Galileo’s Contribution to Theology

Above: Portrait of Galileo by Justus Sustermans (1597-1681), cropped  [Copyright information at]

Many people think that the traditional Christian way of interpreting the Bible was  very narrowly literal and that it was only in modern times that some Christians abandoned that approach in the face of scientific discoveries.  After all, isn’t this the reason why Galileo was condemned in 1633?

In reality, however, theologians for many centuries before Galileo — indeed, since the early Church — had understood that many things in Scripture should be interpreted in non-literal ways and had insisted that Scripture should never be interpreted in a way that contradicts what is known by reason, including facts about the natural world.  Galileo himself was able to appeal to this traditional principle in his own defense, quoting ancient and medieval Church authorities.  And the validity of the principle was admitted by Galileo’s opponents, including the Church’s top theologian at the time, Cardinal Robert Bellarmine, the very man who issued the injunction to Galileo in 1616 that barred him from defending heliocentrism.

If all that is true, then why was Galileo condemned?  Clearly, those who condemned him must have gotten something wrong not just about scientific matters but about theology as well.  Indeed, Pope St. John Paul II in an important speech about the Galileo affair said the following:

“[T]he new science, with its methods and the freedom of research which they implied, obliged the theologians [of that time] to examine their own criteria of scriptural interpretation. Most of them did not know how to do so … . Paradoxically, Galileo, a sincere believer, showed himself to be more perceptive in this regard than the theologians who opposed him.” 1

The rise of the “new science” in the 17th century created a pivotal moment for Catholic scriptural interpretation.  The two sides in the Galileo affair agreed on certain traditional principles of interpretation but understood them differently and were applying them in a situation that presented new features.  In the short term, Galileo’s opponents prevailed, but in the long term it was Galileo’s understanding of how those principles should be understood and applied that won out in the Church.  To see how and why all this happened, one must start with the principles on which both sides agreed and their roots in the early Church.

The Bible and Science in the Early Church and Middle Ages

The specific question that led to the Galileo affair — whether heliocentric astronomy is compatible with the Bible — was new.  However, the general question of the Bible’s compatibility with science had been around since antiquity.  Early Christian commentators, for example, faced the question of how to square certain features of the Creation account in the first chapter of Genesis with the science of their own time.  An obvious case was the shape of the earth.  While Genesis 1:6-10 reflects the ancient Near Eastern belief that the earth is flat, later Greek science had shown this to be false.  Aristotle in the 4th century BC had given good arguments, based on observational evidence, that the earth is a sphere; and in the 3rd century BC Eratosthenes had calculated its circumference.  What was the Christian, who believes the Bible to be the inspired and inerrant word of God, to think?

One option was to follow the Church Father Lactantius (ca. 250 – ca. 325), who took the biblical text at face value, declaring the world to be flat and rejecting the idea of a spherical earth as one of the follies of pagan learning.  Happily, Lactantius was virtually the only early Christian thinker who adopted this position.  The other option was to follow St. Augustine of Hippo (354 – 430), who treated the biblical text in a far more subtle way.

In his On the Literal Interpretation of Genesis 2 (ca. 415) St. Augustine strongly advised Christians to exercise a “pious and serious moderation” when interpreting biblical passages with regard to the natural world.  He did so for two reasons.  First, he said, there is the danger that a Christian might make false and even absurd claims about the natural world and invoke the authority of Scripture to defend those claims, thereby putting the authority of Scripture into question and exposing the Catholic faith to the ridicule of unbelievers.3  St. Augustine knew well that Christians do more than enough of that already by our sinful behavior.

St. Augustine’s second reason was that the obscurity of many scientific matters and the inherent difficulty of the task of biblical exegesis made both scientific claims and interpretations of Scripture vulnerable to error.  Therefore, he warned Christians not to “make rash assertions, or assert as known what is not known.” However, he said, if something really has been demonstrated “to be true of physical nature, we must show [that it can be reconciled] with our Scriptures.” 5

In St. Augustine’s view, there must be a presumption in favor of the literal and obvious meaning of a Scriptural text, and therefore one should not depart from it unless reason makes such an interpretation untenable — for example, if it conflicts with demonstrable facts about the physical universe.  That is not to say that St. Augustine thought that truths about the physical universe were of equal importance to the truths of faith that pertain to our salvation — on the contrary, he deemed them far less important.  But truth is truth; and no truth, whether it is of higher or lower importance, can contradict any other truth.

