August 8, 2025

One of the most instructive historical episodes in the relationship between science and religion began with the rise of Copernicanism and unfolded through the ensuing debate that culminated in the clash between Galileo Galilei and the Catholic Church.

This article focuses—briefly—on just one facet of this controversy[1], with the goal of establishing the following basic proposition: ‘Philosophy plays a pivotal role in the dialogue between science and religion.'

This facet consists of the striking fact that when Nicolaus Copernicus finally decided—under the influence of Georg Rheticus—to publish De revolutionibus (1543), a text long completed and left dormant among his belongings, it did not provoke fierce opposition from theologians (whether Lutheran or Catholic) or philosophers. In fact, Copernicus’ heliocentric proposal was no secret, since in his Commentariolus (ca. 1514) he had already offered explicit indications that the 'appearances' of celestial motions could be resolved by setting the Earth in motion. Although there were indeed opposing voices (again, both Lutheran and Catholic), these did not translate into significant persecutions or unrest. We even know of several ecclesiastical figures who, over the years, encouraged him to bring the manuscript to print.[2]

How is it then that just a few decades later, the situation changed so radically? Why, with the turn of the century, did the new astronomy and its advocates (Galileo included) become the target of such intense criticism? I will briefly address one crucial aspect that helps explain this shift in perspective and, I hope, will serve to support our initial proposition.

The Mathematical Nature of Astronomy

Since antiquity, astronomical practice was often more closely associated with mathematics than with physics. Thus, whenever we think of Ptolemaic astronomy, for instance, we should not interpret it as an attempt to establish a cosmology, but rather as a tool for calculation. Not all authors have agreed with this interpretation (I am summarizing centuries of inquiry that involved thousands of astronomers), and in fact, even Ptolemy himself is somewhat ambiguous on the matter in his writings.[3] However, it is largely accurate to consider Greek astronomy (inherited from Egyptian and Babylonian astronomy) as 'mere' geometry. As a mathematical tool, Ptolemaic astronomy became highly efficient, which is why it was widely accepted for centuries. However, approached this way, astronomy is simply a “useful fiction,” that allows prediction. It is not an actual representation of cosmology, an actual model of reality in the heavens.[4]

In very general terms, I believe there are three factors that conveniently favored the adoption of this fictionalist approach:

• In antiquity, the practice of mathematics held a higher prestige than that of physics, so conceiving astronomy as the former was, a priori, socially and academically desirable for members of the scholarly community;
• Ptolemaic theory presents certain internal inconsistencies, such that—if unresolved—it becomes impossible for it to function as a map of the cosmos; and
• Emphasizing the fictionalist nature of astronomy renders it entirely compatible with any cosmology, including, of course, one that is in contradiction with it.

The significance of this third point is that, even if the Ptolemaic system is not entirely consistent with Aristotelian cosmology, one could still enjoy the best of both worlds without falling into contradiction. The Ptolemaic theory could be used for predicting planetary positions, while simultaneously accepting and believing that the cosmos follows a different order of planetary revolutions: the one described by Aristotle.

Of course, it would be desirable for geometry to align with cosmology, but no one (at least, to the best of our knowledge, and it must be emphasized that the surviving documentary evidence is fragmentary) had been able to develop a homocentric system[5] that allowed for accurate predictions even by the observational standards of antiquity. Apollonius, Hipparchus, and later Ptolemy had indeed developed a fruitful geometry within the empirical domain, but one that was not fully aligned with the requirements of Aristotle’s cosmos.

With the rise of Christianity, a sort of Christianization of Peripatetic cosmology occurred (with some exceptions, as the reader may suspect). Contributing to this process was the fact that some biblical verses, when read literally, appear to support characteristics inherent to the Aristotelian ordering of the universe, such as the immobility of the Earth and the movement of the Sun. Ultimately, theology aligned itself with Aristotelianism.

Thus, we could now reformulate point (3) in a way that extends an aspect of fictionalism that some might regard as virtuous: no cosmological, philosophical, and/or religious belief is incompatible with any particular astronomical theory. Of course, whether fictionalism is the correct position is independent of such conveniences.

