HoP 460 - Trial and Error - Galileo and the Inquisition
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Hi, I'm Peter Adamson, and you're listening to the History of Philosophy podcast, brought to you with the support of the Philosophy Department at King's College London and the LMU in Munich, online at historyofphilosophy.net. Today's episode, Trial and Error, Galileo and the Inquisition.

They say that history is written by the victors, and that goes double for the history of science. Doctors who believed in the four humors and used cupping or leeches to drain blood. Biologists who believed in spontaneous generation. Cosmologists who believed in a pervasive substance called phlogiston. Anatoms who tried to divine personality traits based on the shape of the head.

All are routinely considered to have been backward and ignorant, holding fast to theories that had insufficient empirical support, and stubborn in the face of evidence that would have undermined those theories. The verdict is even more severe when it comes to those who actively tried to suppress ideas that turned out to be true. No example leaps to mind more readily than the Catholic Church's decision to move against Copernicanism. Copernicus himself came nowhere close to seeing his theory condemned, dying some decades too early for that.

so it was left to Galileo Galilei to become a martyr for heliocentrism. He was born in 1564, 21 years after Copernicus' death, and was a fairly old man by the time he was placed on trial by the Inquisition in 1633. A lot of time had passed between the first proposal of heliocentrism and the church's most dramatic attempt to stamp it out.

As I've mentioned in previous episodes, this was in part because Copernicus's astronomy won relatively few adherents in the decades following the publication of his pathbreaking work on the revolutions. It was not just counterintuitive – do you feel like the Earth is spinning under your feet? – but also subject to technical objections, like the lack of perceived parallax in the fixed stars.

There were also plausible rival models, like that of Tycho Brahe, and then there was the lure of a compromised position suggested already by Andreas Ossiander in the preface that he added to Copernicus' treatise. One could treat heliocentrism as a merely hypothetical construction that is compatible with astronomical observations, rather than as a claim about the actual physical structure of the universe. This is exactly what Robert Bellarmine wanted Galileo to say.

In a letter of 1615, Bellarmine wrote as follows, There is no danger in saying that, by assuming the earth moves and the sun stands still, one saves all the appearances better than by postulating eccentrics and epicycles, and that is sufficient for the mathematician.

However, it is different to want to affirm that in reality, the sun is at the center of the world and only turns on itself without moving from east to west. This is a very dangerous thing, likely not only to irritate all scholastic philosophers and theologians, but also to harm the holy faith by rendering holy scripture false. Copernicism would render holy scripture false because of the biblical passages I mentioned last time, such as the one mentioning the miracle of the sun's ceasing its motion.

If there were definitive proof that the earth goes around the sun, that would be one thing. But in the absence of such proof, it was up to the church and its tradition to determine the meaning of scripture. It's worth emphasizing that it was this, and not really the motion of the earth as such, that was really at stake for a man like Bellarmine. The church's rejection of heliocentrism must be understood within the context of the Counter-Reformation.

not because that movement was somehow anti-scientific or anti-intellectual. After all, scholastic thinkers of the Counter-Reformation were among the leading intellectuals of Europe, rather because the rise of Protestantism had made it vital to insist on the Church's unchallenged authority in the interpretation of Scripture. As so often seeing himself as a moderate, Bellarmine was nonetheless happy for Galileo and other mathematicians to consider Copernicanism as a useful hypothesis.

So, when Galileo was first investigated by the Inquisition after a complaint brought by the Dominican Niccolò Lorini in 1615, Bellarmine simply instructed him not to defend heliocentrism as a "proven physical theory". This put Galileo in an awkward situation since he was convinced that the theory was, in fact, proven.

He had at first been attracted by heliocentrism without being totally convinced. Thus he spoke favorably of the Copernican account in a letter to Kepler in 1597, but stopped short of fully committing himself. What changed his mind was the telescope. After hearing reports about the telescope, which had been invented in Holland in 1608, he built his own instrument and then worked on improving its magnifying power.

Soon he was able to see that there are moons orbiting around Jupiter, laying to rest the notion that all heavenly bodies go around the Earth. He observed sunspots, whose motion across the surface of the Sun showed that it too is probably revolving. Also visible were the phases of Venus, that is the incomplete illumination of this planet as it orbits the Sun and is lit up from different angles.

Mars could be seen to vary in apparent size as its distance from the Earth varied, again in keeping with what Copernicus' theory would predict. So, quite literally in light of all this, Galilei was saying by 1611 that there is certain demonstration that the planets go around the sun, and by 1615 that Copernicus' opinion was certain.

When he requested that Galileo be investigated, Lorini complained that the heliocentrists not only disagree with traditional readings of the Bible, but also "trapple underfoot all of Aristotle's philosophy, which is so useful to scholastic theology." Yet Galileo insisted that if Aristotle had been shown the telescopic observations, he would have been the first to adopt Copernicanism.