For St. Augustine, another reason that interpreters of Scripture should yield to facts about the physical universe is that fundamentally Scripture is not about such things.  One of his overarching principles was that the Holy Spirit, when inspiring the human authors of Sacred Scripture, “did not intend to teach men these things (that is to say, the essential nature of the things of the visible universe), things in no way profitable unto salvation.” 6

St. Augustine’s nuanced approach gave him remarkable freedom in interpreting the Book of Genesis he was able and willing to entertain myriad interpretations of a given text as reasonable.  In many cases, St. Augustine hesitated to offer any definitive interpretation when the text concerned physical matters.  He showed an equal hesitation to definitively reject alternative readings unless they implied something contrary to the Catholic faith or were ruled out by the context as radically implausible.

For instance, regarding the separation of the waters above and below the “firmament” of the sky narrated in Genesis 1:6-10 and mentioned again in Psalm 19, St. Augustine felt free to interpret it in either highly figurative ways or more physical ways.  One figurative interpretation he considered was that “heaven” and “earth” (i.e. above and below the firmament) signify the spiritual and carnal members of the Church, respectively.  A physical interpretation he considered was that the waters above and below the firmament were those respectively in a vaporous or liquid state.  By regarding either interpretation as valid, one is relieved of the burden of having to prove too much.  Yet, as the above example illustrates, St. Augustine was willing to understand Scripture as asserting truths about the physical world when it could be safely read in that way.

St. Augustine’s method of reading the creation story was continued by St. Thomas Aquinas some 800 years later.  In his treatise on the Six Days of creation in the Summa Theologiae (Ia, qq.65-74), St. Thomas made ample use of St. Augustine’s treatise on Genesis, citing it numerous times, and like St. Augustine he showed a willingness to entertain multiple interpretations, whenever possible, by sifting through various patristic commentaries and homilies.  In addition, he made use of St. Augustine’s interpretive principle of “accommodation” or “condescension”, i.e. the idea that the human authors of the Bible actually had a correct understanding of physical phenomena but wrote about them using the common modes of speech and understanding of their respective audiences, which were based on how things appeared to the senses.  Instead of attributing mistakes to the human author of Genesis (traditionally thought to be Moses), St. Thomas said that we “should rather [consider] that Moses was speaking to ignorant people, and that out of condescension to their weakness he put before them only such things as are apparent to sense.”

St. Thomas had more of an interest in science (or “natural philosophy”, as it was then called) than St. Augustine did, no doubt because of the influence Aristotle had on his thinking, and one finds attempts in his commentaries to harmonize Scripture with Aristotelian ideas about the physical universe.  This tendency to see scientific ideas expressed, albeit in a veiled or accommodated way, in Scripture has obvious dangers, as the Galileo affair four centuries later made clear.  On the whole, however, St. Thomas’s manner of interpreting Scripture was very much in line with St. Augustine’s.

How Galileo and his opponents interpreted Scripture

The Scriptural issue in the Galileo affair was, in a way, quite simple.  Galileo was defending the heliocentric theory of Copernicus, whereas there were several passages in Scripture that seemed to imply that the earth is at rest and the sun in motion around the earth, most notably Joshua 10:12-13, Ecclesiastes 1:5, and Psalm 19:5-6.  However, it was not a foregone conclusion that the Church authorities would insist on a literal reading of those passages, and Galileo had good reasons to hope that they would not. The principles of scriptural interpretation propounded by St. Augustine and used by St. Thomas were well-known and standard among Catholic exegetes and theologians.  In fact, Cardinal Bellarmine himself had made the following statement in 1615 in a public letter to Paolo Foscarini, a Carmelite friar who was a defender of Copernican ideas:

“[i]f there were a true demonstration that … the sun does not circle the earth but the earth circles the sun, then one would have to proceed with great care in explaining the Scriptures that appear contrary, and say rather that we do not understand them than that what is demonstrated is false.” 7

