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The Metaphor of the Book of Nature


A Selection of Quotes from the Works of  Galileo Galilei

Galileo Galilei used the metaphor of the Book of Nature according to Neo-platonic perspective employed by the naturalists of Renaissance Academies. The Italian scientist did not read the Book of Nature against Scripture, but reaffirms the autonomy and self-consistency of the natural world. The “walls” to protect the autonomy of nature are built restricting the language in which nature is written, so regulating the access to its proper domain. For the first time the readability of nature seems to lose its universality. The Fathers of the Church used to say that the Book of Nature was readable by everyone, even by the illiterate; the obstacle to its reading was the absence of contemplative spirit and humility and, for Medieval theologians, the role of human sin. Galileo now points out that the true obstacle is just the ignorance of geometry and mathematics. The key-statements of Galileo’s view of the metaphor could be summarized as follows: a) God is certainly the same Author of the Two Books (cf. Copernican letters); b) Nature is written in the language of mathematics, and its characters are triangles, circles and others geometric figures; it can be read only by those who know this language (cf. The Assayer, 1623); c) Nature is the very object of natural philosophy: therefore a matter for scientists, not for theologians (cf. Dialogue on the Two Chief World Systems, 1632); d) The books on nature written or used by the cultural establishment of his time have now been surpassed by the book of nature, that is, by experimental knowledge (cf. Letter to Fortunio Liceti, 1641); e) Instead of backing each other on their own books, as philosophers do, it is much more reliable to back on the Book of Nature itself (cf. The Assayer, 1623).

The new reading proposed by Galileo, was it really a restrictive reading, theoretically based on Platonism (although Platonic mathematics has the criteria of universality and not of hermeticism), or was it rather a mere rhetorical stratagem? The Platonic cosmos, we must not forget, is not a book: to know it, is not to words that one must go, but to ideas and memory. The very belief that the created world can be read has Christian roots and rests on the theology of the Logos-Word. If Neo-platonism is able to capture the image of the book and leads its understanding, it is because of the “rationality” that the metaphor expresses, rather than for the idea of “readability.” The reasons for the success of the metaphor, which from Galileo onwards will accompany the scientific culture up to our days, seem to lie, above all, in the fact that it conveys very well the vision of a nature that had become an autonomous and consistent “source of study,” a book open before the eyes of the observer, whose reading, like that of any other book, requires order, scrutiny and application. However, it must be noticed that mathematical language is no foreign to a dimension of universality. From Galileo onward, scientific activity is nothing but the work of those who discover “laws” (whose etymology can still be traced back to one of the meanings of léghein), those who decipher a content, and then remain, at least in principle, capable of recognizing their Author. All these aspects will be present in the use of the metaphor made by men of science throughout the XVII century and for much of the XVIII century, even if the reference to the “second” book, that of Scripture, will become increasingly implicit or even absent.

“[Commenting on the prohibition to read Copernico’s De Revolutionibus] And to prohibit the whole science would be but to censure a hundred passages of holy Scripture which teach us that the glory and greatness of Almighty God are marvelously discerned in all his works and divinely read in the open book of heaven. For let no one believe that reading the lofty concepts written in that book leads to nothing further than the mere seeing of the splendor of the sun and the stars and their rising and setting, which is as far as the eyes of brutes and of the vulgar can penetrate. Within its pages are couched mysteries so profound and concepts so sublime that the vigils, labors, and studies of hundreds upon hundreds of the most acute minds have still not pierced them, even after continual investigations for thousands of years. The eyes of an idiot perceive little by beholding the external appearance of a human body, as compared with the wonderful contrivances which a careful and practiced anatomist or philosopher discovers in that same body when he seeks out the use of all those muscles, tendons, nerves, and bones; or when examining the functions of the heart and the other principal organs, he seeks the seat of the vital faculties, notes and observes the admirable structure of the sense organs, and (without ever ceasing in his amazement and delight) contemplates the receptacles of the imagination, the memory, and the understanding. Likewise, that which presents itself to mere sight is as nothing in comparison with the high marvels that the ingenuity of learned men discovers in the heavens by long and accurate observation. And that concludes what I have to say on this matter.”


