Early Career

Roger Bacon was born into a prosperous English family in an unknown place and at an unknown date, variously estimated to be about 1210, about 1214, or about 1220.1 We know nothing of Bacon's early education, but it is evident that his university studies were pursued at Oxford and Paris. After earning the master of arts degree at one or the other of those two universities (usually conjectured to be Oxford), Bacon taught in the faculty of arts at Paris, lecturing principally (but not exclusively) on Aristotle's libri naturales.2 This teaching apparently took place in the early to mid-1240s.3

Bacon claims to have seen Alexander of Hales, who died at Paris in 1245, with his own eyes. This provides us with our first firm chronological anchor. There is great uncertainty about Bacon's movements in the late 1240s and 1250s. All we really know is that in 1251 he was in Paris, where he witnessed the uprising of the Pastoreaux rebels.

Whatever the details of his movements, it appears that Bacon experienced a dramatic broadening of his philosophical outlook in the late 1240s, breaking out of the confines of Aristotelian philosophy and devoting himself for about two decades to the study of a variety of other sources available in recent translations from Greek and Arabic. These studies may have been inspired by the example of Robert Grosseteste (ca. 1168-1253), who was never Bacon's teacher (contrary to claims that have been made), but to whose works Bacon clearly had access. The outcome of these studies was a broad mastery of the materials that Bacon would eventually write about under the rubrics of mathematical and experimental science, including

  • geography
  • alchemy
  • astronomy
  • astrology
  • meteorology
  • perspectiva (optics).4

Bacon's claim to have spent £2000 on books, instruments, and other scholarly necessities must apply to this period:

For during the twenty years in which I have labored especially in the pursuit of wisdom, abandoning the opinions of the vulgar, I have spent more than two thousand pounds on these studies, for books of secrets, various experiments [experientias], languages, instruments, tables, and other things.5

Bacon becomes a Franciscan

At an unknown date (circa 1257), Bacon joined the Franciscan Order. We do not know why he joined, but by the middle of the thirteenth century there was nothing surprising about an arts master entering one of the mendicant orders. Bacon was undoubtedly attracted by the prestige of the Franciscan Order for learning and piety and by the example of predecessors, such as Adam Marsh (whom he greatly admired). We may safely assume that he believed that in some way becoming a friar would enhance his studies or advance his agenda for the reform of Christendom. Of course, there may have been other motivating factors of which we have no knowledge.

Bacon's career as a Franciscan friar did not prove to be an entirely happy one, which is one reason why the question of Bacon's membership in the Franciscan Order has attracted scholarly commentary. He may have undergone a period of illness after entering the Order. He complained later that his superiors and brothers kept him "under close guard and would not permit anyone to come" to him,6 perhaps because he had broken rules of the Order by composing books without permission and appealing for patronage outside the Order. At some date before 1265 he was transferred back to Paris, perhaps for closer watching. We find him in Paris about this time, soliciting patronage from Cardinal Guy de Foulques.

In February, 1265, Guy de Foulques was elevated to the papal throne as Clement IV, and Bacon (no doubt determined to take advantage of this turn of fortune) renewed his request for support. Under the mistaken impression that at least some of Bacon's works were finished, Clement responded to this solicitation by asking Bacon to send the relevant works, including his "remedies for the critical problems to which you have recently called our attention."7

Bacon flew into action, but soon realized that in the available time he would be unable to write the ambitious work originally planned – a full statement of his ideas on learning and its applicability to the problems confronting Christendom. Instead, he assembled various existing pieces, adding new material where necessary to achieve a measure of continuity, and dispatched the product of these efforts – the Opus maius (including the Perspectiva), the Opus minus, and De multiplicatione specierum (in two versions) – to the Pope late in 1267 or early in 1268.8 We can infer that these works reached the papal court from the fact that the optical material contained in them influenced Witelo, a Polish scholar associated with the papacy. But we do not know what further immediate influence they may have had.9

Later years and works

The remaining years of Bacon's life are clouded in obscurity. He continued to write, completing the Communia naturalium and composing the Compendium studii philosophie.10 Recently Steven Williams has argued (against received opinion) that Bacon's new edition of the pseudo-Aristotelian Secretum secretorum was also a product of these later years.11

There is a fairly late and (in my judgment) questionable tradition to the effect that Bacon underwent a period of imprisonment. If this is so, as some believe, it is unlikely to have had anything to do with Bacon's scientific ideas, which were not at all dangerous (with the possible exception of his pro-astrological stance). Bacon composed his Compendium studii theologie in 1292,12 and he may be presumed to have died in 1292 or soon thereafter.

