Roger Bacon

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Many secrets of art and nature are thought by the unlearned to be magical.

Roger Bacon (c. 12141292?), also known as Doctor Mirabilis (Latin: "wonderful teacher"), was an English theologian, philosopher and Franciscan friar. An English philosopher who placed considerable emphasis on empiricism, he was one of the earliest European advocates of the modern scientific method. Later studies have emphasized his reliance on occult and alchemical traditions. All his theoretical writings were originally in Latin.


  • Oh how delightful is the taste of wisdom to those who are thus steeped in it from its very fount and origin. They who have not tried this cannot feel the delight of wisdom, just as a sick man cannot estimate the flavour of food. But because they are affected with this sort of mental sickness, and their intellect in this matter is as it were deaf from their very birth, so as not to appreciate the delight of harmony, on this account they grieve not at this so great loss of wisdom, though indeed without doubt it is an infinite loss.
    • Compendium Studii Theologiae (1292) c. viii. & Brewer's Bacon (1859) p. 466 as cited by George Gresley Perry, The Life and Times of Robert Grosseteste, Bishop of Lincoln (1871)
  • Prudens quaestio dimidium scientiae.
    • To ask the proper question is half of knowing.
    • Cited in: LIFE, 8 sept 1958, p. 73
      • Variant translation: Half of science is asking the right questions.
  • Argument is conclusive... but... it does not remove doubt, so that the mind may never rest in the sure knowledge of the truth, unless it finds it by the method of experiment. For if any man who never saw fire proved by satisfactory arguments that fire burns, his hearer's mind would never be satisfied, nor would he avoid the fire until he put his hand in it that he might learn by experiment what argument taught.
    • Cited in: Carol A. Dingle (2000) Memorable Quotations: Philosophers of Western Civilization. p. 21
  • There are in fact four very significant stumbling blocks in the way of grasping the truth, which hinder every man however learned, and scarcely allow anyone to win a clear title to wisdom, namely, the example of weak and unworthy authority, longstanding custom, the feeling of the ignorant crowd, and the hiding of our own ignorance while making a display of our apparent knowledge.
    • Cited in: John H. Woodburn, Ellsworth Scott Obourn (1965) Teaching the pursuit of science. p. 70
  • Many secrets of art and nature are thought by the unlearned to be magical.
    • Cited by Peter Nicholls (1979) The Encyclopedia of science fiction: an illustrated A to Z. p. 376

Opus Majus, c. 1267[edit]

