#Galileo Galilei’s Dialogue on the Two Chief World Systems (1632).
Gingko organizer created by Professor Bethany Holmstrom (http://bethanyholmstrom.net/) in preparation for the Reacting to the Past game, Trial of Galileo: Aristotelianism, the “New Cosmology,” and the Catholic Church, 1616-33.
All citations are taken from the RTTP Gamebook by Frederick Purnell, Jr., Michael S. Pettersen, and Mark C. Carnes. Trial of Galileo: Aristotelianism, the “New Cosmology,” and the Catholic Church, 1616-33. New York: Reacting to the Past Consortium, 2013.
A full text of the translation is available via the Archimedes project [http://archimedes.mpiwg-berlin.mpg.de/cgi-bin/toc/toc.cgi?dir=galil_syste_065_en_1661;step=thumb].
Image from “Galileo’s Dialogue” on the Education page for the National Center for Atmospheric Research.
#Introduction (131-2)
Galileo directly addresses the reader in the introduction and provides his reasons for writing the Dialogue.
Image from Wikipedia Commons.
#First Day (133-149)
A review of and arguments for and against Aristotle’s physics unfolds during the First Day.
Image from the Museum Victoria, Australia site.
#Second Day (150-177)
They mostly discuss whether or not the Earth rotates on its axis on the Second Day.
Image from Wikipedia Commons.
#Third Day (178-194)
The annual revolution of the Earth about the Sun
Image from the Department of History and Philosophy of Science page on Copernicus, Cambridge University. http://www.hps.cam.ac.uk/starry/copernicus.html
#Fourth Day (195-6)
It’s a short day, apparently.
Galileo’s titles are listed - note that the list of titles suggests that he is an “expert,” but also hints as to his political connections
Published in Italian
Note also that the subtitle suggests that Galileo will not find one side or another (the Ptolemaic or Copernican) superior
Image from Famous Trials by Douglas O. Linder (2013). University of Missouri-Kansas City (UMKC) School of Law.
Wherein they repeat what we’ve already read in The Starry Messenger, and thus I won’t repeat any of that here.
(Note: this will be important for those of you talking about Renaissance/humanistic ideology.)
Salviati confesses they got a bit off-track yesterday, but doesn’t quite know how to get the conversation going again. Sagredo sums up the discussion.
Salviati proposes that the sun is at the center of the planetary revolutions, and the Moon orbits the Earth. Simplicio is not convinced, so Salviati works with him to draw a diagram illustrating the model.
Much of this section was conjecture on the part of Galileo, since they did not have the ability to observe parallax of the stars at this point.
“Lincean Professor Extraordinary of mathematics at the University of Pisa…Philosopher, and the principal mathematician to THE GRAND DUKE OF TUSCANY” (128)
Remember the push-back against Protestantism by the Catholic Church: the Council of Trent explicitly ruled that the scripture should not be in vernacular (so that the clergy alone could interpret it). Because his earlier work challenged Aristotlean (and the Church’s accepted) cosmology, one of the concerns from Phase One was whether or not The Starry Messenger should be written in the vernacular or in Latin.
The book will present the “reasons on both sides, “ which are “propounded impartially and without definition conclusion” (128)
BUT, notice that he presets counter-arguments within this supposed statement of support: “Some say that that decree was not the production of a sober scrutiny, but of an ill-informed passion; and one may hear some mutter that consultors altogether ignorant of astronomical observations ought not to clip the wings of speculative minds…” (131).
He’s quick to discard that counter-argument that “some” might make: he reminds the reader that he was there, in Rome, and spoke to the “eminent prelates of that Court” (131).
So Galileo frames the Dialogue as a defense of Catholicism against Protestantism - as a way to “defend the intellectual honor of Rome” according to the editors (131). He essentially claims that he’ll prove the Italians aren’t a bunch of backwater idiots to the Protestants in the North. Do you buy this?