Bacon's Works on the Science of Perspectiva (Optics)

Of all of the topics within this body of learning so vitally important to the church, the one Bacon commanded most fully and wrote on most copiously, effectively, and influentially was the science of perspectiva (optics). Three treatises contain the bulk of Bacon's perspectival effort. The broadest of the three in terms of philosophical scope, and possibly the earliest, was his De multiplicatione specierum (best translated On the Propagation of Likenesses).13 In this work he developed an entire philosophy of nature based on the belief that all natural agents act through the propagation or multiplication of their species or likenesses to recipients.

Since the propagation of light is the most accessible example of this phenomenon, De multiplicatione specierum amounts to a major statement of many of the fundamental principles of perspectiva.14 We have no means of dating Bacon's composition of De multiplicatione specierum. It is a product of the studies that he undertook in the late 1240s and continued (by his account) for the next two decades. Since it is cited several times in the Perspectiva, we can be certain that it antedated (or, at the very least, was contemporary with) the latter work. Easton dates De multiplicatione specierum to about 1262 - a plausible guess.15

Whereas De multiplicatione specierum deals with broad foundational principles, Bacon's Perspectiva offers a comprehensive account of the particulars of the science of perspectiva--theories of light, color, vision, and a variety of peripheral topics. It may have been written about 1263, as Easton guesses.16

Finally, Bacon wrote a shorter tract, De speculis comburentibus (On Burning Mirrors), an exhaustive and tightly argued mathematical analysis of the modes of propagation of light. He wrote it as a commentary on the final proposition of Euclid's De speculis, applied to such phenomena as burning mirrors and radiation through small apertures. Like Bacon's other perspectival works, it is difficult to date. We know that it was completed before the mid-1270s, since it influenced John Pecham's Perspectiva communis. It appears to me that its theory of radiation through small apertures represents an advance over the comparable theories presented in Bacon's De multiplicatione specierum and Perspectiva. If these conclusions are correct, De speculis comburentibus was probably written between approximately 1263 and 1274.17

Bacon was constantly reworking, or at least restating, his ideas on the multiplication of species and other perspectival topics. Besides the three works described above, he included perspectival material in his Communia naturalium, part IV of the Opus maius, the Opus tertium, and perhaps the Compendium studii theologie.18 Bacon also produced multiple versions of some of the treatises containing perspectival material. There is evidence that De multiplicatione specierum existed in three versions, two of which still exist.19 And Bacon appears to have revised at least certain portions of the Perspectiva.20

Bacon's authorship of the three major perspectival works has never been questioned and is not in doubt. Stylistic and doctrinal similarities, as well as cross-references, identify them as achievements of the same person. Moreover, the three perspectival works can be linked to other works in the Baconian corpus by explicit citations and similarities in style and content. All of this optical activity is consistent with our knowledge of Bacon's career more generally. Bacon's Opus tertium, for example, provides a running commentary on the Opus maius, to which the Perspectiva belongs.21 Manuscript copies of De multiplicatione specierum and the Perspectiva frequently identify Bacon as their author.22

Bacon's Delight in the Science of Perspectiva

The science of perspectiva was devoted to light, color, and vision.23 It was one of the new subjects taken up by Bacon in the late 1240s, and it became one of his major preoccupations. On several occasions Bacon called attention to the merits of this science. He began his treatise on Perspectiva (part V of the Opus maius) by promising that

if our deliberations to this point have been beautiful and delightful, the matters now to be considered are far more beautiful and delightful, because we take special delight in vision and because light and color have singular beauty, exceeding that of the other things that are conveyed to our senses.24

But it is not simply the beauty and delight furnished by light, color, and vision that recommend them to us. They also possess epistemic superiority. It is through vision that

we experience everything in the heavens and on earth. For celestial objects are observed by means of visual instruments, as Ptolemy and other astronomers teach, as are things generated in the air, such as comets, rainbows, and the like; for their altitude above the horizon, their size, shape, and number, and everything in them are certified by means of vision aided by instruments. Through vision we also experience things here on earth, for regarding this world the blind can have no experience worthy of the name.25

Bacon continues, arguing that although beliefs may be gained through our sense of hearing (for example, by listening to our teachers), it is only through vision that we can "experientially test" what we have thus come to believe.

Bacon believes that a sign of this alleged superiority can be found in the existence of a separate science of perspectiva.