On the other hand, there were several factors that would naturally make the Church authorities give great weight to a literal interpretation of those passages.  First, virtually all of the Church Fathers and subsequent commentators had interpreted them in that way.  Second, geocentrism had been the mainstream scientific view for fifteen centuries and was still defended by many leading astronomers. (Heliocentrism remained highly controversial among scientists in the time of Galileo, partly for scientific reasons. There was not really a solid scientific consensus on the issue until Newton’s theoretical breakthroughs several decades later.)  Third, the burden of proof, according to the traditional view, lay with those who would depart from the most obvious and literal interpretation of a passage.  St. Augustine had spoken of the need to interpret Scripture in accordance with what is known by reason. That is why Bellarmine made it a condition for revisiting traditional scriptural interpretations that there be a “demonstration” of the truth of heliocentrism.

Nevertheless, none of this quite explains why the Galileo affair ended as it did.  When Copernicus was developing his theory in the previous century, it attracted the favorable interest of cardinals in Rome.  Galileo himself was actually encouraged to write on the subject by Cardinal Maffeo Barberini, the very man who a few years later, as Pope Urban VIII, would have him condemned.  A significant number of Catholic clergymen and theologians were favorably disposed to Copernican ideas.

There is no single reason why things turned out as they did.  Many factors, including personalities, politics, and the uneasy temper of the times — the Thirty Years War was raging — played a role.  But also important, as Pope St. John Paul II emphasized, is that the theologians of Galileo’s time failed to rise to the occasion and “examine their own criteria of scriptural interpretation.”  There were at least three new factors in the situation that contributed to this failure.

New factors.

  1. The rules of Scripture interpretation of the Council of Trent

The Council of Trent (1545-1563), which had been called to deal with the crisis of the Protestant Reformation, had laid down a disciplinary rule for interpreting Scripture that was meant to limit the danger of radical innovations in doctrine. The rule was that in interpreting scriptural passages “on matters of faith or morals” exegetes should not depart from the consensus interpretations of the Fathers of the early Church. And, as we noted above, the Fathers had taken at face value passages of Scripture that spoke as though that the earth was motionless and the sun moved.  (That was to be expected, of course, as nearly everyone in their day thought that the sun’s motion around the earth was an obvious fact, and they had at that time no reason to suspect otherwise.)

Galileo, quite reasonably, objected that astronomical questions were not “matters of faith or morals” and that therefore the rule laid down by the Council of Trent did not apply, leaving open non-literal interpretations of the relevant passages.  This is something that later theologians have taken for granted and which in retrospect seems obvious.  But Cardinal Bellarmine did not see it that way.  He argued as follows.  It is true, Bellarmine admitted, that astronomical questions do not pertain to the substance of the faith “as to their topic.” Nevertheless, he said, they become matters of faith “as to the speaker” when Scripture makes assertions about them, for it is a matter of faith that what Scripture asserts on any topic is true. 8

Of course, Bellarmine’s argument assumes that the authors of Scripture were actually intending to make assertions about astronomy in these passages, which would only follow if the Fathers were correct in thinking that they did.  In other words, if one follows the Fathers’ understanding of these passages, then they contain astronomical assertions, which become matters of faith “as to the speaker”; and if they are matters of faith, then (by Trent’s decree) one must follow the Fathers’ understanding of these passages! Bellarmine was “reasoning in a circle.”  Of course, his position was consistent, but so was Galileo’s.

In any event, it is clear that the decree of Trent, which had really been aimed at Protestant innovations, had the unforeseen collateral effect of discouraging theologians a century later from “examining their criteria of scriptural interpretation” about the new and unrelated issues raised by natural science.

  1. A new understanding of science’s methods

It is noteworthy that Bellarmine required a “demonstration” of the truth of Copernicanism before he would entertain non-literal interpretations of the relevant passages of Scripture.  This is a reflection of a conception of scientific method that prevailed before the Scientific Revolution.  For many Aristotelians, for instance, science established its conclusions by rigorously deducing them from “first principles.” Basically, the model was the kind of reasoning one finds in Euclid.  For millennia, such “necessary demonstrations” were the gold standard of rational knowledge.

