Essay vs. Dialogue Rhetorical Styles in Galileo’s Works

The Assayer by Galileo Galilei is an essay first published in Rome in 1623, which is considered an outstanding example of works on the scientific method. This work presents Galilei’s revolutionary claims about the scientific method and the qualities of things. In this essay, the scientist analyzes why mathematics is the only tool for understanding physics, nature, and the Universe. Then, the Dialogue Concerning the Two World Chief Systems is an even more profound book published in 1632 which compares the heliocentric Copernican astronomical system with the geocentric Ptolemaic one. This paper aims to compare The Assayer and the Dialogue Concerning the Two World Chief Systems by Galileo Galilei in terms of the rhetorical techniques and strategies used to persuade the reader.

The Assayer Rhetorical Analysis

In The Assayer, Galileo discusses mathematics as the primary physics tool and presents his concept of primary and secondary qualities of objects. This work is written in the essay form; Galileo Galilei addresses Don Virginio Cesarini by criticizing and refuting certain statements and positions, using various rhetorical techniques. Galilei applies the rhetorical tools of ethos, pathos, and logos. He also uses rhetorical strategies like similes, amplifications, and metaphors. Although there are no dialogues in the article, the author still conducts a discussion with an imaginary interlocutor to whom the report is addressed. Appealing to this invisible interlocutor, he seems to argue with other scientists of that time, noting deficiencies and fallacies in the traditional arguments, offering his views with examples, and then indulging in reflections and explanations.

For example, at the beginning of an essay, the author addresses Don Virginio Cesarini, which creates an atmosphere of trust and privacy between the author and the reader. Galilei states, “I have never understood, Your Excellency, why it is that every one of the studies I have published to please or to serve other people has aroused a certain perverse urge to detract, steal, or deprecate that modicum of merit which I thought I had earned, at least for intention” (Galilei, 2016). In this way, Galilei shares his feelings that not all of his ideas were openly accepted by society since they were too revolutionary for that time. It is interesting that the scientist speaks openly about his personal experiences, which testifies to his straightforwardness in pursuing and defending the truth.

It is known that Galilei had a friend in the Catholic Church who later became Pope, providing him with some protection and the opportunity to publish his scientific works (Anadale, 2017). However, it is also known that Galilei met with zealous criticism among supporters of more traditional views since his statements about the importance of the mathematical method and subsequently his ideas in the field of astronomy about the nature of the heliocentric system were revolutionary. The Catholic Church officially declared that the Earth is the center of the solar system, and this doctrine at that time could be definitive when a person was judged as a friend or enemy of the church.

In the essay, Galilei presents his original ideas about the nature of matter, the importance of the mathematical method, the properties of the moon’s surface, the properties of heat and fire, and primary and secondary qualities of things. In these parts of the article, which leave most of the text, the author expresses himself clearly and harmoniously conveys his thoughts. For example, after much speculation about the potential of the telescope, the author states that: “As to his question why the moon is not smooth, I reply that it and all the other planets are inherently dark and shine by light from the sun” (Galilei, 2016, p. 9). He adds: “Hence they must have rough surfaces, for if they were smooth as mirrors no reflection would reach us from them and they would be quite invisible to us” (Galilei, 2016, p. 9). This example shows how the author finds a way to express a complex concept using just two sentences.

Galilei maintains a targeted tone when presenting original ideas to make presentation more convincing. For example, he asserts: “It now remains for me to tell Your Excellency, as I promised, some thoughts of mine about the proposition “motion is the cause of heat,” and to show in what sense this may be true” (Galilei, 2016, p. 19). The author also uses similes to present his ideas: “I ask you whether the comet’s flame is like our flames, or whether it has a different nature. If its nature is different, experiments made with our flames are not conclusive” (Galilei, 2016, p. 26). Therefore, the author’s reflections are presented with outstanding clarity and definiteness, which is proof that the essay is a more convenient form for discussing complex concepts. In the essay, he uses various rhetorical tools such as simile and metaphors.

