Given this, and moreover it being obvious that two truths can never contradict each other, the task of wise interpreters is to strive to find the true meanings of scriptural passages agreeing with those physical conclusions of which we are already certain and sure from clear sensory experience or from necessary demonstrations. Furthermore, as I already said, though Scripture was inspired by the Holy Spirit, because of the mentioned reasons many passages admit of interpretations far removed from the literal meaning, and also we cannot assert with certainty that all interpreters speak by divine inspiration; hence, I should believe that it would be prudent not to allow anyone to oblige [284] scriptural passages to have to maintain the truth of any physical conclusions whose contrary could ever be shown to us by the senses and demonstrative and necessary reasons. Who wants to fix a limit for the human mind? Who wants to assert that everything which is knowable in the world is already known? Because of this, it would be most advisable not to add anything beyond necessity to the articles concerning salvation and the definition of the Faith, which are firm enough that there is no danger of any valid and effective doctrine ever rising against them. If this is so, what greater disorder would result from adding them upon request by persons of whom we do not know whether they speak with celestial inspiration, and of whom also we see clearly that they are completely lacking in the intelligence needed to understand, let alone to criticize, the demonstrations by means of which the most exact sciences proceed in the confirmation of some of their conclusions?
I should believe that the authority of the Holy Writ has merely the aim of persuading men of those articles and propositions which are necessary for their salvation and surpass all human reason, and so could not become credible through some other science or any other means except the mouth of the Holy Spirit itself. However, I do not think it necessary to believe that the same God who has furnished us with senses, language, and intellect would want to bypass their use and give us by other means the information we can obtain with them. This applies especially to those sciences about which one can read only very small phrases and scattered conclusions in Scripture, as is particularly the case for astronomy, of which it contains such a small portion that one does not even find in it the names of all the planets; but if the first sacred writers had been thinking of persuading the people about the arrangement and the movements of the heavenly bodies, they would not have treated of them so sparsely, which is to say almost [285] nothing in comparison to the infinity of very lofty and admirable conclusions contained in such a science.
So you see, if I am not mistaken, how disorderly is the procedure of those who in disputes about natural phenomena that do not directly involve the Faith give first place to scriptural passages, which they quite often misunderstand anyway. However, if these people really believe to have grasped the true meaning of a particular scriptural passage, and if they consequently feel sure of possessing the absolute truth on the question they intend to dispute about, then let them sincerely tell me whether they think that in a natural dispute someone who happens to maintain the truth has a great advantage over another who happens to maintain the false.5 I know they will answer yes, and that the one who supports the true side will be able to provide a thousand experiments and a thousand necessary demonstrations for his side, whereas the other person can have nothing but sophisms, paralogisms, and fallacies. But if they know they have such an advantage over their opponents as long as the discussion is limited to physical questions and only philosophical weapons are used, why is it that when they come to the meeting they immediately introduce an irresistible and terrible weapon, the mere sight of which terrifies even the most skillful and expert champion? If I must tell the truth, I believe it is they who are the most terrified, and that they are trying to find a way of not letting the opponent approach because they feel unable to resist his assaults. However, consider that, as I just said, whoever has truth on his side has a great, indeed the greatest, advantage over the opponent, and that it is impossible for two truths to contradict each other; it follows therefore that we must not fear any assaults launched against us by anyone, as long as we are allowed to speak and to be heard by competent persons who are not excessively upset by their own emotions and interests.
To confirm this I now come to examining the specific passage of Joshua, concerning which you put forth three theses for their Most Serene Highnesses. I take the third one, which you advanced as mine (as indeed it is), but I add some other consideration that I do not believe I have ever told you.
Let us then assume and concede to the opponent that the words [286] of the sacred text should be taken precisely in their literal meaning, namely, that in answer to Joshua’s prayers God made the sun stop and lengthened the day, so that as a result he achieved victory; but I request that the same rule should apply to both, so that the opponent should not pretend to tie me and to leave himself free to change or modify the meanings of the words. Given this, I say that this passage shows clearly the falsity and impossibility of the Aristotelian and Ptolemaic world system, and on the other hand agrees very well with the Copernican one.
I first ask the opponent whether he knows with how many motions the sun moves. If he knows, he must answer that it moves with two motions, namely, with the annual motion from west to east and with the diurnal motion in the opposite direction from east to west.
Then, secondly, I ask him whether these two motions, so different and almost contrary to each other, belong to the sun and are its own to an equal extent. The answer must be no, but that only one is specifically its own, namely, the annual motion, whereas the other is not but belongs to the highest heaven, I mean the Prime Mobile; the latter carries along with it the sun as well as the other planets and the stellar sphere, forcing them to make a revolution around the earth in twenty-four hours, with a motion, as I said, almost contrary to their own natural motion.