This is not, however, how the new science that was being founded by Galileo and his contemporaries — which is the science of today — works.  Scientific theories are not “proved” or facts established by rigorous deduction, but by means that involve what philosophers of science call “abduction” or “inference to the best explanation” of empirical facts.9  Even today, no one would be able to “demonstrate” the truth of heliocentrism by something resembling a mathematical proof.  Bellarmine was highly skeptical that the earth’s motion could be “demonstrated” and, given the then-prevailing notion of what constituted “demonstration,” he was right to be so.

Requiring a “true demonstration” was setting the bar impossibly high, and probably much higher than St. Augustine had in mind when he spoke of what could be known “from reason and experience” about the natural world.

  1. New ideas about the autonomy of science

When Galileo was first challenged on the grounds that his advocacy of heliocentric astronomy was incompatible with Scripture, he eloquently defended himself in a very lengthy Letter to the Grand Duchess Christina, written in 1615.  The letter was not printed until three years after Galileo’s 1633 condemnation, but it did have a significant circulation in manuscript form in Rome already in 1615.  Galileo’s letter leaned heavily on St. Augustine’s On the Literal Interpretation of Genesis, numerous passages of which he quoted.  Galileo’s arguments were brilliant and incisive, but the letter gained him few new friends among theologians and ecclesiastics.

While the Letter to the Grand Duchess Christina was basically an extended presentation of and enlargement upon the arguments of St. Augustine, Galileo did on one point go somewhat beyond him.  St. Augustine had held that literal scriptural interpretations could be trumped by truths about the natural world that were already known with certainty.  Galileo went one step further.  He wrote,

“[T]herefore I should think it would be very prudent not to allow anyone to commit — and in a way oblige — scriptural passages to have to maintain the truth of any physical conclusions whose contrary could ever be proved to us by the senses or demonstrations and necessary reasons.  Indeed, who wants to put the human mind to death? Who is going to claim that everything in the world which is observable and knowable has already been seen and discovered?”10  [emphasis added]

What Galileo sensed far better than most of his contemporaries was the enormous potential of the kind of science that was then coming to birth to discover new truths about the natural world.  If many surprising new scientific discoveries were likely to be made, then prudence required that theologians be even more tentative in drawing conclusions about the natural world from scriptural passages.  If it was bad to make scriptural claims that contradict what has already been demonstrated by reason, then it was also bad to “commit” to interpretations that contradict what might well be demonstrated by future research.  Indeed, the later history of Galileo’s own case amply shows this.

Since there was so much left to discover, natural “philosophers” (as scientists were then called) had to be allowed sufficient leeway to pursue their inquiries, without having constantly to be looking over their shoulders and worrying about what some scriptural passage might be interpreted to imply about the physical world, especially given that (as St. Augustine had said) the authors of Scripture “did not intend to teach men these things” and that some passages are obscure.  After quoting Ecclesiastes to the effect that man cannot “find out” everything about what God had created, Galileo wrote,

“So one must not, in my opinion, contradict this statement and block the way of freedom of philosophizing about [i.e. scientifically studying] things of the world and of nature, as if they had all already been discovered and disclosed with certainty.” 11

What this implied, in his view, was that “in disputes about natural phenomena one must begin not with the authority of scriptural passages, but with sense experience and necessary demonstrations.” 12 (Note, by the way, that Galileo was also still to some extent thinking in the old terms about science being a matter of “necessary demonstrations,” though he always paired that with “sense experience.”)

What Galileo was arguing for, to put it in more modern terms, was a large degree of autonomy for natural science.  This was a radical idea at that time, since truths in various domains were seen as so connected to each other that the different disciplines had to some extent to proceed in tandem.  For the older kind of science, which was regarded as a part of philosophy and proceeded in a largely philosophical manner, the idea of leaving it to its own devices, so to speak, did not seem to make much sense.  But the new science was far more technical, and depended on precise measurements, experiments, mathematical calculations, and expert knowledge.  For a theologian to want to direct scientific investigation was, said Galileo, like a political ruler, though “being neither a physician nor architect, want[ing] to direct medical treatment and the construction of buildings, resulting in serious danger to the life of the unfortunate sick and in the obvious collapse of structures.” 13 (This is a typical instance of Galileo’s humor, which could at times be quite biting.)