Following the dictates of empirical observation is a deeper commitment of Aristotelianism than any particular idea about the structure of the cosmos. Given the new empirical findings, it would be against the spirit of Aristotle's methodology to continue upholding his cosmology. And speaking of methodology, Galileo rejected out of hand the notion that Copernicus' account had been put forward only as a useful hypothesis.

He rightly pronounced Oseander's preface to be an extraneous addition, and one foreign to Copernicus' own thought. In fact, the whole point of On the Revolutions had been to establish heliocentrism as a physical reality. Thus, Galileo said that Copernicus must either be wholly condemned or left alone. Even though Galileo felt he had proof on his side, he recognized the need to respond to counter-arguments.

First, there was the familiar concern that if Copernicus were right, then things wouldn't fall straight down when dropped from a height, but would land far away as the earth rotates underneath. Yet if we let a stone fall from a tower or a ship's mast, it lands right next to the bottom. Not a problem, argued Galileo. If the earth started to move after being at rest, everything might lurch to the side. But since the earth is already rotating, a stone is already rotating along with everything else when it is dropped.

That rotation simply continues as it falls, meaning that it moves together with the tower or mast. Showing his penchant for rhetorically powerful thought experiments, Galileo asks us to imagine a ship moving quickly at sea. In its hold, butterflies are fluttering about, and there is a tank full of fish. From the perspective of someone watching them down in the hold, butterflies and fish would seem to move just as they do when the boat is standing still in port, even though they are in fact being carried along with the boat.

It's worth emphasizing here that these really are thought experiments, not real ones. Though Galileo did depend on empirical observation when he used the telescope, in this case, he thought that one could simply reflect and see that the motion of the earth would not cause lateral movement of the things on the earth. When it came to the objection that some scriptural passages implied geocentrism, Galileo was dismissive.

He discusses the issue in various writings from around 1615, including a letter addressed to the Grand Duchess Christina, a member of the Medici clan. While he of course admits that scripture is always true, it is often difficult to interpret. A tactically astute premise given that Catholic theologians like Bellarmine were insisting against Protestant rivals that the Bible does require expert exegesis.

Since the Bible is aimed at a common readership and concerns itself primarily with spiritual and moral matters, we can hardly expect that it would use precise language when it comes to recondite matters of astronomy. On such matters, mathematics and physics tell us what is true, and we must understand scripture in the light of these dictates. Galileo is scathing about theologians who reach for the irresistible and terrible weapon of condemnation when they find that they have no good arguments on their side.

They should just keep their noses out of the business of astronomy, a field in which they have no special expertise. They don't even realize that to ban Copernicanism would mean banning astronomy as a whole. Since with the advent of the telescope, anyone who knows what they are doing will have to accept heliocentrism. Galileo was not alone in this fight. Tommaso Campanella wrote a defense of his fellow Italian in 1622, which suggested that if anything, Galileo's manner of philosophizing was more compatible with scripture than Aristotelianism.

But in any case, Galileo should be excused, given that he had never argued from a theological point of view. Here, Campanella echoes the strategy used by Camilla Erculani's lawyer, who may recall that he used almost the same phrase to defend her physical inquiries into the causes of Noah's flood. Campanella also predicted that, in the long run, it would bring the church into disgrace to suppress scientific inquiry.

This concern does seem to have carried some weight with the church authorities. When Galileo was brought to trial in 1633, the inquisitors at first tried to work out a kind of plea bargain, showing lenience towards an aged and celebrated mathematician who would help to maintain the reputation of their own tribunal.

Besides, during the initial hearings, Galileo triumphantly produced a written record of his exchange with Bellarmine from almost twenty years earlier, when he had simply been warned to teach heliocentrism as a fruitful hypothesis and not an established fact. This, he said, is exactly what he'd been doing ever since. He had never, to his recollection, been told not to discuss the topic in any way whatsoever. Unfortunately for all concerned, other figures in the Holy Office undermined the plea bargain.

In a modern study of the trial, this has been called a miscarriage of justice. The church didn't just condemn Galileo for upholding the truth, it violated its own legal procedures to do so. What moved them to employ such underhanded techniques against Galileo? Well, Galileo had in fact been incautious and provocative.

Feeling relatively secure after being let off without warning from Bellarmine, he published his famous "Dialogue on the Two Chief World Systems" in 1632, a text that makes his sympathy for Copernicanism all too evident. The sitting Pope, Urban VIII, had been an admirer of Galileo, but turned against him, perhaps in part because he found it useful to have an ideological scapegoat in unsettled political times.

It surely didn't help that Galileo allowed the plodding Aristotelian spokesman of his dialogue, who bears the belittling name Simplicio, to repeat an argument the Pope himself had raised. Urban had pointed out to Galileo that an omnipotent god could surely create either a heliocentric or geocentric universe, so that one should simply keep an open mind. We must not, he reportedly told Galileo, bind divine power and wisdom.

Unlike God, Galileo had shown rather limited wisdom by putting the Pope's argument into the mouth of Simplicio, whose very name indicates that he is a simpleton. He perhaps thought he was covered by what he said about this character in the preface to the dialogue. The Aristotelian spokesman is in fact named after the late ancient commentator Simplicius. But presumably neither Pope Urban nor anyone else was buying that, any more than they believed Galileo's claim that his dialogue treats Copernicanism only as a hypothesis.

