merton School. It was in the late Middle Ages that Roger Bacon came to be seen as a hero for English medicine. Reduced to a figure of comedy in the late sixteenth century, his manuscripts were recovered by John Dee and Sir Kenelm Digby. His scientific works were first published in the early seventeenth century as a result of the Rosicrucian interest in science. The Opus maius was first published in 1733. Roger Bacon’s works began to be studied with the new historical interest in medieval texts in the nineteenth and early twentieth centuries.



Opera quaedam hactenus inedita (=Opus tertium, Opus minus, Compendium studii philosophiae, Epistola de secretis operibus Artis et Naturae, et de nullitate Magiae). Edited by John S. Brewer. London, 1859. Reprint, Nendeln, Lichtenstein: Kraus Reprint, 1965.

The Greek Grammar of Roger Bacon and a Fragment of His Hebrew Grammar. Edited by Edmund Nolan and Samuel A.

Hirsch. Cambridge, U.K.: Cambridge University Press, 1902.

Un fragment inédit de l’Opus tertium de Roger Bacon. Edited by Pierre Duhem. Florence, Italy: Quarrachi, 1909.

Opera hactenus inedita Rogeri Baconi(Vols. 1–16). Edited by Robert Steele, Ferdinand M. Delorme, Andrew Little, et al. Oxford: Clarendon Press, 1909–1940.

Fr. Rogeri Bacon Compendium Studii Theologiae. Edited by Hastings Rashdall. Aberdeen, U.K.: Aberdeen University Press, 1911.

Roger Bacon Essays. Collected and edited by A. G. Little. Oxford: Clarendon Press, 1914. These essays, some on Bacon’s science, are still valuable.

“Les Summulae dialectics de Roger Bacon.”Archives d’Histoire Doctrinale et Litteraire du Moyen Age53. Edited by Alain de Libera (1986): 139–289; 54 (1987): 171–278.

Roger Bacon and the Sciences: Commemorative Essays. Edited by Jeremiah Hackett. New York: Brill, 1997. (Studien und Texte zur Geistesgeschichte des Mittelalters, Band LVII): Woodward & Howe on Geography/Cartography; Van Deusen on Music; Molland on Mathematics; Hackett on Astrology; Lindberg on Light, Vision and Universal Radiation of Force; Newman on Alchemy; Hackett on scientia experimentalis; Getz on Roger Bacon and Medicine; Williams on the Secretum secretorum.

Roger Bacon and Aristotelianism. Edited by Jeremiah Hackett. Vivarium 35 (September 1997): 129–320. This special edition of the journal is a study of the place of Bacon in the reception of Aristotle. See papers by Marmo, Trifogli, Donati, Wood, Noone, Long, Hackett.


Adamson, Robert. Roger Bacon: The Philosophy of Science in the Middle Ages. Manchester, U.K.: J.E. Cornish, 1876.

Bagliani, A. Paravicini. “Ruggero Bacone, autore del De ratardatione accidentium senectutis?” in Studi Medievali, 3rd ser., 28 (1987): 707–728.

Ebbesen, Sten. “The Dead Man Is Alive.” Synthese40 (January 1979): 43–70.

Fredborg, K. M., Lauge Nielsen, and Jan Pinborg, eds. “An Unedited Part of Roger Bacon’s Opus Maius: De signis.” Traditio 34 (1978): 75–136.

Hedwig, Klaus. “Roger Bacon’s Scientia experimentalis.” In Philosophen des Mittelalters, edited by Theo Kobush. Darmstadt, Germany: Primus, 2000.

Lindberg, David C. Theories of Vision from Al-Kindi to Kepler. Chicago: University of Chicago Press, 1978.

———, ed. De multiplicatione specierum and De speculis comburentibus. Oxford: Clarendon Press, 1983a.

———.Studies in the History of Medieval Optics, London: Variorum Reprints, 1983b.

———. Perspectiva. Oxford: Clarendon Press, 1996.

“Lines of Influence in Thirteenth Century Optics: Bacon, Witelo, and Pecham.” Speculum46 (January 1971): 66–83.