Galileo saw the approach he was advocating as the one that gives both Scripture and science their due.  On the one hand, Galileo was a firm believer in the inspiration and inerrancy of the Bible.  On the other, he was firmly convinced of the explanatory power of the scientific enterprise.  What Galileo did was to push St. Augustine’s insights to their logical conclusion:  if Scripture is not about matters scientific, but salvific, then one should allow the scientific endeavor be what it is, namely the best guide we have to the Book of Nature, and therefore give it the benefit of the doubt in such matters.  That, in turn, allows Scripture to be what it is, the source of saving truth and therefore to be given the benefit of the doubt when it comes to matters of faith and morals.

The End of the Affair: the Lessons Learned

Returning to St. John Paul II’s 1992 address on these matters, the pope also clearly saw the value that the crisis caused by Galileo and the new science ultimately had for the Church: “The upset caused by the Copernican system thus demanded epistemological reflection on the biblical sciences, an effort which later would produce abundant fruit in modern exegetical works and which has found sanction and a new stimulus in the Dogmatic Constitution Dei Verbum of the Second Vatican Council.” 14  One can trace the outlines of this development starting with the relaxation of censorship of Copernican books in 1758, and the Holy Office’s decision in 1822 no longer to deny the imprimatur to books that taught heliocentrism.  The Church authorities recognized that it had been all but proven.

In 1893, Pope Leo XIII’s encyclical on scriptural interpretation, Providentissimus Deus, adopted the essentials of Galileo’s Augustinian approach when it comes to the Bible and science.  According to Pope Leo, since Scripture does not intend to teach things that belong to empirical science, the texts which seem to bear on scientific matters ought to, as a rule, be interpreted either figuratively or as the human authors of the Bible speaking “in terms which were commonly used at the time, and which in many instances are in daily use at this day, even by the most eminent men of science. Ordinary speech primarily and properly describes what comes under the senses.” 15 The task of Catholic exegetes is to show that whatever the true sense of a biblical passages is it does not contradict truths of the natural order.  The exegete is not to adjudicate properly scientific claims on biblical grounds.  This the basic framework adopted later by Pope Benedict XV in Spiritus Paraclitus (1920) and by Pope Pius XII in Divino Afflante Spiritu (1943).

There has also been a progressive move to avoid attempts to harmonize science and the biblical text in such a way that the biblical author is interpreted as saying the same thing as the natural scientist.  Although St. Augustine and St. Thomas advised caution in this area, they were not wholly averse, as we have seen, to indulging in such “concordism” on a conditional basis, as with St. Thomas reading the author of Genesis 1 as an Aristotelian.  Even Galileo himself was not above such moves as when, in his 1613 Letter to Castelli,16 he offered a heliocentric reading of Joshua 10:12-13, which in effect made the author of Joshua a proto-Copernican.  The problem with this strategy has always been that any revision in the scientific picture requires a revision in the biblical interpretive picture; a constant moving of the biblical goalposts.

Rather than attempting to harmonize in this way, which is based on thinking that God’s inspiration of Scripture entails his imparting perfect knowledge to the human biblical authors, it has become equally legitimate to claim that the human authors of the Bible expressed themselves according to their own spatio-temporally conditioned and therefore limited knowledge of the cosmos and nature.  This is no necessary danger to either inspiration or inerrancy, because the scientific details are not what scriptural narratives are about nor what the revelatory message is trying to convey.

Vatican II’s Dogmatic Constitution on Divine Revelation, Dei Verbum, teaches that the Holy Spirit, in inspiring writers of the Bible,

“made use of their powers and abilities, so that with Him acting in them and through them, they, as true authors, consigned to writing everything and only those things which He wanted. Therefore, since everything asserted by the inspired authors or sacred writers must be held to be asserted by the Holy Spirit, it follows that the books of Scripture must be acknowledged as teaching solidly, faithfully and without error that truth which God wanted put into sacred writings for the sake of salvation.” 17

According to Dei Verbum, the contents of Scripture are for one purpose, a salvific purpose and no other.  One might say that its salvific purpose is its formal and defining aspect.  Furthermore, inspiration and inerrancy extend to this formal aspect alone.  This is not to say that only some parts of the Bible are inspired and others are not, but to say that in all of Scripture it was neither the intention of the Holy Spirit nor the human authors to assert anything that would be ultimately irrelevant to salvation.  As St. Augustine and his student Galileo have taught us, scientific matters are wholly irrelevant to salvation.   However, one must not forget all that is implied by the term salvation history: truths “for the sake of salvation” include accounts of what God has done in history and therefore truths of the historical order.  That we mention Pontius Pilate in the creed is instructive here.