Opus maius, 1750
  • For the things of this world cannot be made known without a knowledge of mathematics. For this is an assured fact in regard to celestial things, since two important sciences of mathematics treat of them, namely theoretical astrology and practical astrology. The first … gives us definite information as to the number of the heavens and of the stars, whose size can be comprehended by means of instruments, and the shapes of all and their magnitudes and distances from the earth, and the thicknesses and number, and greatness and smallness, … It likewise treats of the size and shape of the habitable earth … All this information is secured by means of instruments suitable for these purposes, and by tables and by canons .. For everything works through innate forces shown by lines, angles and figures.
    • Cited in: Opus majus: A translation by Robert Belle Burke. Vol 1 (1962). p. 128
  • Reasoning draws a conclusion and makes us grant the conclusion, but does not make the conclusion certain, nor does it remove doubt so that the mind may rest on the intuition of truth, unless the mind discovers it by the path of experience.
    • In: Robert Belle Burke (2002) The Opus Majus of Roger Bacon Part 2. p. 583
  • If in other sciences we should arrive at certainty without doubt and truth without error, it behooves us to place the foundations of knowledge in mathematics...
    • Bk. 1, ch. 4. Translated by Robert B. Burke, in: Edward Grant (1974) Source Book in Medieval Science. Harvard University Press. p. 93
Diagram of the eye
from Opus Majus    
  • I shall draw... a figure (which all these matters are made clear as far as possible on a surface, but the full demonstration would require a body like the eye... The eye of a cow, pig, and other animals can be used for illustration, if anyone wishes to experiment.
    • v. i. iii. 3, ed. Bridges as quoted in A.C. Crombie, Robert Grossetest and the Origins of Experimental Science 1100-1700 (1953)
  • Everything in nature completes its action through its own force and species alone... as, for example, fire by its own force dries and consumes and does many things. Therefore vision must perform the act of seeing by its own force. But the act of seeing is the perception of a visible object at a distance, and therefore vision perceives what is visible by its own force multiplied to the object. Moreover, the species of the things of world are not fitted by nature to effect the complete act of vision at once, because of its nobleness. Hence these must be aided by the species of the eye, which travels in the locality of the visual pyramid, and changes the medium and ennobles it, and renders it analogous to vision, and so prepares the passage of the species itself of the visible object... Concerning the multiplication of this species, moreover, we are to understand that it lies in the same place as the species of the thing seen, between the sight and the thing seen, and takes place along the pyramid whose vertex is in the eye and base in the thing seen. And as the species of an object in the same medium travels in a straight path and is refracted in different ways when it meets a medium of another transparency, and is reflected when it meets the obstacles of a dense body; so is it also true of the species of vision that it travels altogether along the path of the species itself of the visible object.
    • Bacon, like Grosseteste, asserts that both the active extramitted species of vision from the eye, and the intramitted species of light from object seen, were necessary for sight.
    • v. i. vii. 4, ed. Briggs as quoted in A.C. Crombie, Robert Grossetest and the Origins of Experimental Science 1100-1700 (1953)
  • Mathematics is the gate and key of the sciences... Neglect of mathematics works injury to all knowledge, since he who is ignorant of it cannot know the other sciences or the things of this world. And what is worse, men who are thus Ignorant are unable to perceive their own ignorance and so do not seek a remedy.
    • cited in: Morris Kline (1969) Mathematics and the physical world. p. 1
  • And because this Experimental Science is wholly ignored by the general run of students, for that reason I can not convince people of its utility unless I show at the same time its excellence and its property. This science alone, then, knows how to test perfectly by experience what can be done by nature, what by the industry of art, what by imposture; what the incantations, conjurations, invocations, deprecations, sacrifices (which are magical devices) seek and dream of; and what is done in them, so that all falsity may be removed and that only the truth of art and nature be retained. This science alone teaches one to consider all the insanities of magicians, not that they may be confirmed but that they may be avoided, just as logic considers sophistical argument.
    • 6th part Experimental Science, Ch.2 Tr. Richard McKeon, Selections from Medieval Philosophers Vol.2 Roger Bacon to William of Ockham
  • I use the example of the rainbow and of the phenomena connected with it, of which sort are the circle around the sun and the stars, likewise the rod lying at the side of the sun or of a star which appears to the eye in a straight line... called the rod by Seneca, and the circle is called the corona, which often has the colors of the rainbow. But neither Aristotle nor Avicenna, in their Natural Histories, has given us knowledge of things of this sort, nor has Seneca, who composed a special book on them. But Experimental Science makes certain of them. [The experimenter] considers rowers and he finds the same colors in the falling drops dripping from the raised oars when the solar rays penetrate drops of this sort. It is the same with waters falling from the wheels of a mill; and when a man sees the drops of dew in summer of a morning lying on the grass in the meadow or the field, he will see the colors. And in the same way when it rains, if he stands in a shady place and if the rays beyond it pass through dripping moisture, then the colors will appear in the shadow nearby; and very frequently of a night colors appear around the wax candle. Moreover, if a man in summer, when he rises from sleep and while his eyes are yet only partly opened, looks suddenly toward an aperture through which a ray of the sun enters, he will see colors. And if, while seated beyond the sun, he extend his hat before his eyes, he will see colors; and in the same way if he closes his eye, the same thing happens under the shade of the eyebrow; and again, the same phenomenon occurs through a glass vessel filled with water, placed in the rays of the sun. Or similarly if any one holding water in his mouth sprinkles it vigorously into the rays and stands to the side of the rays; and if rays in the proper position pass through an oil lamp hanging in the air, so that the light falls on the surface of the oil, colors will be produced. And so in an infinite number of ways, as well natural as artificial, colors of this sort appear, as the careful experimenter is able to discover.
    • 6th part Experimental Science, Ch.2 Tr. Richard McKeon, Selections from Medieval Philosophers Vol.2 Roger Bacon to William of Ockham

Opus Tertium, c. 1267[edit]

