Galileo’s letter to Duchess Christina

As his letter shows, Galileo was shrewd, calculative and politically astute

It is a well-known fact that the church hounded Galileo for his scientific convictions to the point of an inquisition that would see him to the end of his life. What is not known as well is that Galileo—and science itself—was not fundamentally at odds with religion back then. Galileo himself, for instance, was all for the Bible (as were his contemporaries such as Descartes) but against the church’s interpretation of the book, a stance that they often considered irrational if not outright illogical.

A primary source of Galileo’s beliefs, laid out by the man himself, comes in the form of a letter he wrote in 1615 to “the Most Serene Grand Duchess Mother”, one of the most powerful women in Reneissance-era Italy, the Grand Duchess Christina of Tuscany, wife of Grand Duke Francesco I de Medici.

Galileo wrote to the Duchess not casually but specifically to clarify his views when he learnt from a friend that she did not believe in his heliocentric theory. Galileo’s work at this point followed from that of Copernicus, who had already opposed the church and been branded a heretic; so in opposing the Catholic church Galileo was neither alone nor the first. Martin Luther’s 95 theses had started a movement against the church nearly 100 years earlier. The physical distance1 and the Catholic Church’s incredible power2 meant the institution could sustain generations of opposition. In this context Galileo was among its earlier opposers.

Galileo’s other, arguably more critical, intention in writing this letter was likely to secure the support of the Medici family through its reigning lady. The Medicis not only weilded absolute money and power, and not only were they effectively ruling over Tuscany—the heart of the Renaissance—but they also held sway over the church. By the time Galileo was born three members of the Medici family had not only been part of the church but had in fact been the heads of Roman Catholicism, having weilded the title of Pope. During Galileo’s own lifetime, a fourth Medici would become Pope albeit for a brief tenure.

Attempting to swing the Medicis in his favour was a strategic move by Galileo who was prepared to do whatever it took to continue working on his scientific endeavours.

For more on this see The Galileo affair: a documentary history (ed. Maurice A. Finocchiaro). For now, let us confine our interests to Galileo’s letter itself. An english translation of the entire letter has been reproduced digitally by Fordham and relevant excerpts are reproduced below.

A pamphlet and a plea

Galileo was of course clever. His letter to the Duchess is a veiled attempt at popularising his scientific stance because the letter was dispatched as a pamphlet rather than in private, likely because there was little hope of a package from a commoner like Galileo reaching the Medici household. This was in spite of his knowing that Catholic strongholds in Italy would, by design and intent, curb his letter3. It was not published in these parts until after his inquisition was drawn to a close.

Galileo’s letter underwent several corrections and stylistic edits before its final, published form which begins with the following banger:

Some years ago, as Your Serene Highness well knows, I discovered in the heavens many things that had not been seen before our own age. The … consequences which followed from them … stirred up against me no small number of professors—as if I had placed these things in the sky with my own hands in order to upset nature and overturn the sciences.

The idolatry with which he starts this letter was no doubt an attempt to win the duchess to his favour and is a recurring motif in this writing. Equally important, just as he praises Catherine so does he remind her of his own achievements.

The achievements he selects are calculated. The “many things” he refers to having discovered “in the heavens” are Jupiter and its moons (as we now know them). This is important because he had published his discovery years ago with a dedication to none other than Catherine’s son and Galileo’s former student, Cosimo II de Medici; and the moons of Jupiter, then known as stars, he had dubbed “Medicea sidera” or the Medician stars after the four Medician brothers.

Already, Galileo is reminding Catherine that he favoured and honoured the Medici family in his work, as if to say it was now her turn to honour his name.

A Church against itself

Next he attacks the men of the church all but calling them fools:

Showing a greater fondness for their own opinions than for truth they sought to deny and disprove the new things which, if they had cared to look for themselves, their own senses would have demonstrated to them. To this end they hurled various charges and published numerous writings filled with vain arguments, and they made the grave mistake of sprinkling these with passages taken from places in the Bible which they had failed to understand properly, and which were ill-suited to their purposes.

These men would perhaps not have fallen into such error had they but paid attention to a most useful doctrine of St. Augustine’s … [“]we ought not to believe anything inadvisedly on a dubious point, lest … we conceive a prejudice against something that truth hereafter may reveal to be not contrary in any way to the sacred books of either the Old or the New Testament.“

These two passages highlight beautifully Galileo’s frustration with the opposition he was facing. He was, in effect, ready to play dirty. He was shrewd, political and strategic in using what worked in his favour. And in this case he goes straight to the people opposing him to look for sympathisers.

Through his close friend the monk Benedetto Castelli, he sought the views of revered Catholic figures who favoured his interpretation of the Bible as not necessarily opposing science. Chief among these, and one Galileo favoured more than others, was St Augustine4 whom he quotes here and in several of his other writings as an example of a truly learned religious figure who agrees with Galileo insofar as the Bible goes.