In addition, the Pontifical Biblical Commission in its 2014 commentary on Dei Verbum, The Inspiration and Truth of Sacred Scripture,18 acknowledged the possibility that inspiration does not entail a perfect knowledge on the part of the human authors of the Bible.  In part, because of the explanatory success of the modern science, “exegetes have had to recognize that not everything in the Bible is expressed in accordance with the demands of the contemporary sciences, because the biblical writers reflect the limits of their own personal knowledge, in addition to those of their time and culture.”  This is a possibility that even Galileo never countenanced.  Rather than choose recourse to accommodation theory, the Commission envisaged the possibility that, for instance, the human author of Joshua might really have thought that the sun literally moves through the sky.  Yet, this was beside the point that the author of Joshua was trying to convey.

The undeniable success of the “new science” has pushed theologians and the Church at large not only to look at certain specific passages in a new way, but to look deep into its own tradition to see Scripture in a new way.  The irony is that this “new” way is a very ancient way as we saw by looking at St. Augustine’s interpretations of the Book of Genesis.  It is due to Galileo and the practice of modern science which he pioneered, that the Church continues to retrieve her early insights into the nature of Divine Revelation and its relation to rational reflection on the Book of Nature with ever greater consistency.


[Cory Hayes holds a Ph.D. in Systematic Theology from Duquesne University in Pittsburgh, PA.  His research and teaching interests include: Byzantine and Eastern Christian theology, Philosophy of Nature, and the relation between Catholic theology, philosophy, and empirical science.]


1.. Address of John Paul II to Participants in The Plenary Session of the Pontifical Academy of Sciences, October 31, 1992.  Sec. 5.

2.. St. Augustine, On the Literal Meaning of Genesis (De Genesi ad Litteram), trans. John Hammond Taylor, in Ancient Christian Writers: The Works of the Fathers in Translation, no. 41 (New York: Newman Press, 1982).

3..  ibid., 1, 42-43

4..  St. Augustine (In Gen. op. imperf. ix., 30), quoted in Encyclical Letter Providentissimus deus of Pope Leo XIII (Nov 18, 1893), par. 18.

5.. St. Augustine, On the Literal Meaning of Genesis (De Genesi ad Litteram), i. 21, 41.

6.. St. Augustine, On the Literal Meaning of Genesis (De Genesi ad Litteram), ii. 9, 20.

7..  Robert Cardinal Bellarmine, Letter to Foscarini, in The Essential Galileo, edited and translated by Maurice A. Finocchiaro (Indianapolis: Hackett Publishing Co. Inc., 2008] Chapter 5.1, p. 149.

8.. ibid.

9..  Routledge Encyclopedia of Philosophy, article on “Inference to the Best Explanation”:

10.. Galileo Galilei, Letter to the Grand Duchess Christina, in The Essential Galileo, edited and translated by Maurice A. Finocchiaro (Indianapolis: Hackett Publishing Co. Inc., 2008] Chapter 4.2, p. 120.

11.. ibid., p. 121.

12.. ibid., p. 116.

13.. ibid., p. 125.

14.. Address of John Paul II to Participants in The Plenary Session of the Pontifical Academy of Sciences, October 31, 1992.  Sec. 6.

15.. Encyclical Letter Providentissimus deus of Pope Leo XIII (Nov 18, 1893), par. 18.

16.. Galileo Galilei, Letter to Castelli, in The Essential Galileo, edited and translated by Maurice A. Finocchiaro (Indianapolis: Hackett Publishing Co. Inc., 2008] Section 4.1.

17.. Dogmatic Constitution on Divine Revelation, Dei Verbum, sec. 11.

18.. The Inspiration and Truth of Sacred Scripture, Pontifical Biblical Commission,


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