Maloney, Thomas S. “The Semiotics of Roger Bacon,” Medieval Studies 45 (1983): 120–154.

———. “The Extreme Realism of Roger Bacon.” Review of Metaphysics 38 (June 1985): 807–837.

———, ed. Compendium studii theologiae. Leiden, Netherlands: Brill, 1988.

Massa, Eugenio, ed. Rogeri Baconis Moralis Philosophia. Zürich: Thesaurus Mundi, 1953.

Matthews, Gareth B. “A Medieval Theory of Vision.” In Studies in Perception: Interrelations in the History of Philosophy and Science, edited by Peter K. Machamer and Robert G. Turnbull. Columbus: Ohio State University Press, 1978.

Molland, A. G. “Roger Bacon as Magician.” Traditio 50 (1974): 445–460.

———. “Roger Bacon and the Hermetic Tradition in Medieval Science.”Vivarium 31 (1983): 140–160.

———. “Roger Bacon’s Appropriation of Past Mathematics.” In Tradition, Transmission, Transformation: Proceedings of Two Conferences on Pre-Modern Science Held at the University of Oklahoma, edited by F. Jamil Ragep, Sally P. Ragep, and Steven Livesey. Leiden, Netherlands: Brill, 1996.

———. “Roger Bacon’s De laudibus mathematicae: A Preliminary Study.” In Texts and Contexts in Ancient and Medieval Science: Studies on the Occasion of John E. Murdoch’s Seventieth Birthday, edited by E. Sylla and M. McVaugh. Leiden, Netherlands: Brill, 1997.

Newman, William R. “The Alchemy of Roger Bacon and the Tres espistolae Attributed to Him,” in Comprendre et maitriser la nature au moyen age: mélanges d’hisgtoire offerts a Guy Beaujouan, Geneva: Droz, 1994.

Richard Rufus of Cornwall, In Physicam Aristotelis, edited by Rega Wood. Auctores Britannici medii aevi, 16. Oxford: Oxford University Press for The British Academy, 2003.

“Roger Bacon and the Reception of Aristotle in the Thirteenth Century: An Introduction to His Criticism of Averroes.” In Albertus Magnus and the Beginnings of the Medieval Reception of Aristotle in the Latin West, edited by Ludger Honnefelder, Rega Wood, Mechthild Dreyer, et al. Münster, Germany: Aschendorff Verlag, 2005.

Tachau, Katherine H. Vision and Certitude in the Age of Ockham: Optics, Epistemology and the Foundations of Semantics 1250–1350. Leiden, Netherlands: Brill, 1988.

Thorndike, Lynn. “Roger Bacon and Experimental Method in the Middle Ages.” Philosophical Review23 (1914): 271–298.

———. “The True Roger Bacon I,” and “The True Roger Bacon II.” The American Historical Review 21 (1916): 237–257, 468–480.

Whewell, William. History of the Inductive Sciences from the Earliest Times to the Present Times, Vol. 1. New York, 1859.

Williams, Steven J. “Roger Bacon and His Edition of the Pseudo-Aristotelian.” Secretum secretorum, Speculum69 (1994): 57–73.

Jeremiah, Hackett

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Roger Bacon

Roger Bacon

The medieval English philosopher Roger Bacon (ca. 1214-1294) insisted on the importance of a so-called science of experience, or "scientia experimentalis." In this respect he is often regarded as a forerunner of modern science.

Little is known about the details of Roger Bacon's life or about the chronology and motivation of his major works, the Opus majus, the Opus minus, and the Opus tertium. It appears that he was born in Ilchester, Somerset. At 13 he entered Oxford University, where he spent 8 years. Contrasting himself to other scholastics who received only a baccalaureate in the arts and then moved on to theology, Bacon took delight in having the advanced arts degree.

In the 1240s, perhaps in the early years of the decade, Bacon lectured at the University of Paris on the works of Aristotle. During this period he also wrote three works on logic. Within relatively few years there were three important events in Bacon's life: his return to England from France, the awakening of his scientific interests, and his entry into the Franciscan order.