He has “played the role of the Copernican” and will draw upon a “hypothesis purely mathematical” (131). Notice that he’ll level his attacks not necessarily against theories that the Earth doesn’t move, but will show Copernicanism is superior to the ill-informed Peripatetics
Galileo will show that “all experiments that can be made on Earth are insufficient means to conclude that it moves,…examine the celestial phenomena that support the Copernican hypothesis,…and propose an ingenious [answer to] the unresolved problem of [what causes] the tides…” (131-2)
So, according to Galileo, Copernicanism was not rejected by the Catholic Church due to “lack of knowledge…but…for reasons of piety, religion, the knowledge of the divine omnipotence, and a consciousness of the incapacity of man’s understanding” (132).
The fact that Galileo chose a dialogue to convey this message is crucial. It lets him get a little distance from the debate in some ways and absolves him from blame. Maybe. Or at least in theory, it should.
We have to think about the significance of the names here, too.
Salviati sets us up for a review of the “Aristotelian and Ptolemaic systems” along with the “Copernican system” (133). He’ll start with Aristotle…
Here, Salviati asks Simplicio to recall Aristotle’s arguments, and consider whether or not Aristotle would agree with his original findings after he looked through a telescope.
This is where footnote 9 (134) becomes important, because both meanings are used here when discussion “perfect.”
They first begin to discuss how wise men (like Socrates) profess to know very little, because they acknowledge that humans cannot know everything, whereas “divine wisdom…is infinitely infinite” (148).
This is another rhetorical strategy, of course: Galileo summarizes, via Sagredo, their discussion on the two world systems. However, the reader should note that Sagredo also weighs in here - he maintains that the Earth “enjoys the same perfection as the other integral bodies,” and that it moves (150). Sagredo asks that they move on to talk about whether or not the Earth moves.
Salviati does not agree that they have proven the Earth is like the other bodies, and is careful to say that he does not have any “definition conclusion.” And then we hear Galileo speaking through Salviati: “I only intend to produce for either side, those reasons and answers, arguments and solutions, which have been thought of by others, together with certain others that I have stumbled upon in my long search, always remitting the decision to the judgment of others” (150).
Sagredo shares the story of a Peripatetic who refuses to see the truth - even in the face of overwhelming evidence - because of Aristotle’s earlier writings (151).
They discuss various ways that people follow (or not) Aristotle, and Salviati says that people should continue to study and read Aristotle, but not “enslaves themselves to him, agreeing blindly to whatever he says” (153).
Salviati takes apart each of the arguments from II.4. He argues that the movement of the Earth could be “circular” and “eternal, and therefore natural” in opposition to the “violent motion” argument. He proposes two motions (rotation on the axis and revolves around the sun - more on Day 3 about this). Finally he gets around to the projectile arguments (shooting things, dropping things from towers/ships, etc.).
According to Salviati, the tower explanation is built on a fallacy (the assumption that the Earth does not move) itself, and this does not prove the Earth’s lack of movement. Salviati asks if Simplicio has tried the ship experiment - Simplicio confesses he has not. Salviati tells him that if he, and others, had conducted the experiment, they would find that the stone lands in the same place on the ship, whether it is moving or not.
Salviati uses a series of rolling ball experiments and cannon ball explanations to debunk the Aristotelian arguments, then also provides an elaborate scenario involving some of your buddies, a ship, gnats, water, and fish (sounds like a party!). He points out no matter how fast the ship moves, the things inside will move with the same motion/rate - they don’t speed up due to the ship’s motion.
In response to centrifugal tendency, he first discusses what causes this, and then has a bit more trouble including gravity in his analysis, because they didn’t totally have gravity - as a concept - locked down at this time.
Simplicio is still not convinced: Salviati says he never intended to change Simplicio’s mind, “much less do I dare presume to determine [an answer] definitively in this controversy” (176). Instead, he intended to prove that Aristotelians simply had not considered the evidence.
They’ll consider the Earth’s revolution around the Sun tomorrow.
Salviati and Sagredo discuss the stubbornness of Peripatetics. According to the duo, contemporary followers of Aristotle “establish the conclusion in their minds” and are unwilling to change it, but instead “discommodate and distort the premises and arguments” to fit their pre-set conclusions (178).