Online version
  • I have labored much in sciences and languages, and I have up to now devoted forty years [to them] after I first learned the Alphabetum; and I was always studious. Apart from two of these forty years I was always [engaged] in study [or at a place of study], and I had many expenses just as others commonly have. Nevertheless, provided I had first composed a compendium, I am certain that within quarter or half a year I could directly teach a solicitous and confident person whatever I know of these sciences and languages. And it is known that no one worked in so many sciences and languages as I did, nor so much as I did. Indeed, when I was living in the other state of life [as a Magister], people marveled that I survived the abundance of my work. And still, I was just as involved in studies afterwards, as I had been before. But I did not work all that much, since in the pursuit of Wisdom this was not required.
  • [H]aec vocatur scientia experimentalis, quae negligit argumenta, quoniam non certificant, quantumcunque sint fortia, nisi simul adsit experientia conclusionis. Et ideo haec docet experiri conclusiones nobiles omnium scientiarum, quae in aliis scientiis aut probantur per argumenta, aut investigantur per experientias naturales et imperfectas...
    • The strongest argument proves nothing so long as the conclusions are not verified by experience. Experimental science is the queen of sciences, and the goal of all speculation.
    • OQHI, 43 as cited in: James J. Walsch (1911) "Science at the Medieval Universities" in: Popular Science, May 1911, p. 449
  • Et hæc scientia certificat omnia naturalia et artificialia in particulari et in propria disciplina, per experientiam perfectam; non per argumenta, ut scientiæ pure speculativae, nec per debiles et imperfecta experientias ut scientiae operativæ. Et ideo hæc est domina omnium scientiarum præcedentium, et finis totius speculationis.
    • And this [experimental] science verifies all natural and man-made things in particular, and in their appropriate discipline, by the experimental perfection, not by arguments of the still purely speculative sciences, nor through the weak, and imperfect experiences of practical knowledge. And therefore, this is the matron of all preceding sciences, and the final end of all speculation.
    • Ch 13 ed. J. S. Brewer Opera quadam hactenus inedita (1859) p. 46
  • One man I know, and one only, who can be praised for his achievements in this science. Of discourses and battles of words he takes no heed: he follows the works of wisdom, and in these finds rest. What others strive to see dimly and blindly, like bats in twilight, he gazes at in the full light of day, because he is a master of experiment. Through experiment he gains knowledge of natural things, medical, chemical, indeed of everything in the heavens or earth. He is ashamed that things should be known to laymen, old women, soldiers, ploughmen, of which he is ignorant. Therefore he has looked closely into the doings of those who work in metals and minerals of all kinds; he knows everything relating to the art of war, the making of weapons, and the chase; he has looked closely into agriculture, mensuration, and farming work; he has even taken note of the remedies, lot casting, and charms used by old women and by wizards and magicians, and of the deceptions and devices of conjurors, so that nothing which deserves inquiry should escape him, and that he may be able to expose the falsehoods of magicians. If philosophy is to be carried to its perfection and is to be handled with utility and certainty, his aid is indispensable. As for reward, he neither receives nor seeks it. If he frequented kings and princes, he would easily find those who would bestow on him honours and wealth. Or, if in Paris he would display the results of his researches, the whole world would follow him. But since either of these courses would hinder him from pursuing the great experiments in which he delights, he puts honour and wealth aside, knowing well that his wisdom would secure him wealth whenever he chose. For the last three years he has been working at the production of a mirror that shall produce combustion at a fixed distance; a problem which the Latins have neither solved nor attempted, though books have been written upon the subject.
  • All these foregoing sciences are, properly speaking, speculative. There is indeed in every science a practical side, as Avicenna teaches in the first book of his Art of Medicine. Nevertheless, of Moral Philosophy alone can it be said that it is in the special and autonomatic sense practical, dealing as it does with human conduct with reference to virtue and vice, beatitude and misery. All other sciences are called speculative: they are not concerned with the deeds of the present or future life affecting man's salvation or damnation. All procedures of art and of nature are directed to these moral actions, and exist on account of them. They are of no account except in that they help forward right action. Thus practical and operative sciences, as experimental alchemy and the rest, are regarded as speculative in reference to the operations with which moral or political science is concerned. This science is the mistress of every department of philosophy. It employs and controls them for the advantage of states and kingdoms. It directs the choice of men who are to study in sciences and arts for the common good. It orders all members of the state or kingdom so that none shall remain without his proper work.
    • Ch. 14 as quoted in J. H. Bridges, The 'Opus Majus' of Roger Bacon (1900) Vol.1 Preface pp.x-xi

Quotes about Roger Bacon[edit]