A Universal Science

Early in his empirical pursuits Bacon envisioned a universal science which would promote the spread of Christianity, prolong life, aid health, and form a synthesis between theology and the science of experience. Theology for Bacon was more or less biblical theology, not the scholastic theology based on the Sentences of Peter Lombard, which Bacon may have known only superficially. He praised science as being "most beautiful and most useful." Bacon had other reasons for urging Christians to take up a science of experience. In many respects his age had an apocalyptic character, and there was considerable belief that a struggle with the antichrist was imminent. Bacon saw a science of experience as a Christian weapon for the fray.

It is quite likely that Bacon became a Franciscan in 1252. By Bacon's time, as even more so during the following century, the work begun by St. Francis had posed problems for his followers. Franciscans were required to take a vow of poverty, but their work had swelled to such size and importance that it was impossible to continue it unless the order owned or at least administered property and other possessions. However, the acquisition of property by the Franciscan order was seriously questioned by a group of friars who claimed a literal allegiance to St. Francis. Bacon joined this group.

Moreover, during this very period of struggle over the vow of poverty, the new orders, Dominican as well as Franciscan, were being attacked by the secular clergy, whose power was being diminished as the religious clergy grew in numbers and influence.

Period of Confinement

About 1257 Bacon was taken from England to France and, for unknown reasons, underwent some kind of confinement, perhaps even an imprisonment, in a French monastery. One theory is that his scientific interests made him suspect, but it is more likely that his views on Franciscan life proved unpopular with the friars in England. Actually, there are no grounds for thinking that this confinement had anything to do with an alleged conflict between science and religion.

During his period of confinement Bacon wrote his greatest works: the Opus majus, the Opus minus, and the Opus tertium. Differences among scholars concerning the order and purposes of these works underscore once again the many unknowns concerning Bacon's life. It seems that he intended to write a treatise on the sciences but soon realized the magnitude of such a task. Instead, he composed what is now known as the Opus majus, in which he made use of materials already written, added new material, and climaxed the work with a section on moral theory. With respect to the sciences, the overall tone of the Opus majus is a rhetorical plea, attempting to persuade the pope about the importance of experimental knowledge. There is no evidence that Bacon made any important contribution to science and much evidence that he was, instead, a reader, writer, and rhetorician in behalf of science. Concerning the Opus minus, a convincing theory is that it was written while the Opus majus was still in the hands of copyists and Bacon was reflecting on his omissions from the earlier manuscript. The Opus minus is thus a supplement to the Opus majus. The Opus tertium may well have been an expansion of what began as a preface to the earlier two works.

Observations and Writings

In many ways Bacon was ahead of his time. His works mention flying machines, self-driven boats, and an "instrument small in size, which can raise and lower things of almost infinite weight." He studied the heavens. He seems to have studied the refraction of light under experimental conditions, but in his so-called science of experience he did not make any known advances into what is today called physics; and he did not make any known practical inventions.

After the three works previously mentioned, Bacon wrote a great part of Communium naturalium, one of his finest works. He also wrote a Greek grammar and a Hebrew grammar, and in 1272 he published Compendium of the Study of Philosophy, in which the old, angry, polemical Bacon reemerges. It is possible that an imprisonment in the final years of his life stems from the Compendium, in which he claimed to see in the then-warring factions of Christendom the presence of the antichrist and in which he took in general the extreme view of Franciscan life identified with Joachim of Fiore.

The length of his imprisonment and the causes of his release are again matters of educated guesswork. He was free enough late in life to write Compendium of Theology. He was not imprisoned at the time of his death, which occurred in 1294 (according to one account, on June 11).