The Cosmological Nature of Astronomy

Copernicus, with his heliocentric system, and later Tycho Brahe, with his geo-heliocentric system, could offer alternative proposals to the Ptolemaic model (it is worth noting that, including Brahe’s model, by the late 16th century, there were three geometrical models of the Universe, not just two[6]). However, if these systems challenge Aristotle and—according to the aforementioned interpretation—the Bible, they can be shielded from philosophical and/or theological objections only if the fictionalist perspective is preserved. Thus, Copernicus’ conviction that his theory was indeed a map of reality provided a significant reason (among others[7]) that discouraged him from publishing his book.

When Galileo Galilei began to proclaim his preference for the Copernican theory as a reflection of physical reality (the Earth does move, and in three distinct ways, as Copernicus describes; and the Sun is stationary, becoming, rather than the Earth, the center of many—though definitely not all[8]—celestial movements), power struggles soon begun to emerge.

Galileo’s empiricist confidence in sensorial experience was grounded on the realist position: there is a world out there that we can come to know through scientific inquiry. This is the reason that ultimately led him to suggest that where conflicts arise between the Bible (or certain interpretations of the Bible) and the study of natural phenomena, theology must submit to the discoveries of science.[9]

The aim of this article is neither to provide a critical assessment of realism or Galileo’s proposals, nor of fictionalism/anti-realism. The only point I intend to make is that unlike the freedoms afforded by a fictionalist approach (where any geometric theory is compatible with any belief about the structure of the world, and thus there can be no objection to a theory on philosophical and/or theological and/or physical grounds), the realist position enables the possibility of conflicts—conflicts that have materialized on several occasions throughout history, with the case of Galileo being the most prominent.

Remarkably, the debate between realists and anti-realists concerning scientific knowledge in general—not just astronomical knowledge—remains unresolved to this day. And many are convinced that it remains unresolved because it is, in fact, unresolvable.

Conclusion

‘Realism’ and ‘fictionalism’ (or ‘antirealism’) are philosophical categories. The discussion regarding the relationship between scientific theories, reality, and revelation is philosophical in nature. How this relationship is resolved holds great significance in the way scientists and theologians engage in dialogue or polemics, as demonstrated by the changing response to Copernicanism. Therefore, the original proposition is corroborated: philosophy is not an intruder, but rather a pivotal catalyst in the science and religion discourse.

Anyone who discusses the relationship between science and religion while denying the relevance of philosophy will, in fact, end up implementing the most dangerous of philosophies... because they will be doing philosophy without assuming the responsibility of doing so.[10]

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Bibliography:

Blanco, D. (2022) “Rheticus, Realism and Scripture. An Analytical Assessment”, Science & Christian Belief 34:94–112.

Blanco, D. (2023) “La herméutica acomodacionista de Rheticus en defensa de la nueva astronomía”, Scientia et fides 11:131–147.

Copernicus, N. (1976) On the Revolutions of the Heavenly Spheres. New York: Barnes and Noble Books.

Devitt, M. (1991) Realism and Truth. Princeton: Princeton University Press.

Duhem, P. (1992) To Save the Phenomena. Chicago: The University of Chicago Press.

Finocchiaro, M. (ed.) (2008) Galileo Galilei. The Essential Galileo. Cambridge: Hackett.

Galilei, G. (1610) Sidereus Nuncius. Venice: Baglioni.

Goddu, A. (2010) Copernicus and the Aristotelian Tradition. Education, Reading, and Philosophy in Copernicus’s Path to Heliocentrism. Leiden: Brill.

Hooykaas, R. (1984) G. J. Rheticus’ Treatise on Holy Scripture and the Motion of the Earth. Amsterdam: North-Holland.

Jardine, N. (1984) The Birth of History and Philosophy of Science. Kepler’s A Defense of Tycho Against Ursus with Essays on its Provenance and Significance. Cambridge: Cambridge University Press.

Laudan, L. (1981) “A Confutation of Convergent Realism”, Philosophy of Science 48:19–49.

Leplin, J. (ed.) (1984) Scientific Realism. Berkeley: University of California Press.

Omodeo, P. (2014) Copernicus in the Cultural Debates of the Renaissance. Leiden: Brill.