Simplicio apologizes for being late, but his gondola got stranded in the shallows until the tide came back in.
This is entirely the editors writing in this section, but they summarize the general argument: Galileo uses parallax to show that the “new stars” are very far from the moon, and thus are not part of the “changeable” terrestrial sphere (which includes the moon).
There is no real resolution here, but those of you that need to attack Galileo on the parallax front will want to scrutinize this section more closely.
Because they could not observe stellar parallax, the distance between the stars must be ENORMOUS. The Universe must then be immense.
This is another part where the religious Conservatives might take issue: there is a question of whether or not these things are made for us, and the issue of the magnitude of the Universe might uncomfortably remind some of Bruno’s beliefs.
Here, the editors summarize Galileo’s argument that the tides occur because the Earth moves. He thinks that the Sun or Moon cannot be the major factors in creating tidal movement. We know today, of course, that he was totally wrong.
Salviati apologizes if he has left anything unclear or gotten upset at any point - Simplicio says no apologies are necessary. Simplicio still doesn’t fully understand the Copernican model, but he says that the “concept seems more ingenious to me far than others I have heard” (196).
They all agree in admiring the “profound abysses of His infinite wisdom” (196). They all go to relax in a gondola together.
= I am buddies with the Medicis. I have powerful allies.
…so the Conservative faction should be already nervous, yes?
This is a very interesting dance he’s doing here - he’s trying to defend his position and protect himself from religious attacks before he’s even begun!
He’s doing a very interesting/careful thing rhetorically when discussing the Peripatetics (followers of Aristotle) and what, exactly, Copernicanism is superior to.
Do his attempts to “dance around” Copernicanism and the Church’s adoption of Aristotelian cosmology seem convincing?
But I doubt the Conservatives will see it that way!
Seriously. I mean, he didn’t pick “Simplicio” as the Peripatetic’s name for nothing.
You have to grasp what Aristotelian philosophy means by “perfect.” It does not mean flawless. It means “complete” here - this will come up later again, too.
Salviati’s counter-argument to Simplicio is that these “parts of the Earth” might want to “unite with the whole” and thus move “towards the center of the terrestrial globe” (135).
Salviati further argues that we cannot assume the “center of the Universe…is the same as the center of the Earth” (136).
This argument about circular motion in Aristotelian cosmology is crucial as well because, as the editors point out, “change can only occur where there is an interaction between things that are different” - so change cannot happen if all motion is circular (136).
Simplicio argues that the heavens are “inaugmentable, inalterable, impassible, and finally eternal,” which can be proved “by [the evidence of the] senses, tha tin all times past, according to memory or tradition, we see nothing removed, neither the whole outer Heaven nor any parts belonging to it” (136).
“Do they [Aristotelians] believe there shall come a time, when the Sun and Moon and other stars continue their existence and operations, but the Earth shall…be destroyed and annihilated?” He thinks they would say no, “therefore generation and corruption is int he superficial parts [of the Earth] and not the whole.” Sagredo pushes Simplicio to show how the Earth “differs from the celestial bodies” (137).
Does Sagredo find Salviati’s arguments convincing or not? Why?
Sagredo tells Simplicio that by his first argument on the corruptibility/alterable nature of the Heavens v. the Earth he “spread[s] the table with the same dishes,” and with the second he clears away the dishes “with much ado” (137). Basically, the logic the Simplicio uses is build upon the assumption of a difference between Earth and the celestial bodies, without any external proof.
Among several of the arguments that Simplicio makes, he suggest that we have not seen changes in the Heavens, but that we have on Earth. Salviati asks if China and America are “celestial bodies,” since Simplicio has “never beheld in them these alterations which you see here in Italy” (138).
Salviati asks Simplicio to explain how three different phenomena factor into his argument: comets, new stars, and sunspots (140-2). Each presents their arguments from each side, but Salviati has the last word.