Invoking Copernicus

Throughout his attempts to fend for himself, this approach helps Galileo because his argument has never been that the Bible is wrong, just that the church has been interpreting it incorrectly. He continues this line of reasoning going on to remind Catherine (see excerpt below) that the same Catholic church, headed in the past by more able men, even accepted and supported Copernicus’s work, and all he is himself doing is ‘approving’ Copernicus’s teachings and by extension, he seems to suggest, supporting rather than opposing the Church.

In doing all this he paints a picture of himself as a man out to seek the truth, intending to oppose nobody, yet unheard (“the refutation of arguments that … they have not even listened to”), wronged and ill-treated by misguided heads of the church.

…these men have resolved to fabricate a shield for their fallacies out of the mantle of pretended religion and the authority of the Bible. These they apply with little judgement to the refutation of arguments that they do not understand and have not even listened to.

First they have endeavoured to spread the opinion that such propositions in general are contrary to the Bible and are consequently damnable and heretical … [Next] they began scattering rumours among the people that before long this doctrine would be condemned by the supreme authority5

…they seek so far as possible (at least among the common people) to make this opinion seem new and to belong to me alone. They pretend not to know that its author, or rather its restorer and confirmer, was Nicholas Copernicus; and that he was not only a Catholic, but a priest and a canon. He was in fact so esteemed by the church that when the Lateran Council … took up the correction of the church calendar, Copernicus was called to Rome … to undertake its reform…

…[Copernicus] dedicated this book On the celestial revolutions to Pope Paul III. When printed, the book was accepted by the holy Church, and it has been read and studied by everyone without the faintest hint of any objection ever being conceived against its doctrines … All this they would do merely to satisfy their personal displeasure … against another man, who has no interest in Copernicus beyond approving his teachings.

Galileo’s argument here has the clarity of the sort of scientific evidence he praised himself for publishing. It is notable that not only did he not rely upon the fascination surrounding his discoveries, he also barely spoke of the strengths and watertight nature of his science. Galileo knew his audience: despite being patrons of the arts, the Medicis understood the church and its power better than they did scientific principles. So he spoke to them in their own language.

He continues to bring up Copernicus in his letter and continues to use the church against itself in an attempt to strengthen his case before Catherine. He reaches a point where, presenting his strongest argument yet, he quotes Copernicus addressing the then Pope, as Galileo himself believes, stating that science does not oppose a ‘proper’ interpretation of the Bible.

I hope to show that I proceed with much greater piety than they do, when I argue not against condemning this book, but against condemning it in the way they suggest—that is, without under standing it, weighing it, or so much as reading it. For Copernicus never discusses matters of religion or faith … which he might have interpreted erroneously. He stands always upon physical conclusions pertaining to the celestial motions … He did not ignore the Bible, but he knew very well that if his doctrine were proved, then it could not contradict the Scriptures when they were rightly understood and thus at the end of his letter of dedication addressing the pope, [Copernicus] said:

“If there should chance to be any exegetes ignorant of mathematics who pretend to skill in that discipline, and dare to condemn and censure this hypothesis of mine upon the authority of some scriptural passage twisted to their purpose, I value them not, but disdain their unconsidered judgment … mathematics is written for mathematicians, by whom, if I am not deceived, these labours of mine will be recognised as contributing something to their domain, as also to that of the Church over which Your Holiness now reigns.”

(emphasis added)

Note Galileo’s considered reproduction of Copernicus’s sly remark at the Pope: my work is not a threat to your institution; if mathematics is correct, my results are sound and they may in fact help your Church if you are open to accepting it.

How much of this is Galileo’s sincere belief is hard to say, but going by the prevalent beliefs of his time there is little reason to doubt that Galileo was not a faithful believer in the Bible. However, as a shrewd counseller for himself, it is also not implausible that Galileo recognised that devout Catholics would rather claim that their interpretation of the Bible was wrong than concede that the Bible itself was wrong when it appeared to oppose the arts. He likely used this against them to good effect.

Knocking on the Medicis’ door

Despite his hard stance, Galileo’s tone takes on the nature of an appeal as he seeks to clarifies once again that he is not against the Church:

…[if] there is anything that may be serviceable to the holy Church in making a decision concerning the Copernican system, it may be taken and utilised as seems best to the superiors. And if not, let my book be torn and burnt, as I neither intend nor pretend to gain from it any fruit that is not pious and Catholic.

Galileo understood the power the Church wielded and went out of his way to clarify repeatedly that his work was not intended to be heretical, that his work simply followed in the footsteps of a certain Copernicus whose work the Church had already accepted, and that he was open to admitting any faults in his own work or in his interpretation of works outside his areas of expertise.