Interestingly, in The Assayer, the author sets out some of his most famous and innovative ideas. In particular, this essay includes a statement that philosophy does not depend on the authority of well-known authors, “as so the most important thing about the claim is who made it” (Anadale, 2017). Instead, “philosophy is written in the vast book of nature which is the universe,” and to read this book, people “need to master the language of mathematics and geometry,” as, without these tools, they could not grasp any truth from observations of the physical world (Anadale, 2017). Therefore, Galilei claims that observations and not authority is the key to the truth about nature and that mathematics is the key to finding the truth through observations.

Further, Galilei claims that all objects have primary and secondary qualities. Primary qualities are shape, size, place, motion, contact, and number, and they are inseparable and inherent in things. The secondary qualities are color, sound, smell, and taste and are perceived by the senses. Therefore, Galilei implied that these qualities are not inherent in the object, but rather things have the potential to show these qualities to the observer and only exist due to the observer’s presence, which is a rather philosophical and controversial claim.

The author chose the essay form for the consistent presentation of complex scientific concepts and innovative ideas in the context of scientific thought of the time. The essay format allowed the author to express his thoughts in detail without unnecessary distractions during discussions with opponents. The disadvantage of the essay form may be the inability to use the rhetorical element of pathos, which could decrease the reader’s interest. Nevertheless, being in good standing with the Pope of that time, Galilei received a positive review from the Roman Catholic Church’s official, Giovanni de Guevara, approving that his scientific work does not have any unorthodoxy (Anadale, 2017). This result proves that the essay is generally a good choice for presenting new scientific concepts.

The Rhetorical Analysis of the Dialogue Concerning the Two World Chief Systems

This work is written in the form of a dialogue between two scholars and an intelligent layman. The two scholars are Salviati, named after the author’s close friend and representing Galileo himself, and Simplicio, named after Simplicius of Cilicia, a sixth-century scientist who had more traditional, if not simplistic, ideas about astronomy. An intelligent layman’s name is Sagredo, after Galilei’s friend Giovanni Francesco Sagredo. Besides the form of dialogue, Galilei uses rhetorical techniques like metaphors, similes, and personofication. In general, he widely applies the rhetorical elements of ethos, pathos, and logos.

Although the dialogue form lacks the advantages of the essay form associated with simplicity and straightforwardness, and it also has its benefits. By introducing three characters, Salviati, Simplicio, and Sagredo, into the text, the author gains room to maneuver in presenting ideas with which he agrees and ideas that he seeks to refute. Galilei deliberately chose the form of dialogue, paying tribute to the traditional form of philosophical discussion, despite his claim in The Assayer that authority does not determine the truth or falsity of statements, and mathematics is the only language of science (Galilei, 2016). In general, it seems that Galilei is involved in discussion with imaginary opponents only out of politeness, paying tribute to tradition or the conventional form of the scientific articles of that time. It also feels like his main goal was to present his discoveries without provoking significant public outcry since, for non-mathematicians, Galilei’s ideas might seem unfounded.

The Dialogue Concerning the Two World Chief Systems is published in a dialogue form, but this does not simplify perception or make it more accessible. Although the discussion happens livelily when the author addresses imaginary interlocutors, the reader’s perception is hampered by the spaciousness of the reasoning and too long a journey from the introduction to the main idea. For example, discussing the possibility of the sun rotating around its axis, Galilei writes, “Calm yourself, Simplicio. What does this modem author of yours say about the new stars of 1572 and 1604, and the solar spots?” (Galilei, 2006, p. 21). He adds, “As far as the comets are concerned, I, for my part, care little whether they are generated below or above the moon, nor have I ever set much store by Tycho’s verbosity” (Galilei, 2006, p. 21). Hence, the author discusses the ideas using numerous suggestions, objections, and related thoughts. He also spends some time maintaining the dialogue which adds to the intricacy of the presentation of already controversial ideas.