...if what is sought is easy, it is unnecessary to create a science [out of it]; likewise, if it is difficult but useless we do not create a science of it, since such effort would be foolish and futile. Furthermore, unless a subject were extraordinarily useful and contained many outstanding truths, there would be no need to construct a separate science of it; rather, we could treat it sufficiently along with other matters as part of a common science in a chapter or some portion of a book. But concerning sight alone, and not the other senses, have philosophers developed a separate science, perspectiva. It follows that the wisdom gained through vision must have a special utility, not found in the other senses.26

Bacon admits that a science more useful than perspectiva might exist. But none, he insists, "possesses utility of such charm and beauty."27

How Perspectiva Relates to Theology

All of this has been quite abstract and general. Bacon closes the Perspectiva with four chapters in which he looks at specific examples of the utility of perspectiva for theology or "sacred wisdom." Bacon makes four main points in these closing chapters.

  1. Successful biblical exegesis, leading to the full acquisition of divine truth, requires knowledge of all of the natural sciences. These sciences, in turn, depend on perspectiva for explanation, clarification, and certification.
  2. The science of perspectiva is directly applicable to scriptural exegesis, since "in divine scripture, nothing is dealt with as frequently as matters pertaining to the eye and vision...; and therefore nothing is more essential to [a grasp of] the literal and spiritual sense than the certitude supplied by this science."28
    • As an example of the latter, Bacon calls attention to Psalm 17:8, where the psalmist writes: "Preserve me, oh Lord, as the pupil of your eye." Bacon believes that we will never fully understand the meaning of this passage unless we grasp how the pupil is preserved, and only the science of perspectiva supplies that understanding.
  3. The science of perspectiva is a rich source of allegory applicable to spiritual truths. Bacon devotes substantial effort to demonstrating the allegorical possibilities, offering multiple examples.
    • Just as we see nothing corporeally without corporeal light, so it is impossible for us to see anything spiritually without the spiritual light of divine grace.29
    • Just as moderate distance of the [visible] object is required for vision of that object..., so the same thing is required spiritually, for remoteness from God through infidelity and a multitude of sins destroys spiritual vision....30
    • Just as physical vision is of three kinds (direct, refracted, and reflected), so spiritual "vision is direct in those who are perfect, refracted in those who are imperfect, and reflected in evildoers and whose who ignore God's commandments" - an account backed up by appeal to James 1:23 ("Now we see through a glass darkly...").
  4. The science of perspectiva offers access to technological wonders, which promise to equip the Christian commonwealth for battle against its enemies.
    • For example, "mirrors can be so constructed and so placed and arranged that one thing will appear to be as many as we choose." One man could thus be made to appear as an army, and one army as many armies. Such results, Bacon argues, will be "useful to friends and terrifying to enemies."31
    • Similar feats can be performed by use of the laws of refraction, "so that the mind of a mortal ignorant of the truth could not withstand them."32

Perspectiva and mathematics

Finally, it is important to note that Bacon classified perspectiva among the mathematical sciences and thus implicitly endowed it with all of the virtues of mathematics - which he took to be one of four sciences (in addition to experimental science, perspectiva, and linguistic accomplishment) so basic as to constitute the foundation of all others. "The gate and key of these [four] sciences," he argued,

is mathematics, which holy men discovered at the beginning of the world...and which has always been used by holy and wise men more than any other science....Knowledge of this science prepares the mind and elevates it to sure knowledge of all things, so that if one grasps the basics of wisdom concerning this science and applies them correctly to knowledge of other sciences, one will be able to know all things that follow, without error or doubt, easily and powerfully.33

Bacon demonstrated the intimate relationship between perspectiva and mathematics by devoting nearly ten percent of his discussion of the latter in part IV of the Opus maius to an analysis of topics belonging to the former.

Is Bacon's plea for the importance of mathematics and perspectiva to be taken at face value? Or should we dismiss it as mere rhetoric designed to persuade powerful ecclesiastics to patronize Bacon's ambitious intellectual program? Given the context, it is certain that Bacon would not have understated his case. But it does not follow that, in making the case, Bacon was insincere. It is well known that he was active in the widespread thirteenth-century effort to reclaim secular learning for Christendom by demonstrating that it could serve as the disciplined handmaiden of religion and theology. This was an expression of Bacon's commitment to the Augustinian ideal of philosophy in the service of religion.