  • Throughout the Opus Majus there is an orderly arrangement of the subject-matter formed with a definite purpose, and leading up to a central theme, the consolidation of the Catholic faith as the supreme agency for the civilization and ennoblement of mankind. For this end a complete renovation and reorganization of man's intellectual forces was needed. After a brief exposition of the four principal impediments to wisdom—authority, habit, prejudice, and false conceit of knowledge—Bacon proceeds in his second part to explain the inseparable connexion of philosophy with the highest truths of religion. ...The first condition ...of a renovation of learning is the systematic study of at least three languages besides Latin, namely Hebrew, Greek, and Arabic. The second condition was the application of mathematical method to all objects of study, whether in the world or in the Church. [mathematics] raises the understanding to the plane at which knowledge can be distinguished from ignorance. Without it other sciences are unintelligible. It reveals to us the motions of the heavenly bodies, and the laws of the propagation of force in things terrestrial, of which the propagation of light may be taken as a type; without it we are incapable of regulating the festivals of the Church; we remain in ignorance of the influences of climate upon character; of the position of cities and of the boundaries of nations whom it is the function of the Catholic Church to bring within her pale, and to control spiritually. ...But mathematical method, though essential, is insufficient. It must be supplemented by the method of experiment. Experimental science governs all the preceding sciences ('domina est omnium scientiarum praecedentium' [she is the matron of all previous sciences]), it controls their methods; in prosecuting its own special researches it makes use of their results.
    • J. H. Bridges, The 'Opus Majus' of Roger Bacon (1900) Vol.1 Preface
  • To be able to speak the language of the schools with authority was the first condition of obtaining a hearing. But he was not slow to perceive that the men who taught this philosophy were, for the most part, wholly destitute of positive knowledge. They knew no language but Latin. Beyond the shreds of arithmetic, mensuration, and astronomy taught in the manuals of the Quadrivium, they were ignorant of mathematics. Of the possibility of applying mathematical knowledge to the facts of nature they had formed no conception whatever. Their philosophy was a tangle of barren controversies reducible, for the most part, to verbal disputes. It bore no relation to the facts of real life. It held out no hope of raising the Catholic Church to the position of intellectual domination needed for establishing her authority over the Asiatic world, from which dangers were looming of appalling magnitude.
    • J. H. Bridges, The 'Opus Majus' of Roger Bacon (1900) Vol.1 Preface
  • The mind of Roger Bacon was strangely compounded of almost prophetic gleams of the future course of science, and the best principles of the inductive philosophy, with a more than usual credulity in the superstitions of his own time. Some have deemed him overrated by the nationality of the English; but, if we may have sometimes given him credit for discoveries to which he has only borne testimony, there can be no doubt of the originality of his genius.
    • Henry Hallam, Introduction to the Literature of Europe in the Fifteenth, Sixteenth, and Seventeenth Centuries (1866) Vol. 1, Ch. II, p. 130
  • Every medieval and Renaissance court had a royal astrologer who advised the duke or prince he served. ...Men such as Roger Bacon, who even in the thirteenth century was a clear and outspoken champion of the experimental method in science, and Jerome Cardan, one of the foremost mathematicians and physicians of the sixteenth century, subscribed to astrology.
  • Roger Bacon expressed a feeling which afterwards moved many minds, when he said that if he had the power he would burn all the works of the Stagirite, since the study of them was not simply loss of time, but multiplication of ignorance. Yet in spite of this outbreak every page is studded with citations from Aristotle, of whom he everywhere speaks in the highest admiration.
  • Roger Bacon, a disciple of the Arabs, also insisted on the primary necessity of Mathematics, without which no other science can be known; yet by Mathematics it is clear that he meant something very different from what we mean, including under that head even dancing, singing, gesticulation, and performance on musical instruments.
  • Contemporary with Vitellio and Peccam was... Roger Bacon, a man of almost universal genius, and who wrote on almost every branch of science. He frequently quotes Alhazen on the subject of optics, and seems to have carefully studied his writings, as well as those of other Arabians, which were the fountains of natural knowledge in those days, and which had been introduced into Europe by means of the Moors in Spain. Notwithstanding the pains this great man took with the subject of opticks, it does not appear that, with respect to theory, he made any considerable advance upon what Alhazen had done before him.
  • Great as Bacon was, he was far from being free from the mistakes and prejudices of those who went before him. Even some of the most wild and absurd opinions of the antients have the sanction of his approbation and authority. He does not hesitate to assent to an opinion... that visual rays proceed from the eye; giving this reason for it, that every thing in nature is qualified to discharge its proper functions by its own powers, in the same manner as the sun, and other celestial bodies. He acknowledges, however, that the presence of light, as well as several other circumstances, is necessary to vision.
    • Joseph Priestley, The History and Present State of Discoveries Relating to Vision, Light, and Colours (1772)
  • In his Opus Majus he demonstrates, that if a transparent body, interposed between the eye and an object, be convex towards the eye, the object will appear magnified. This observation our author certainly had from Alhazen... this writer [Bacon] gives us figures, representing the progress of rays of light through his spherical segment, as well as endeavours to give reasons why objects are magnified... From the writings of Alhazen and these observations and experiments of Bacon together, it is not improbable that some monks gradually hit upon the construction of spectacles, to which Bacon's lesser segment, not withstanding his mistake concerning it, was a nearer approach than Alhazen's... Whoever they were that pursued the discoveries of Bacon, they probably observed, that a very small convex glass, when held at a greater distance from a book, would magnify the letters more than when it was placed close to them, in which position only Bacon seemed to have used it. In the next place, they might try whether two of these small segments of a sphere placed together, or a glass convex on both sides, would not magnify more than one of them. They would then find, that two of these glasses, one for each eye, would answer the purpose of reading better than one; and lastly they might find, that different degrees of convexity, suited different persons. It is certain that spectacles were well known in the 13th century, and not long before. ...It would certainly have been a great satisfaction to us to have been able to trace the actual steps in the progress of this most useful invention, without which most persons who have a taste for reading must have had the melancholy prospect of passing a very dull and joyless old age; and must have been deprived of the pleasure of entertaining themselves by conversing with the absent and the dead, when they were no longer capable of acting their part among the living. Telescopes and microscopes are to be numbered among the superfluities of life when compared to spectacles, which may now be ranked almost among the necessities of it; since the arts of reading and writing are almost universal.
  • Bacon expresses theological and moral truths in terms of mathematical phraseology. He compares the Trinity to an equilateral triangle, argues that the divine light of grace reaches the good in a direct perpendicular ray, the weak in a refracted ray, and the bad in a reflected ray, and compares the virtues to the rational numbers, and the passions to the irrational, etc.
  • After Bruno's death, during the first half of the seventeenth century, Descartes seemed about to take the leadership of human thought... in promoting an evolution doctrine as regards the mechanical formation of the solar system... but his constant dread of persecution, both from Catholics and Protestants, led him steadily to veil his thoughts and even to suppress them. ...Since Roger Bacon, perhaps, no great thinker had been so completely abased and thwarted by theological oppression.
  • Roger Bacon had shown how easy it is, and how vain, to survey the operations of Nature and idly refer her wondrous works to chance or accident, or to the immediate interposition of God.