“[Commentando la proibizione del De Revolutionibus di Copernico] Il proibir tutta la scienza, che altro sarebbe che un reprovar cento luoghi delle Sacre Lettere, i quali ci insegnano come la gloria e la grandezza del sommo Iddio mirabilmente si scorge in tutte le sue fatture, e divinamente si legge nell'aperto libro del cielo? Né sia chi creda che la lettura degli altissimi concetti, che sono scritti in quelle carte, finisca nel solo veder lo splendor del Sole e delle stelle e 'l lor nascere ed ascondersi, che è il termine sin dove penetrano gli occhi dei bruti e del vulgo; ma vi son dentro misteri tantro profondi e concetti tanto sublimi, che le vigilie, le fatiche e gli studi di cento e cento acutissimi ingegni non gli hanno ancora interamente penetrati con l'investigazioni continuate per migliaia e migliaia d'anni. E credino pure gli idioti che, sì come quello che gli occhi loro comprendono nel riguardar l'aspetto esterno d'un corpo umano è piccolissima cosa in comparazione de gli ammirandi artifizi che in esso ritrova un esquisito e diligentissimo anatomista e filosofo, mentre va investigando l'uso di tanti muscoli, tendini, nervi ed ossi, esaminando gli offizi del cuore e de gli altri membri principali, ricercando le sedi delle facultà vitali, osservando le maravigliose strutture de gli strumenti de' sensi, e, senza finir mai di stupirsi e di appagarsi, contemplando i ricetti dell'immaginazione, della memoria e del discorso; così quello che 'l puro senso della vista rappresenta, è come nulla in proporzion de' l'alte meraviglie che, mercé delle lunghe ed accurate osservazioni, l'ingegno degl'intelligenti scorge nel cielo. E questo è quanto mi occorre considerare circa a questo particolare”.

Lettera alla Serenissima madama la Granduchessa Madre, Cristina di Lorena, in Opere, ed. A. Favaro (Firenze: Giunti-Barbera, 1966) , vol. V, pp. 329-330.



“The holy Bible and the phenomena of nature proceed alike from the divine Word, the former as the dictate of the Holy Ghost and the latter as the observant executrix of God's commands. It is necessary for the Bible, in order to be accommodated to the understanding of every man, to speak many things which appear to differ from the absolute truth so far as the bare meaning of the words is concerned. But Nature, on the other hand, is inexorable and immutable; she never transgresses the laws imposed upon her, or cares a whit whether her abstruse reasons and methods of operation are understandable to men. For that reason it appears that nothing physical which sense-experience sets before our eyes, or which necessary demonstrations prove to us, ought to be called in question (much less condemned) upon the testimony of biblical passages which may have some different meaning beneath their words. For the Bible is not chained in every expression to conditions as strict as those which govern all physical effects; nor is God any less excellently revealed in Nature's actions than in the sacred statements of the Bible. Perhaps this is what Tertullian meant by these words: “We conclude that God is known first through Nature, and then again, more particularly, by doctrine; by Nature in His works, and by doctrine in His revealed word [Adversus Marcionem, I, 18].”


“Procedendo di pari dal Verbo divino la Scrittura Sacra e la natura, quella come dettatura dello Spirito Santo, e questa come osservantissima essecutrice de gli ordini di Dio; ed essendo, di più, convenuto nelle Scritture, per accomodarsi all'intendimento dell'universale, dir molte cose diverse, in aspetto e quanto al nudo significato delle parole, dal vero assoluto; ma, all'incontro, essendo la natura inesorabile ed immutabile, e mai non trascendente i termini delle leggi impostegli, come quella che nulla cura che le sue recondite ragioni e modi d'operare sieno o non sieno esposti alla capacità degli uomini; pare che quello degli effetti naturali che o la sensata esperienza ci pone dinanzi a gli occhi o le necessarie dimostrazioni ci concludono, non debba in conto alcuno esser revocato in dubbio, non che condennato, per luoghi della Scrittura che avessero nelle parole diverso sembiante; poi che non ogni detto della Scrittura è legato a obblighi così severi com'ogni effetto di natura, né meno eccelentemente ci si scuopre Iddio negli effetti di natura che ne' sacri detti delle Scritture: il che volse per avventura intender Tertulliano in quelle parole: Nos definimus, Deum primo natura cognoscendum, deinde doctrina recognoscendum: natura, ex operibus; doctrina, ex prædicationibus [Tertullianus, Adversus Marcionem, I, 18]”.