SALV: “Does Aristotle not say that one cannot treat the things of Heaven confidently, because of their great remoteness?…And does he not likewise assert that we ought to prefer what the senses demonstrate, overall arguments, even apparently well grounded ones?” (144)
Sagredo then goes into a LONG discussion why everyone clings to Aristotle - Aristotle has been the foundation of so many areas of public life and research, that abandoning Aristotle would cause many different areas to fall apart (144-5).
The whole idea of the Earth being “imperfect” and the Heavens “perfect” comes to the fore here. Sagredo asks Simplicio if the “external parts of the celestial globes” might change, without altering their “perfection” (146).
Simplicio states that all the alterations on Earth are done for mankind, but changes on the other planets or the Moon would not aid mankind, and thus they experience no alterations.
They might all agree on this point, but then it diverges. Salviati thinks that human knowledge can include “some propositions as perfectly” and can, at times, “equal…the divine” (148). Simplicio does not like this a bit. Salviati points out that the process is different: God knows all in an instant, whereas we learn through “ratiocination” (149).
Another interesting note: Sagredo comes to this conclusion and phrases it as if it was a consensus among the group, without making it clear that Simplicio still is not on board with Copernicanism.
remember the “conclusion” issue from the title page?
They do a fair amount of Aristotle-follower bashing here.
IF the Earth moves, “the motion of anything that moves along with it must necessarily be imperceptible to its inhabitants, who also partake of that movement” (154). Since we are all on the Earth, we also must move as the Earth moves - so why would we notice it’s movement at all?
Salviati proposes that because everything moves in a particular way (i.e., diurnal motion) throughout the Earth, it seems odd that the Earth should be the only thing exempt from this motion (154).
Futhermore, he asks that the other two consider the huge size - “the immense magnitude of the starry sphere” - and wonders how such a huge thing could finish a revolution around the Earth in 24 hours.
Salviati points out that the packages and parcels on a moving ship do not themselves move or change their relationship in terms of the ship itself. If those parcels move, it’s because everything on the ship was knocked around - they do not independently move.
First point: why would the Earth, alone, not move? “Nature…has chosen to make an innumberable number of the most enormous bodies move, and that with an unconceivable velocity, to perform what might be done by the moderate rotation of the Earth alone?” (156)
Second point: all movement seems to be in relation to the Earth. So if we remove the Earth, the appearance of all movement will then seem to be no longer. Moreover, if you say that all the stars and planets move but not the Earth, you have to have a model where the stars and planets go in different directions. If you set up a model where the Earth moves, the apparent movement of stars and planets alike can both be explained (156).
First, we have a contradiction between approaches to science here. Salviati’s philosophy of science holds that a theory is “more and more probable as more and more evidence accumulates to support it,” as the game authors points out (157). Aristotle’s philosophy of science says that only that which “can be proven conclusively counts as scientific knowledge” (157). A small, but crucial, distinction in approaches to scientific knowledge…
Simplicio says that a “thousand inconveniences” would need to be addressed in the Copernican universe. Simplicio trots out the “violent motion argument,” the “two motions argument,” the “natural motions” argument, and the “vertical fall” argument (157-8). Lastly, he points out that many earlier astronomers (Ptolemy, Tycho Brahe, etc.) all supported the notion that Earth is at the center of the universe.
Salviato then presents the “terrestrial” arguments that Aristotelians use: dropping a ball from a tower, a stone from a ship, and cannon shots. These experiments are supposed to prove Aristotle’s theories: if the Earth moves, the argument goes, the ball and stone would land further from the tower or ship rather than falling straight down in a perpendicular way. Likewise, if cannons were shot to the west and to the east, the cannon ball moving west would land further away than the eastern shot - because the cannon ball moving west would gain distance when the earth moved. There are illustrations to accompany these arguments on pages 159-60.
Sagredo launches into a story to prove a point: Copernicans, he claims, know Aristotle. Backwards and forwards - they read Aristotle, and have mastered his opinions but have moved to Copernicanism because it made more sense. However, he argues, those that follow Aristotle and Ptolemy have not read/grasped Copernicus’s work.