See also[edit]

Philosophy of science
Concepts AnalysisAnalytic–synthetic distinctionA priori and a posterioriCausalityCommensurabilityConsilienceConstructCreative synthesisDemarcation problemEmpirical evidenceExplanatory powerFactFalsifiabilityFeminist methodIgnoramus et ignorabimusInductive reasoningIntertheoretic reductionInquiryNatureObjectivityObservationParadigmProblem of inductionScientific lawScientific methodScientific revolutionScientific theoryTestabilityTheory choiceTheory-ladennessUnderdeterminationUnity of science
Metatheory of science CoherentismConfirmation holismConstructive empiricismConstructive realismConstructivist epistemologyContextualismConventionalismDeductive-nomological modelHypothetico-deductive modelInductionismEpistemological anarchismEvolutionismFallibilismFoundationalismInstrumentalismPragmatismModel-dependent realismNaturalismPhysicalismPositivism/reductionism/determinismRationalism/empiricismReceived view/semantic view of theoriesScientific realism/anti-realismScientific essentialismScientific formalismScientific skepticismScientismStructuralismUniformitarianismVitalism
Related topics AlchemyCriticism of scienceEpistemologyFaith and rationalityHistory and philosophy of scienceHistory of scienceHistory of evolutionary thoughtLogicMetaphysicsPseudoscienceRelationship between religion and scienceRhetoric of scienceSociology of scientific knowledgeSociology of scientific ignorance
Philosophers of science PlatoAristotleStoicismEpicureans
AverroesAvicennaRoger BaconWilliam of OckhamHugh of Saint VictorDominicus GundissalinusRobert Kilwardby
Francis BaconThomas HobbesRené DescartesGalileo GalileiPierre GassendiIsaac NewtonDavid Hume
Immanuel KantFriedrich SchellingWilliam WhewellAuguste ComteJohn Stuart MillHerbert SpencerWilhelm WundtCharles Sanders PeirceWilhelm WindelbandHenri PoincaréPierre DuhemRudolf SteinerKarl Pearson
Alfred North WhiteheadBertrand RussellAlbert EinsteinOtto NeurathC. D. BroadMichael PolanyiHans ReichenbachRudolf CarnapKarl PopperCarl Gustav HempelW. V. O. QuineThomas KuhnImre LakatosPaul FeyerabendJürgen HabermasIan HackingBas van FraassenLarry LaudanDaniel Dennett

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