Bacon's devotion to mathematics and its related subjects also demonstrates the refusal, not only by Bacon but also by large numbers of his contemporaries, to regard the classical tradition (that is, the materials newly translated from Greek and Arabic) as antagonistic to the Christian faith. In short, refusal to take Bacon's arguments at face value is part and parcel of the refusal to accept the medieval period for what it was. The opinion that discredits Bacon's arguments as mere rhetoric is the same opinion that foists modern (or, more exactly, Enlightenment) notions of incompatibility between religion and science onto the Middle Ages.

1. Lindberg, Bacon's Philosophy of Nature, pp. xv-xvi. But see Jeremiah Hackett's counter-argument in 'Scientia experimentalis: From Robert Grosseteste to Roger Bacon', pp. 66-76.

2. These lectures have been edited and published in the 16 fascicules of Bacon's Opera (Steele).

3. But See Hackett's argument, 'Scientia experimentalis', part I, for a date of birth about 1214 and a teaching career at Paris beginning about 1237.

4. For a list of Bacon's putative writings, with commentary and bibliographical data, see the Appendix to Little's Roger Bacon Essays, pp. 375-419.

5. Bacon, Opus tertium (Brewer), p. 59. On the expenses involved in research, see also ibid., pp. 34-38 (translated by Brewer in his introduction, pp. lxxv-lxxvii).

6. Easton, Bacon, p. 134.

7. Bacon, Opus maius, vol. 1, pp. 1-2, n. 1; Opus tertium (Little), p. viii.

8. Little, 'Bacon's Life and Works', p. 20.

9. On the reception of Bacon's works and their utilization by Witelo, see Lindberg, 'Lines of Influence in Thirteenth-Century Optics: Bacon, Witelo, and Pecham,' 72-75. On Witelo, see Agostino Paravicini Bagliani, 'Witelo et la science optique à la cour pontificale de Viterbe (1277)', Mélanges de l'école française de Rome (moyen-âge - temps modernes), 87 (1975), 425-53; Jerzy Burchardt, Witelo, filosofo della natura del XIII sec.: una biografia (Wroclaw, 1984).

10. On the dating of the Communia naturalium, see Easton, Bacon, p. 111; Crowley, Bacon, pp. 64-65; and Bacon, Communia naturalium, in Opera (Steele), fasc. 2, p. 13.

11. Williams, 'Bacon and His Edition of the Pseudo-Aristotelian Secretum secretorum'.

12. Roger Bacon, Compendium of the Study of Theology, ed. and trans. Thomas S. Maloney (Leiden, 1988), p. 47.

13. But ordinarily rendered (by me as well as by others) as On the Multiplication of Species.

14. De multiplicatione specierum is edited, translated, and commented upon in my Bacon's Philosophy of Nature.

15. Easton, Bacon, p. 111.

16. Easton, Bacon, p. 111.

17. De speculis comburentibus is edited and translated in my Bacon's Philosophy of Nature; on the dating of De speculis comburentibus, see p. xxxiii. On the content of De speculis comburentibus, see also Lindberg, 'A Reconsideration of Roger Bacon's Theory of Pinhole Images', Archive for History of Exact Sciences, 6 (1970), 214-23.

18. Communia naturalium, in Opera (Steele), fasc. 2, pp. 14-49; Opus maius, vol. 1, pp. 109-43; Opus tertium (Brewer), pp. 110-18; Opus tertium (Duhem), pp. 75-96; Opus tertium (Little), pp. 20-40. Extant portions of the Compendium studii theologie promise to deal with species later in the treatise, and there are at least two extant manuscripts dealing with species that claim to belong to Bacon's Compendium studii theologie; see Lindberg, Bacon's Philosophy of Nature, pp. xxix-xxxi; Bacon, Compendium of the Study of Theology, ed. and trans. Maloney, p. 51, ¶20.

19. Both are edited in Lindberg, Bacon's Philosophy of Nature. Bacon makes reference to the third version in Opus tertium (Brewer), p. 99.

20. On this revised version, see Bridges, vol. 2, pp. 1-2, n. 2.

21. See Bacon, Opus tertium (Duhem) and Opus tertium (Little).

22. A majority of the manuscript copies of De multiplicatione specierum identify Bacon as author (see Lindberg, Bacon's Philosophy of Nature, p. xxvi); a substantial fraction of the manuscript copies of the perspectiva do the same, including O, H, B, G, and K, though some of these in a later hand.