But Galileo’s humility is shortlived as he goes on to use the Medicis themselves as examples of what theologians ought not do. He does of course sugarcoat this first by putting theology on a pedestal:

Let us grant then that theology is conversant with the loftiest divine contemplation, and occupies the regal throne among sciences by dignity … lf she does not descend to the lower and humbler speculations of the subordinate sciences and has no regard for them because they are not concerned with blessedness, then her professors … [have no] … authority to decide on controversies in professions which they have neither studied nor practiced. Why, this would be as if an absolute despot, being neither a physician nor an architect but knowing himself free to command, should undertake to administer medicines and erect buildings according to his whim-at grave peril of his poor patients’ lives, and the speedy collapse of his edifices.

The Medicis are squarely the intended targets of Galileo’s last sentence in the excerpt above. They were despots but by openly using that term he pretends to be referring to someone besides them—because of course it is not you about whom I speak. And the Medicis were known to fund architecture and medicine liberally: they birthed what would come to be known as renaissance after all. So Galileo knew Catherine would understand precisely what he was saying. When you want to build a grand structure, do you lay the bricks yourself or pay dues and ask an expert to do it for you?

Yet again this is an example of Galileo speaking in a language that the Medicis would comprehend. Not astronomy, not mathematics, rather first the Church and now philanthropy.

Once again Galileo drags St Augustine into the mix, quoting him thusly:

“It is to be held as an unquestionable truth that whatever the sages of this world have demonstrated concerning physical matters is in no way contrary to our Bibles … [let us] neither become seduced by the verbiage of false philosophy nor frightened by the superstition of counterfeit religion.”
Galileo quoting St Augustine

By now, having run down all his arguments that use and address the Church as well as the Medicis, to thwart the former and appeal to the latter, Galileo at last tries to speak of his philosophy and mathematics itself. Still, he does this hesitantly as if speaking down to Catherine but verbally clarifying his reverence. This brings us to the concluding phase of Galileo’s 8,000-word letter.

Of mathematics

Galileo outlines the fundamental method in which philosophy works: those who believe something to be untrue, prove that it is in fact so. He describes this approach as one that all people involved in philosophy subscribe to, even offering a curious example.

Now if truly demonstrated physical conclusions need not be subordinated to biblical passages, but the latter must rather be shown not to interfere with the former, then before a physical proposition is condemned it must be shown to be not rigorously demonstrated—and this is to be done not by those who hold the proposition to be true, but by those who judge it to be false … And Your Highness knows what happened to the late mathematician of the University of Pisa who undertook in his old age to look into the Copernican doctrine in the hope of shaking its foundations and refuting it, since he considered it false only because he had never studied it. As it fell out, no sooner had he understood its grounds, procedures, and demonstrations than he found himself persuaded, and from an opponent he became a very staunch defender of it.

This is a simple, straightforward and ideal manner in which to explain philosophy to someone who might not understand but also, like the Medicis and unlike the Church, might not be inherently opposed to it.

The importance of reading primary source material becomes evident when we turn our focus to the latter half of the excerpt above. Galileo uses as an example an unnamed “late mathematician of the University of Pisa” who tried to disprove Copernicus but was instead turned into an ardent supporter of heliocentrism. While the digitisation of this letter offers no clue as to the person Galileo is speaking of, the original letter has on the margin a note clarifying the identity of this person as Fr Clavius.

Christopher Clavius was a professor of mathematics in Rome who was initially skeptical of heliocentrism but later came to accept it as true. He also received visits from Galileo who discussed with him his discoveries through the telescope. Clavuis supported all of Galileo’s claims except those of Jupiter’s four moons which, in all fairness, he said he could not see through his telescope. Galileo unhesitatingly uses a friend, or at least an acquaintance, as an example in this letter, placing emphasis on the importance this letter bore for him in the larger debate of the Church being misplaced in its rejection of his ideas.

There is another reason Galileo’s mentioning a Pisaian professor is interesting: chief among his academic doubters was Clavius’s colleague and current professor at Pisa, Cosimo Boscagli. It would not be farfetched to imagine that Galileo was making this sly remark as if to say that Boscagli, like Clavius before him, doubts heliocentrism now but will come to change his mind once he attempts to understand the theory.

A costly frankness

The final call Galileo makes sees him quite exhausted. By now he has tossed aside his charade (“If I may speak frankly…”) and openly calls on the men of the Church to either face him on rational grounds or let go once and for all. He implores that they do not hide behind scriptures (which he calls “a dreadful weapon”) that cannot be fought against. I find this specific example to be extremely interesting because Galileo is alluding to the idea of falsification—something one cannot possibly do with a scripture—which would not be formalised until 19596 and which would be one of the core definitions for what counts as a science.