In fact, the work makes a sustained case for heliocentrism, and is not shy about emphasizing how convincing that case is. From the modern-day vantage point, though, the problematic thing about the dialogue is, of course, not its overall conclusion, but what Galileo called the "principle argument" for that conclusion. This argument is based on the rise and fall of the tides, the topic to which Galileo had also dedicated a separate treatise.

His idea is that the tides are caused by the double motion of the Earth, as it spins on its axis and orbits the Sun. He explains how this is meant to work with another thought experiment, asking us to imagine a moving tank full of water, and explaining that the water will oscillate along with the motion of the tank.

Of course, Galileo was wrong about this, and wrong in part because of the very point he had made with reference to stones falling from ships' masts and towers: the water of the oceans is simply carried along with the rest of the Earth, so its astronomical motion cannot be the cause of tidal ebb and flow. Compounding the error, Galileo mocked a proposal made by others, including Kepler, according to which the tides are caused by the attractive force of the Moon. This is of course perfectly true, though it would take Newton's theory of gravity to explain the phenomenon fully.

This should perhaps give us pause in assessing the epistemological clash between Galileo and the Church. Though Galileo was in the right, and had powerful empirical arguments on his side, one of those arguments was completely wrong. Though this is unlikely to make us more sympathetic to the Inquisitors, Urban, or even Bellarmine, it might make us reflect on the standards of truth being invoked on both sides.

Scholars actually disagree about this point, and in particular whether Galileo was still wedded to the Aristotelian scientific methodology he had encountered at the University of Padua. Certainly, Galileo did not feel any need to follow Aristotle as an authority. In one of his most eloquent expressions of this independence, he wrote, Aristotle was a man, saw with his eyes, heard with his ears, and reasoned with his brain. I am a man, and see with my eyes much more than he did.

As regards reasoning, I believe he reasoned about more things than I, but whether he reasoned better than I about those things which we have both examined will be shown by our arguments, and not by our authorities. Yet we've seen already that he claimed to be following Aristotle's lead by depending on empirical evidence. Some interpreters argue that he was also trying to employ a broadly Aristotelian method of proof, and to show that his arguments rose to the standards for demonstration set out in that method.

What would later be called the scientific method, in which a hypothesis is set out and then verified by experiment, would not count as a demonstration within Aristotelian logic. Instead, Galileo seems to have thought that in some cases empirical observation simply makes something immediately evident. This is why an experiment can establish a proposition as if it had been demonstrated.

This is what happened when he saw the phases of Venus through his telescope. He wasn't so much confirming the hypothesis that Venus is going around the sun as seeing directly that it does. It was in this spirit that he pronounced the new astronomy to be certain relative to other scientific endeavors that were merely probable. For example, astrology. This again should give us pause, in this case before leaping to identify Galileo as a forerunner of the scientific and philosophical developments that would come with the Enlightenment.

As I say, he was born in 1564 and he died in 1642, meaning that he lived about half his life in the 16th century and the other half in the 17th. That chronological happenstance underscores his status as a transitional figure.

Sometimes he does seem to belong to the 17th century, as when he argues that bodies in themselves have primary qualities like extension and shape, but not the sensory features that we ascribe to them like taste, odor, or color. These are, he says, nothing but empty names. If one removes the one sensing them, then all these qualities are taken away and annihilated. This will become a standard distinction in early modern philosophy.

Yet Galileo can also seem a creature of the Renaissance, sounding not unlike a Ficino or a Telesio when he compares the sun to the heart of an animal, suffusing, as it does, the whole cosmos with heat, much as the heart sends out heat to the animal's limbs. This philosophical view, he insists, is perhaps one of the principal doors by which one may enter the contemplation of nature.

The lesson we should take from Galileo is one we have already learned from discussing other scientists working around the turn of the 17th century, like Sennert, Gilbert, and Dee. Namely that, the study of philosophy in the Renaissance and Reformation is not just the ideal preparation for understanding early modern philosophy, it is already part of the study of early modern philosophy. And that is what we are going to start doing in earnest in a couple of episodes.

Back in episode 369, when I talked about Galileo's earlier career, I promised that I would return to him as a way of wrapping up coverage of the Counter-Reformation. Having made good on that promise, we're just about ready to move on to the delights of early modern European thought, beginning with a substantial series on philosophy in 17th and 18th century France and the Netherlands. Yes, we'll finally be getting to Descartes, Spinoza, and a whole host of other famous, and not so famous, names.

I know some of you have been waiting for me to get to this for years. If so, then I thank you for your patience and ask for just a bit more of it. Though Galileo was no fan of authority, I still think it would be a good idea to benefit from the expertise of an authority on his thought. And that's what we'll do next time, as we bring this current series to a close by talking to Eileen Reeves, here on the History of Philosophy, without any gaps.