Given the complexity of the topic, the form of dialogue overly complicates the reader’s perception. It is possible that Galilei was forced to soften the certainty of his position, supporting the point of rhenium of Copernicus, who introduced the concept of a heliocentric system, not to become a victim of threats from the Catholic Church, and therefore chose the form of dialogue. In other words, perhaps Galilei was forced to write the text in such a way that it was confusing enough to mislead censors into printing. Despite these complexities, Galilei’s core messages are still presented with clarity and definiteness. The text was eventually banned from publication, given that the Catholic Church held a geocentric position.

Experts share differing opinions about Galilei’s rhetorical techniques used in the texts under discussion. Selcer (2020) observes that in the Dialogue Concerning the Two World Chief Systems, Galilei’s Copernican character Salviati tries to convince Sagredo, announcing, “I act the part of Copernicus in our arguments and wear his mask” (Selcer, 2020, p.). Therefore, Galilei uses the rhetorical technique of personification when an imaginable character represents Copernic. Galilei used this rhetorical technique with a Copernican mask to highlight the most exciting and scientifically significant passages in the text. Given that the Catholic Church did not favor Copernicus, it is possible that the open defense of Copernicus’s position caused the Dialogue Concerning the Two World Chief Systems to be subsequently included in the list of prohibited literature.

Zuber (1998) analyzes how Galilei used logos in his rhetoric. In particular, the scientist examines the argumentation models that Galilei used in the text. Zuber (1998) applies Aristotle’s dialectical model to “temporarily ignore, for clarity, the concreteness of real disputes to focus on their argumentative structure” (p. 181). The scientist notes that from the logos perspective, the presence of disagreements allows the interlocutors to check each other’s statements and come to “relatively confirmed conclusions” (Zuber, 1998, p.181). Therefore, the scholar names the most important aspect of the advantage of using a dialogue form. Zuber (1998) also claims that Galilei uses negative and positive testing to refute the opponent’s position and dialectically describe the movement of the Earth. Hence, Galilei extensively uses dialectical argumentation as an integral characteristic of the form of dialogue. This approach is usually applied to present the parity between the opponents, but in the text analyzed this is not the case.

Finocchiaro (2021) discusses rhetorical techniques in the Dialogue Concerning the Two World Chief Systems. The scholar asserts, that a lively discussion between the characters in the text allows presenting different points of view. In other words, the dialogue form is used to emphasize the primary importance of multilateral discussion and enables the reader to draw conclusions. Therefore, the form of dialogue creates an advantage for the parity of points of view. However, in this text, the author has made abundant use of the rhetorical instrument of pathos, including “emotionally charged passages, where various persons, books, and ideas are criticized not dispassionately but rather with ridicule, scorn, and contempt” (Finocchiaro, 2012). The possible overuse of pathos in dialogues resulted in an overly frivolous tone and the subsequent ban on publication by the Catholic Church due to disrespect for tradition.

Thus, The Assayer and the Dialogue Concerning the Two World Chief Systems by Galileo Galilei were compared in terms of the rhetorical techniques and strategies used to persuade the reader. The use of the essay form seems more in line with the author’s goal of getting his ideas as clear as possible to the reader. Although the form of the essay reduces the use of the rhetorical element of pathos, this does not impair the quality of the reader’s perception of information. At the same time, the form of dialogue creates an excessive saturation with details and pathetic techniques. As a result, it hardly fulfills its primary goal to present opponents’ positions on an equal footing.


Anadale, C. (2017). Galileo on primary and secondary qualities. Web.

Finocchiaro, M. A. (2012). Galileo and the art of reasoning: Rhetorical foundation of logic and scientific method (Vol. 61). Springer Science & Business Media.

Galilei, G. (2016). The assayer. In The controversy on the comets of 1618 (pp. 151-336). University of Pennsylvania Press.

Galilei, G. (2006). Dialogue concerning the two chief world systems. Web.

Selcer, D. (2020). 3. The mask of Copernicus and the ark of the compass: Bruno, Galileo, and the ontology of the Page. In Thinking Allegory Otherwise (pp. 60-86). Stanford University Press.

Zuber, M. S. (1998). Dialectic, dialogue, and controversy: The case of Galileo. Science in Context, 11(2), 181-203.

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