Further Reading

The best work on Bacon is Stewart C. Easton, Roger Bacon and His Search for a Universal Science (1952). See also John Henry Bridges, The Life and Work of Roger Bacon (1914); Theodore Crowley, Roger Bacon (1950); and E. Westacott, Roger Bacon in Life and Legend (1953). Appreciative discussions of Bacon are in A. G. Little, ed., Roger Bacon: EssaysContributed by Various Writers on the Occasion of the Commemoration of the Seventh Centenary of His Birth (1914). See also Lynn Thorndike, A History of Magic and Experimental Science (2 vols., 1923), and a chapter by Robert Steele, "Roger Bacon and the State of Science in the Thirteenth Century," in Charles Singer, ed., Studies in the History and Method of Science, vol. 2 (1921).

Additional Sources

Bridges, John Henry, The life & work of Roger Bacon: an introduction to the Opus majus, Merrick, N.Y.: Richwood Pub. Co., 1976.

Westacott, Evalyn, Roger Bacon in life and legend, Norwood, PA:Norwood Editions, c1953, 1978. □

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Bacon, Roger

Roger Bacon

Born: c. 1214
Ilchester, Somerset, England
Died: c. 1292
Oxford, England

English philosopher

The medieval English philosopher Roger Bacon insisted on the importance of a so-called science of experience. In this respect he is often thought of as a forerunner of modern science. Little is known for certain about the details of Roger Bacon's life or about the chronology of and inspiration for his major works.

Childhood, education, and university life

It appears that Bacon was born in Ilchester, Somerset, England. He was born into a noble family, although not a major one. In his youth he studied the works of the ancient Greeks as well as arithmetic, geometry, astronomy, and music. At thirteen years old he entered Oxford University, where he spent the next eight years. He eventually received an advanced arts degree.

In the 1240s, perhaps in the early years of the decade, Bacon lectured at the University of Paris, France, on the works of the ancient Greek philosopher Aristotle (c. 384c. 322 b.c.e.). During this period he also wrote three works on logic, or the study of how to reason correctly. Within relatively few years there were three important events in Bacon's life: his return to England from France, the awakening of his scientific interests, and his entry into the Franciscan order, the Christian group founded by St. Francis of Assisi (11821226).

A universal science

Early on Bacon had the idea for a universal, or general, science that would promote the spread of Christianity, prolong life, aid health, and unite theology (the study of God and His ways) and the science of experience. He praised science as being "most beautiful and most useful." Bacon had other reasons for urging Christians to take up a science of experience. At the time there were many who believed that a struggle with the antichrist (or great evildoer whose arrival on Earth was predicted in the Bible) was near at hand. Bacon saw a science of experience as a Christian weapon for the fight.

It is quite likely that Bacon became a Franciscan in 1252. By Bacon's time the work begun by St. Francis had posed problems for his followers. Franciscans were required to take a vow of poverty, but their work had grown to such size and importance that it was impossible to continue it unless the order owned property and other possessions. The owning of property by the Franciscan order, however, was seriously questioned by a group of Franciscans. Bacon joined this group.

His works

About 1257 Bacon was taken from England to France and, for unknown reasons, underwent some kind of confinement, perhaps even an imprisonment, in a French monastery. One theory is that people questioned him because of his scientific interests, but it is more likely that his views on Franciscan life proved unpopular with some Franciscans in England.

During this period of confinement Bacon wrote his greatest works: Opus majus (major work), Opus minus (minor work), and Opus tertium (third work). Disagreements among scholars concerning the order and purposes of these works show once again the many unknowns concerning Bacon's life. In Opus majus he made use of scientific materials already written, added new material, and included a section on moral theory. With respect to the sciences, the overall tone of Opus majus is a plea, attempting to persuade the pope (the head of the Catholic Church) about the importance of experimental knowledge.

After the three works, Bacon wrote a great part of Communium naturalium (general principles of natural philosophy), one of his finest works. In 1272 he published another book on the study of philosophy in which the old, angry, argumentative Bacon reemerges. In it he claimed to see the presence of the antichrist in the then-warring Christian groups, and he took in general the extreme view of Franciscan life. It is also possible that an imprisonment in the final years of his life stems from this book.