Coming to the third question, I ask him with which of these two motions the sun produces night and day, that is, whether with its own motion or else with that of the Prime Mobile. The answer must be that night and day are effects of the motion of the Prime Mobile, and that what depends on the sun’s own motion is not night and day but the various seasons and the year itself.
Now, if the day derives not from the sun’s motion but from that of the Prime Mobile, who does not see that to lengthen the day one must stop the Prime Mobile and not the sun? Indeed, is there anyone who understands these first elements of astronomy and does not know that, if God had stopped the sun’s motion, He would have cut and shortened the day instead of lengthening it? For, the sun’s motion being [287] contrary to the diurnal turning, the more the sun moves toward the east the more its progression toward the west is slowed down, whereas by its motion being diminished or annihilated the sun would set that much sooner; this phenomenon is observed in the moon, whose diurnal revolutions are slower than those of the sun inasmuch as its own motion is faster than that of the sun. It follows that it is absolutely impossible to stop the sun and lengthen the day in the system of Ptolemy and Aristotle, and therefore either the motions must not be arranged as Ptolemy says or we must modify the meaning of the words of Scripture; we would have to claim that, when it says that God stopped the sun, it meant to say that He stopped the Prime Mobile, and that it said the contrary of what it would have said if speaking to educated men in order to adapt itself to the capacity of those who are barely able to understand the rising and setting of the sun.
Add to this that it is not believable that God would stop only the sun, letting the other spheres proceed; for He would have unnecessarily altered and upset all the order, appearances, and arrangements of the other stars in relation to the sun, and would have greatly disturbed the whole system of nature. On the other hand, it is believable that He would stop the whole system of celestial spheres, which could then together return to their operations without any confusion or change after the period of intervening rest.
However, we have already agreed not to change
the meaning of the words in the text; therefore it is necessary to resort to another arrangement of the parts of the world, and to see whether the literal meaning of the words flows directly and without obstacle from its point of view. This is in fact what we see happening.
For I have discovered and conclusively demonstrated that the [288] solar globe turns on itself, completing an entire rotation in about one lunar month, in exactly the same direction as all the other heavenly revolutions; moreover, it is very probable and reasonable that, as the chief instrument and minister of nature and almost the heart of the world, the sun gives not only light (as it obviously does) but also motion to all the planets that revolve around it; hence, if in conformity with Copernicus’ position the diurnal motion is attributed to the earth, anyone can see that it suffices stopping the sun to stop the whole system, and thus to lengthen the period of the diurnal illumination without altering in any way the rest of the mutual relationships of the planets; and that is exactly how the words of the sacred text sound. Here then is the manner in which by stopping the sun one can lengthen the day on the earth, without introducing any confusion among the parts of the world and without altering the words of Scripture.
I have written much more than is appropriate in view of my slight illness. So I end by reminding you that I am at your service, and I kiss your hands and pray the Lord to give you happy holidays and all you desire.
Florence, 21 December 1613.
To Your Very Reverend Paternity.
Your Most Affectionate Servant,
Galileo Galilei.
§4.2 Letter to the Grand Duchess Christina (1615)6
[309] To the Most Serene Ladyship the Grand Duchess Dowager:7
[§4.2.1] As Your Most Serene Highness knows very well, a few years ago I discovered in the heavens many particulars which had been invisible until our time. Because of their novelty, and because of some consequences deriving from them which contradict some physical propositions commonly accepted in philosophical schools, they roused against me no small number of such professors, as if I had placed these things in heaven with my hands in order to mess up nature and the sciences. These people seemed to forget that a multitude of truths contribute to inquiry and to the growth and strength of disciplines rather than to their diminution or destruction, and at the same time they showed greater affection for their own opinions than for the true ones; thus they proceeded to deny and to try to nullify those novelties, about which the senses themselves could have rendered them certain, if they had wanted to look at those novelties carefully. To this end they produced various matters, and they published some writings full of useless discussions and sprinkled with quotations from the Holy Scripture, taken from passages which they do not properly understand and which they inappropriately adduce. This was a very serious error, and they might not have fallen into it had they paid attention to St. Augustine’s very useful advice [310] concerning how to proceed with care in reaching definite decisions about things which are obscure and difficult to understand by means of reason alone. For, speaking also about a particular physical conclusion pertaining to heavenly bodies, he writes this (On the Literal Interpretation of Genesis, book 2, at the end):8 “Now then, always practicing a pious and serious moderation, we ought not to believe anything lightly about an obscure subject, lest we reject (out of love for our error) something which later may be truly shown not to be in any way contrary to the holy books of either the Old or New Testament.”