…why do they, in the thick of the battle, betake themselves to a dreadful weapon which cannot be turned aside, and seek to vanquish the opponent by merely exhibiting it? If I may speak frankly, I believe they have themselves been vanquished, and, feeling unable to stand up against the assaults of the adversary, they seek ways of holding him off. To that end they would forbid him the use of reason, divine gift of Providence, and would abuse the just authority of holy Scripture—which, in the general opinion of theologians, can never oppose manifest experiences and necessary demonstrations when rightly understood and applied. If I am correct, it will stand them in no stead to go running to the Bible to cover up their inability to understand (let alone resolve) their opponents’ arguments, for the opinion which they fight has never been condemned by the holy Church.

In addition to the observations discussed above, two other points are of note in this excerpt: first, Galileo is again (for a third time) paraphrasing St Augustine—veiling it as the “general opinion of theologians”—and clarifying that he is not opposed to the Bible, although this time his clarification seems disingeneous; second, Galileo casually nods at divinity (“reason, divine gift of Providence”) as if to say that, deep down, he is a believer in the work of a God as much as any man of the church.

Had we not known that Galileo was a clever person, we might have glossed over these phrases thrown in to his letter. But knowing him as we now do it is highly likely that every word contained within his writing was well thought to strike just the right chords with the Duchess.

Galileo ends with two interesting remarks: one that should clarify to us that he is not against the Church as an institution, rather against select men of God who seem bent upon slandering him; and second that he does in fact recognise, and is willing to accept, the power of the Supreme Pontiff (“the proper authorities”) to condemn an idea. This is another excellent example of the power the Church still wielded in Galileo’s time. Note also how he (yet again) aligns himself with established figures like Copernicus as if to say that fighting him would be no different than fighting Copernicus, a man of God himself no less.

Therefore let these men begin to apply themselves to an examination of the arguments of Copernicus and others, leaving condemnation of the doctrine as erroneous and heretical to the proper authorities … With regard to this opinion, and others which are not directly matters of faith, certainly no one doubts that the Supreme Pontiff has always an absolute power to approve or condemn … And in brief, if it is impossible for a conclusion to be declared heretical while we remain in doubt as to its truth, then these men are wasting their time clamoring for condemnation of the motion of the earth and stability of the sun, which they have not yet demonstrated to be impossible or false.

After all his attempts at appealing to Catherine in ways that Galileo believes she can appreciate his situation, he cannot resist ending his letter with a quip about the notional supremacy of his own work. In a sense it also shows a growing denial in Galileo—as anyone who has faced troubling circumstances knows—that the Church can possible do much more than speak in hushed tones against his work.

He claims it is “impossible” for the men of the Church to condemn the heliocentric model when, after all, they have done nothing to disprove it.

An alternate view

Galileo’s belief in his ability to pursuade not only Catherine de Medici but also any priest who might read his letter shows in his underlying attempts at dragging theology into his arguments. Most mathematicians in his time kept out of the Church’s purview by treating mathematics as a purely ‘general’ endeavour, not one either favouring or opposing the Church. This was regardless of what the Church had to say on these matters.

While it is one thing to see this as Galileo’s attempts at easing himself into the debate as a devout man sympathetic to the Church’s view as much as to that of mathematics, it can also be seen as daring and reckless.

Galileo effectively broke the status quo philosophers had maintained with the Church up to that point and chose instead to draw the grandiose institution into a battle. He had the truth on his side but, in the end, the Church set the rules of war and Galileo found himself handicapped. Little did he expect that, for all his writing, the inquisition ordered by the Catholic Church would not only condemn his ideas but also suspend Copernicus’s senimal work until it too was rectified.

Arguing against irrationality has always been an uphill battle and even a genius of the order of Galileo learnt that the hard way.


  1. Martin Luther was in Germany and news travelled much more slowly in those days. 

  2. Descartes, living around the same time as Galileo, would supress his own ‘heretic’ views in his publications so as not to annoy the Church. Indeed the Church would outlive them all: Newton, who would come about half-a-century later, would in fact be a great believer in the Bible to the point of irrationality. 

  3. Not only did they stop the publication of Galileo’s letter, some even modified it to sound more heretical and sent it to local Churches. Galileo fought back by sending authenticated copies through members of the church whom he knew personally—a list that included several second-order connections high up the ladder but whose aid would be in vain eventually. 

  4. See Moss, J.D., Galileo’s letter to Christina: some rhetorical considerations. Available from JSTOR

  5. The Church had not officially taken a stance against Galileo yet. It was not something they openly wanted to do (hence the inquisition) for fear of appearing reckless in public. They instead preferred to deal their cards through officials lower in the Catholic pyramid who frequently used as a threat the inevitability of a statement from a superior official. 

  6. Karl Popper, The logic of scientific discovery

10.11.23

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