Here, we get the “birds and clouds” argument (clouds and birds would not be able to travel as easily in both directions if the Earth moved), the “argument from the winds” (we would feel wind differently), and the “centrifugal tendency argument” (everything would spin off the ground, like a fast merry-go-round).
Sagredo says that Salviati’s rebuttals to these arguments, if true, “must…be infinitely more beautiful; and those [just reviewed] must be deformed” (162). As the editors point out, this is another “philosophy of science” where a “a beautiful theory is more likely to be true” (162).
Salviati says that he can’t explain how the Earth rotates exactly (whether it is internal or external), but that his not knowing doesn’t make it impossible for it to rotate.
Salviati says that whatever makes the Earth move is “similar to whatever makes Mars and Jupiter move, and which he believes also makes the starry sphere move” (171).
Simplicio argues that gravity makes parts of the Earth move downwards. Salviati says that even though this thing is called gravity, they do not fully understand it or how it works, so they cannot use it as an explanatory principle.
Simplicio: “In the Copernican position, the senses are greatly deluded” (172)
Salviati asks Simplicio how he knows the stone falls straight down from the tower.
Salviati explains (again, but in another way) how “motion in common is imperceptible” (173).
Chiaramonti also posits that it the wind would move at 2,529 mph, and that we would most certainly feel this. Salviati points out that we are carried along with the Earth and the air - so we do not feel it.
Again, Simplicio reiterates arguments that Copernicanism denies our sensory evidence, whereas Salviati counters that we “would not perceive it” (174). The example of the boat comes around again.
Salviati: we must use our reason, rather than appearances to assess observations (175).
“In the Ptolemaic hypothesis there are diseases, and in the Copernican their cures” (187).
Ptolemy introduced a complicated system of epicycles to explain contrary motions by planets - but all of these movements are easily explained “with one single motion of the Earth” (187).
Retrograde is explained away by the speed of motion for each planet.
For more, see footnote 9, page 134.
Remember: they haven’t figured out gravity yet!
Note at this point too that Simplicio gets a little nervous about their discussion, but Salviati assures him that “philosophy can only benefit from our disputes, for if our conceptions prove true, new discoveries will be made; if false, the first doctrine will be better confirmed” (136). This in a hard-core humanist/Renaissance argument for freedom of discussion/exchange of ideas.
Hmmm…so Simplicio is using, in part, sensory observations to support his position. How do the Conservatives who mocked the telescope and observations (i.e., sensory evidence) feel about this? Because he’s kind of contradicting your opinion here…
The fallacy in logic here is pretty important.
Simplicio replies that these things are too remote to see, and Salviati attacks him again: how can you say the alterations in American and China are too far away to see, but you will “believe other men’s reports,” but you can’t do so for the heavens or believe that they change?
The “new stars” here are actually supernovae, but they did not know that.
Note that Salviati brings Galileo (a.k.a., “our friend” - rather cheeky of Galileo, isn’t it?) into the conversation about sun spots (143).
Simplicio agrees with Salviati, which leads Salviati to conclude that “we may discourse of the Heavens and Sun with more certainty than Aristotle” (144).
Here, it is the unwillingness of people to “repair” their misunderstandings that might be based on Aristotle that Sagredo mocks - instead they go about trying to strengthen the building that is already falling apart rather than change or modify their logic.
Sagredo doesn’t seem so impartial/neutral now, does he?
Do you think he’s flirting with Bruno’s ideas on the infinitive universe here?
Think about riding in a car, as the editors suggest in the prior section as well.
Simplicio is enthusiastic about these arguments: “how exactly one truth agrees with another, and all conspire to render each other impregnable!” (160) Poor Simplicio - they’ll spend the rest of the day tearing these Aristotelian arguments apart.
Though Salviati says he’s already “abundantly answered, and shown the fallacy” of these arguments (172). They have “plainly proved that motion in common [is imperceptible]” according to Salviati, but he’ll humor Simplicio here.