Then it developed that the passage of time disclosed to everyone the truths I had first pointed out, and, along with the truth of the matter, the difference in attitude between those who sincerely and without envy did not accept these discoveries as true and those who added emotional agitation to disbelief. Thus, just as those who were most competent in astronomical and in physical science were convinced by my first announcement, so gradually there has been a calming down of all the others whose denials and doubts were not sustained by anything other than the unexpected novelty and the lack of opportunity to see them and to experience them with the senses. However, there are those who are rendered ill-disposed, not so much toward the things as much as toward the author, by the love of their first error and by some interest which they imagine having but which escapes me. Unable to deny them any longer, these people became silent about them; but, embittered more than before by what has mellowed and quieted the others, they divert their thinking to other fictions and try to harm me in other ways. These would not really worry me any more than I was disturbed by the other oppositions, which I always laughed off, certain of the result that the business would have; I should not worry if I did not see that the new calumnies and persecutions are not limited to matters of greater or less theoretical understanding, which are relatively unimportant, but that they go further and try to damage me with stains which I do abhor and must abhor more than death. Nor can I be satisfied that these charges be known as false only by those who know me and them; their falsity must be known to every other person. These people are aware that in my [311] astronomical and philosophical studies, on the question of the constitution of the world’s parts, I hold that the sun is located at the center of the revolutions of the heavenly orbs and does not change place, and that the earth rotates on itself and moves around it. Moreover, they hear how I confirm this view not only by refuting Ptolemy’s and Aristotle’s arguments, but also by producing many for the other side, especially some pertaining to physical effects whose causes perhaps cannot be determined in any other way, and other astronomical ones dependent on many features of the new celestial discoveries; these discoveries clearly confute the Ptolemaic system, and they agree admirably with this other position and confirm it. Now, these people are perhaps confounded by the known truth of the other propositions different from the ordinary which I hold, and so they may lack confidence to defend themselves as long as they remain in the philosophical field. Therefore, since they persist in their original self-appointed task of beating down me and my findings by every imaginable means, they have decided to try to shield the fallacies of their arguments with the cloak of simulated religiousness and with the authority of the Holy Scriptures, unintelligently using the latter for the confutation of arguments they neither understand nor have heard.
At first, they tried on their own to spread among common people the idea that such propositions are against the Holy Scriptures, and consequently damnable and heretical. Then they realized how by and large human nature is more inclined to join those ventures which result in the oppression of other people (even if unjustly) than those which result in their just improvement, and so it was not difficult for them to find someone who with unusual confidence did preach even from the pulpit that it is damnable and heretical; and this was done with little compassion and with little consideration of the injury not only to this doctrine and its followers, but also to mathematics and all mathematicians. Thus, having acquired more confidence and with the vain hope that that seed which first took root in their insincere mind would grow into a tree and rise toward the sky, they are spreading among the people the rumor that it will shortly be declared heretical by the supreme authority. They also know that such a declaration not only would uproot these two conclusions, but also would render damnable all the other astronomical and physical observations and propositions [312] which correspond and are necessarily connected with them; hence, they alleviate their task as much as they can by making it look, at least among common people, as if this opinion were new and especially mine, pretending not to know that Nicolaus Copernicus was its author, or rather its reformer and confirmer.
Now, Copernicus was not only a Catholic, but also a clergyman9 and a canon, and he was so highly regarded that he was called to Rome from the remotest parts of Germany10 when under Leo X the Lateran Council was discussing the reform of the ecclesiastical calendar; at that time this reform remained unfinished only because there was still no exact knowledge of the precise length of the year and of the lunar month. Thus he was charged by the
Bishop of Fossombrone,11 who was then supervising this undertaking, to try by repeated studies and efforts to acquire more understanding and certainty about those celestial motions; and so he undertook this study, and, by truly Herculean labor and by his admirable mind, he made so much progress in this science and acquired such an exact knowledge of the periods of celestial motions that he earned the title of supreme astronomer; then in accordance with his doctrine not only was the calendar regularized, but tables of all planetary motions were constructed. Having expounded this doctrine in six parts, he published it at the request of the Cardinal of Capua12 and of the Bishop of Kulm;13 and since he had undertaken this task and these labors on orders from the Supreme Pontiff, he dedicated his book On Heavenly Revolutions to the successor of the latter, Paul III. Once printed this book was accepted by the Holy Church, and it was read and studied all over the world, without anyone ever having had the least scruple about its doctrine. Finally, now that one is discovering how well-founded upon clear observations and necessary demonstrations this doctrine is, some persons come along who, without having even seen the book, give its author the reward of so much work by trying to have him declared a heretic; this they do only in order to satisfy their special animosity, groundlessly conceived [313] against someone else who has no greater connection with Copernicus than the endorsement of his doctrine.
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