Science's early friend

In many ways Bacon was ahead of his time. His works mention flying machines, self-driven boats, and an "instrument small in size, which can raise and lower things of almost infinite weight." He studied the heavens. He seems to have studied the refraction (bending) of light under experimental conditions. However, in his so-called science of experience he did not make any known advances in what is today called physics, nor did he make any known practical inventions. There is no evidence that Bacon made any important contribution to science, but there is much evidence that he was instead a reader, writer, and champion of science.

For More Information

Bridges, John Henry. The Life and Work of Roger Bacon. London: Williams & Norgate, 1914.

Easton, Stewart C. Roger Bacon and His Search for a Universal Science. Westport, CT: Greenwood Press, 1952.

Westacott, Evalyn. Roger Bacon in Life and Legend. Folcroft, PA: Folcroft Library Editions, 1974.

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Bacon, Roger (ca. 1220-1292)

Bacon, Roger (ca. 1220-1292)

Versatile British scientist and philosopher around whom accumulated many legends of occult powers. He was born near Ilchester in Somerset, England. He entered the Order of St. Francis and studied mathematics and medicine in Oxford and Paris. Returning to England, he devoted his attention to philosophy and also wrote Latin, Greek, and Hebrew grammars.

Bacon was a pioneer of astronomy and, being acquainted with the properties of lenses, may have foreshadowed the telescope. In the mechanical sciences, Bacon envisioned boats propelled without oars, cars that move without horses, and even machines that fly in the air. In the field of pure chemistry, Bacon's name is associated with the making of gunpowder, for even if the discovery cannot be wholly attributed to him, at least his experiments with niter paved its way.

His study of alchemy naturally led him to a belief in the philosophers' stone, by which gold might be purified to a degree impossible by any other means, and also to a belief in the elixir of life, which, along similar principles of purification, might fortify the human body against death. Thus man could become practically immortal, and by knowledge of the appropriate herbs or by acquaintance with planetary influences, he could experience the same consummation.

Ahead of his time, Bacon was looked on with considerable suspicion, which eventually led to persecution. The brethren of his order practically cast him out, and he was compelled to retire to Paris and to submit to a régime of repression. A prolific author, he was forbidden to write, and it was not till 1266 that Guy de Foulques, the papal legate in Englandlater Pope Clement IVheard of Bacon's fame and invited him to break his enforced silence. Bacon hailed the opportunity and in spite of hardship and poverty, he finished his Opus Majus, Opus Minus, and Opus Tertium.

Clement seemed to approve of these works, because Bacon was allowed to return to Oxford, where he continued his scientific studies and the composition of scientific works. He attempted a compendium of philosophy which still exists in part, but its subject matter displeased the ruling powers, and Bacon's misfortunes began afresh. His books were burned, and again he was thrown into prison. He remained there for 14 years, during which time he probably continued to write. About 1292 he was given his liberty, however he is believed to have died shortly thereafter.

Of Bacon's works, which were numerous, many still remain in manuscript and about a dozen have been printed at various times. Many are obscure treatises on alchemy, but the works he wrote by invitation of Clement are the most important. The Opus Majus is divided into six parts treating of the causes of error, the relation between philosophy and theology, the utility of grammar, mathematical perspective, and experimental science. The Opus Minus, of which only part has been preserved, was intended to be a summary of the former work. The Opus Tertium, though written after the other two, actually serves as an introduction to them and is in part supplementary to them. These works, large though they be, were intended to be fore-runners of an even greater work to examine the principles of all the sciences; however, this latter endeavor was probably little more than begun.

Although much of Bacon's work and many of his beliefs reflect the outlook of his period, in his devotion to the experimental sciences he stood far above his peers. This has led to an accretion of legendary material around Bacon's name, by virtue of which he has been regarded as a great magician. In the sixteenth century, when the study of magic was pursued with increased zeal, Friar Bacon became the subject of a popular book, entitled The History of Friar Bacon, and the subject of an often-performed play by Robert Greene, one of the dramatists of the age. The greater part of his history of Friar Bacon is evidently the invention of the writer, who lived in the time of Queen Elizabeth. He adapted some of the older traditions and fleshed out the narrative with fables taken from books of the time, including stories about two other legendary occult conjurers, Friars Bungay and Vandermast. The recital is further enlivened with the pranks of Bacon's servant, Miles.