Psillos, S. (1999) Scientific Realism. How Science Tracks Truth. New York: Routledge.

[Rheticus, G.] (1540) Narratio Prima. Danzig: Per Franciscum Rhodum.

Westman, R. (2011) The Copernican Question. Los Angeles: University of California Press.

Westman, R. (ed.) (2014) The Copernican Achievement. Los Angeles: University of California Press.

Zúñiga, Diego de (1584) In Job Commentaria. Toledo: Ioannes Rodericus.

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Endnotes

[1] So much has been written on this topic that it is impossible to provide a comprehensive, contextualized scholarly treatment of the subject in a short article. Readers interested in a general overview could find these references useful: For a reconstruction of Copernicus’ thought and its context, see Goddu (2010), Omodeo (2014), Westman (2011; 2014); important primary sources relevant to this discussion include: Copernicus (1976), Finocchiaro (2008), Hooykaas (1984), Rheticus (1540), Zúñica (1584). For a discussion of realism and anti-realism as applied to this case, Kepler’s text in defense of Tycho is essential (Jardine, 1984). A useful introduction on the topic can be found in Duhem (1992). In the 1980s, this debate reemerged with renewed vigor, generating a wealth of literature. See Devitt (1991), Laudan (1981), Leplin (1984), Psillos (1999). A general presentation of Rheticus’ position on the relationship between science and religion can be found in Blanco (2022; 2023).

[2] To cite a few: from the Lutheran sphere, the aforementioned Rheticus; and from the Catholic side, Tiedemann Giese and Nicholas Schönberg.

[3] For example, in the Almagest, Ptolemy seems to follow an instrumental approach; by contrast, he is clearly realist in his later Planetary Hypotheses.

[4] This scenario is somewhat intriguing: how is it that a fictitious tool proves empirically efficient? This issue is quite prominent in the history of science, and applies to many other constructs: how can the success of false theories be explained?

[5] That is, a system governed by spheres with the same center, to which the celestial bodies are attached.

[6] Actually, there were more than three. The system of Ursus, for example, although very similar to that of Brahe, was not identical to it (see Jardine 1984).

[7] Much has been written about the advisability of adopting Copernicanism before the invention of the telescope. But even after Galileo used it to observe the stars (both fixed and wandering), there were reasons to be cautious. For instance, when considering the three systems mentioned, note that the absence of parallax (which was only detected in the nineteenth century) is an expectation for both Brahe and Ptolemy, but an anomaly for Copernicus; furthermore, Galileo's observation of distinct phases in Venus is an unexpected phenomenon for ancient astronomy, while simultaneously serving as a confirmation of predictions from both Brahe's and Copernicus’ models. Thus, given these two experiences, and the same empirical adequacy, it seems one would have had good reasons to prefer the geoheliocentric system over the geocentric or heliocentric ones.

[8] The Moon, for example, does indeed have the Earth as the center of its movement, as the tradition upheld, but the Earth itself follows an orbital trajectory around the Sun. Furthermore, in his remarkable Sidereus Nuncius (Galilei 1610), Galileo claimed to have observed, thanks to his telescope, four moons around Jupiter (among other many phenomena that were considered extraordinary by the standards of the time). However, a Ptolemaic scholar could have resolved the issue by supposing that the four bodies were also planets, but with an average velocity identical to that of Jupiter, which would explain why they appeared to always accompany it.

[9] It is important to qualify this conclusion acknowledging that Galileo was devoted to the Church and believed that the Bible cannot err. For Galileo, the problem was more with theologians and their exegesis of specific passages. He also nuanced his stance suggesting that science and religion are mostly concerned with very different topics (one with nature, the other with salvation), even if there are also some rare areas of non-empty intersection.

[10] This observation draws inspiration from a similar expression shared by Professor Aecio Caïrus with his theology students (myself among them), though the original remark was formulated with a different domain in mind.

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Daniel Blanco, PhD
Universidad Nacional del Litoral, Santa Fe, Argentina

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Suggested citation: Blanco, D. (2025, August 8). Copernicanism, realism, and the import of philosophy in the dialogue between science and religion. Geoscience Research Institute. https://www.grisda.org/copernicanism-realism