23. On the relationship between perspectiva and the modern subject of optics, see below, chap. I.1.1, n. 4.

24. Lindberg, Perspectiva, I.1.1. For similar themes, see Opus tertium (Duhem), p. 76; Opus tertium (Little), p. 20.

25. Lindberg, Perspectiva, I.1.1.

26. Lindberg, Perspectiva, I.1.1.

27. Lindberg, Perspectiva, I.1.1.

28. Lindberg, Perspectiva, III.3.1, ¶1.

29. On this and the following examples, see Lindberg, Perspectiva, III.3.2, ¶1 and 4.

30. On this and the following examples, see Lindberg, Perspectiva, III.3.2, ¶1 and 4.

31. Lindberg, Perspectiva III.3.3. Bacon makes similar points in Opus tertium (Brewer), pp. 116-17.

32. Lindberg, Perspectiva III.3.4.

33. Bacon, Opus maius, IV.1.1, vol. 1, pp. 97-98. On the utility of mathematics, see David C. Lindberg, 'On the Applicability of Mathematics to Nature: Roger Bacon and His Predecessors', British Journal for the History of Science, 15 (1982), 16-25; Lindberg, 'Science as Handmaiden: Roger Bacon and the Patristic Tradition', Isis, 78 (1987), 529-32. For similar themes, see Opus tertium (Brewer), pp. 105-6; Opus tertium (Little), p. 1.


Roger Bacon. Compendium Philosophiae, ed. John Sherren Brewer, Fr. Rogeri Bacon: Opus Tertium, Opus Minus, Compendium Philosophiae (Kessinger Publishing, LLC, 1859)

---., Compendium of the Study of Theology, ed. and trans. Thomas S. Maloney (Leiden, 1988).

---. De multiplicatione specierum, ed. and trans. with notes by David C. Lindberg, Roger Bacon's Philosophy of Nature (St. Augustine's Press, 1997).

---. De speculis comburentibus, ed. and trans. with notes by David C. Lindberg, Roger Bacon's Philosophy of Nature (St. Augustine's Press, 1997).

---. Lectures on Metaphysics , ed. Robert Steele, Opera Hactenus Inedita Rogeri Baconi: Metaphysica Fratris Bogeri (Kessinger Publishing, LLC, 1905).

---. Opus Maius, ed. with introduction and analytical table by John Henry Bridges, The Opus Majus of Roger Bacon (Adamant Media Corporation, 2000).

---. Opus Minus, ed. John Sherren Brewer, Fr. Rogeri Bacon: Opus Tertium, Opus Minus, Compendium Philosophiae (Kessinger Publishing, LLC, 1859).

---. Opus Tertium, ed. John Sherren Brewer, Fr. Rogeri Bacon: Opus Tertium, Opus Minus, Compendium Philosophiae (Kessinger Publishing, LLC, 1859).

---. Perspectiva (part 5 of the Opus maius), ed. with translation and study by David C. Lindberg (Oxford University Press, 1996).

Further Reading

Bagliani, Agostino Paravicini, 'Witelo et la science optique à la cour pontificale de Viterbe (1277)', Mélanges de l'école française de Rome (moyen-âge - temps modernes), 87 (1975), 425-53.

Burchardt, Jerzy. Witelo, filosofo della natura del XIII sec.: una biografia (Wroclaw, 1984).

Crowley, Theodore. Roger Bacon: The Problem of the Soul in His Philosophical Commentaries (Nauweelaerts: Louvain 1950).

Easton, Stewart. Roger Bacon and His Search for a Universal Science: A Reconsideration of the Life and Work of Roger Bacon in the Light of His Own Stated Purposes (Columbia Press: New York 1952.)

Hackett, Jeremiah. 'Scientia experimentalis: From Robert Grosseteste to Roger Bacon', in Robert Grosseteste: New Perspectives on His Thought and Scholarship, ed. James McEvoy (Dordrecht, 1994), pp. 66-76.

Little, A.G., ed. Roger Bacon: Essays, Contributed By Various Writers on the Occasion of the Commemoration of the Seventh Centenary of His Birth (Clarendon Press: Oxford 1952).

Lindberg, David C. 'Lines of Influence in Thirteenth-Century Optics: Bacon, Witelo, and Pecham', Speculum, 46 (1971), 72-75.

---. 'On the Applicability of Mathematics to Nature: Roger Bacon and His Predecessors', British Journal for the History of Science, 15 (1982), 16-25.

---. 'A Reconsideration of Roger Bacon's Theory of Pinhole Images', Archive for History of Exact Sciences, 6 (1970), 214-23.

---. 'Science as Handmaiden: Roger Bacon and the Patristic Tradition', Isis, 78 (1987), 529-32.

Williams, Steven J. 'Roger Bacon and His Edition of the Pseudo-Aristotelian Secretum secretorum,' Speculum, 69 (1994), 57-73.