Bacon, Roger. The Mirror of Alchemy. Los Angeles: Press of the Pegacycle Lady, 1975.

. The Opus Majus of Roger Bacon. 2 vols. Philadelphia: University of Pennsylvania Press, 1928.

. Roger Bacon's Philosophy of Nature: A Critical Edition. Oxford: Clarendon Press, 1983.

Bridges, John Henry. The Life and Work of Roger Bacon. 1914. Reprint, Merrick, N.Y.: Richwood, 1976.

Easton, Stewart C. Roger Bacon and His Search for a Universal Science. Westport, Conn.: Greenwood Press, 1970.

Little, A. G. Roger Bacon Essays. Oxford: Clarendon Press, 1914.

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Bacon, Roger

Roger Bacon, c.1214–1294?, English scholastic philosopher and scientist, a Franciscan. He studied at Oxford as well as at the Univ. of Paris and became one of the most celebrated and zealous teachers at Oxford. Bacon was learned in Hebrew and in Greek and stressed the value of knowing the original languages in the study of Aristotle and of the Bible. He may also have known Arabic; his own philosophy drew upon Arab Aristotelianism as well as upon St. Augustine. He had an interest far in advance of his times in natural science, in controlled experiments, and in the accurate observation of phenomena. "It is the intention of philosophy," he said, "to work out the natures and properties of things." He declared that mathematics was the gateway to science, and experience, or verification, the only basis of certainty. This belief in experience as a guide to the outer world was, however, not divorced from theology; wisdom and faith were to him one. His writings were numerous. Three of his most important works were written for Pope Clement IV in one year (1267–68)—the Opus majus (tr. 1928), the Opus minor, and the Opus tertium. He was deeply interested in alchemy, an interest that may account for his being credited by his contemporaries with great learning in magical practices. He was long credited with the invention of gunpowder (because of a formula for gunpowder that appeared in a work attributed to him). A manuscript in cipher, discovered in the 20th cent. and attributed to him, would make Bacon the first man to have observed spiral nebulae through a telescope and to have examined cells through a microscope; but considerable doubt has been cast on the original date and the authenticity of the manuscript. Earlier editions of his major works were supplemented by an edition of his hitherto unedited works in various fascicles by Robert Steele and others (1909–35).

See A. G. Little, ed., Roger Bacon Essays (1914, repr. 1972); biography by F. Winthrop Woodruff (1938); studies by T. Crowley (1950) and S. C. Easton (1952, repr. 1971).

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Bacon, Roger

Bacon, Roger (c.1214–92). Philosopher. A Franciscan friar, much of Bacon's life is obscure, but he was born in Somerset and probably studied at Oxford before teaching in Paris. From c.1250–7 he was again in Oxford but his Franciscan superiors returned him to Paris, where he was under a cloud and in confinement. In 1265 Pope Clement IV asked him to prepare a treatise on the knowledge of the day. This high patronage did not last, for Clement died in 1268, and Bacon was soon in trouble again. His Opus majus, dating from the 1260s, attacked authority and sophistry and has been hailed as a foundation work in modern science. Bacon laid stress on useful knowledge, on ascertaining facts, and on the need for experimentation. He proved that air is necessary for combustion, and his prophecies included flight and submarine travel. His work in alchemy gained him a popular reputation as a magician, exploited by Robert Greene in Friar Bacon and Friar Bungay (c.1590). This showed Bacon at Brasenose College making a brazen head which would prophesy, ‘read a lecture in philosophy’, and build a brazen wall to keep England safe.

J. A. Cannon

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Bacon, Roger

Bacon, Roger (c.1214–92). Franciscan philosopher. Born in England, he was one of the first to show interest in Aristotle's scientific works, then becoming known in the West. He devoted himself to languages, mathematics, and experimental science, and became a Franciscan. Later, in Paris, he wrote his encyclopaedic work, the Opus Maius, for Pope Clement IV, after whose death in 1268 he came under suspicion of novelty and dangerous doctrine.

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