Lettera alla Serenissima madama la Granduchessa Madre, Cristina di Lorena, in Opere, vol. V, pp. 316-317.


“Philosophy is written in this grand book, the universe, which stands continually open to our gaze. But the book cannot be understood unless one first learns to comprehend the language and read the letters in which it is composed. It is written in the language of mathematics, and its characters are triangles, circles and others geometric figures without which it is humanly impossible to understand a single word of it; without these, one wanders about in a dark labyrinth.”

Discoveries and Opinions of Galileo, Engl. tr. by S. Drake  (New York: Doubleday, 1957), pp. 237-238.


“La filosofia [della natura] è scritta in questo grandissimo libro che continuamente ci sta aperto dinanzi a gli occhi (io dico l’universo), ma non si può intendere se prima non s’impara a intender la lingua, e conoscere i caratteri ne’ quali è scritto. Egli è scritto in lingua matematica, e i caratteri son triangoli, cerchi, ed altre figure geometriche, senza i quali mezi [sic] è impossibile a intenderne umanamente parola; senza questi è un aggirarsi vanamente per un oscuro laberinto”.

Il Saggiatore (1623), in Opere, vol. VI, p. 232.

“The book of philosophy is that which stands perpetually open before our eyes, but because it is written in characters different from those of our alphabet it cannot be read by every body; and the characters of this book are triangles, squares, circles, spheres, cones, pyramids and other mathematical figures fittest for this sort of reading.”

Engl. tr. in A.C. Crombie, Styles of Scientific Thinking in the European Tradition (London: Duckwoth, 1994), vol. I, p. 585.

“Ma io veramente stimo il libro della filosofia, esser quello che perpetuamente ci sta aperto dinanzi agli occhi; ma perché è scritto in caratteri diversi da quelli del nostro alfabeto, non può esser da tutti letto: e sono i caratteri di tal libro triangoli, quadrati, cerchi, sfere, coni, piramidi et altre figure matematiche, attissime per tal lettura”.

Lettera a Fortunio Liceti (gennaio 1641), in Opere, XVIII, p. 295

“He who looks the higher is the more highly distinguished, and turning over the great book of nature (which is the proper object of philosophy) is the way to elevate one’s gaze. And though whatever we read in that book is the creation of the omnipotent Craftsman, and is accordingly excellently proportioned, nevertheless that part is most suitable and most worthy which makes His work and His craftsmanship most evident to our view. The constitution of the universe I believe may be set in first place among all natural things that can be known, for coming before all others in grandeur by reason of its universal content, it must also stand above them all in nobility as their rule and standard.”

Dialogue Concerning the Two Chief World Systems—Ptolemaic & Copernican, Engl. tr. by S.Drake (Berkeley and Los Angeles: University of California Press, 1967), p. 3.

“Chi mira più alto, si differenzia più altamente; e ‘l volgersi al gran libro della natura, che è ‘l proprio oggetto della filosofia, è il modo per alzar gli occhi: nel qual libro, benché tutto quel che si legge, come fattura d’Artefice onnipotente, sia perciò proporzionatissimo, quello nientedimeno è più spedito e più degno, ove maggiore al nostro vedere, apparisce l’opera e l’artifizio. La costituzione dell’universo, tra i naturali apprensibili, per mio credere, può mettersi nel primo luogo: che se quella, come universal contenente, in grandezza tutt’altri avanza, come regola e mantenimento di tutto debbe anche avanzarli di nobiltà”.

Dialogo sopra i due massimi sistemi del mondo, Dedica al Gran Duca, Opere, VII, p. 27.