 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 University of London. Today's episode, The Harder They Fall, Galileo and the Renaissance. In the last episode, I suggested that we tend to overestimate, or at least misjudge, the psychological impact of Copernicus' removal of the Earth from the centre of the universe. By contrast, I believe that we tend to underestimate another feature of the new science of the heavens. Around this time, it became increasingly clear that the celestial bodies are not, as Aristotle would have it, perfect and unchanging substances made from a fundamentally different kind of matter from that found in our earthly sphere. The new science of the 16th and 17th centuries instead offered a single unified physics, applicable to both the heavens and the things around us in our everyday experience. Things up there are made of more or less the same stuff as things down here. And as we now know, outer space is full of changing and unexpected phenomena like comets, supernovas and Sandra Bullock. The unification of physics was already propounded by Telesio and Campanella. On their theory, the whole universe is made from one kind of matter, with everything from stars to stones being governed by the simple principles of heat and cold. But what they offered was indeed only theory. It was at the beginning of the 17th century that another Italian scientist offered what he at least considered to be direct proof. I refer, of course, to Galileo Galilei. He showed that the moon is not perfectly spherical but covered with irregularities and mountains on the basis of shadows he could see on the moon's surface using the new technology of the telescope. With that same instrument, he discovered that there are spots moving across the surface of the sun itself. Galileo also demonstrated that a nova that appeared in the night sky must lie beyond the moon, another example to show that things in the celestial world do change. Furthermore, his telescope delivered powerful confirmation of the Copernican theory, especially in the case of Venus. This planet could now be seen to have phases of illumination, just like our moon, something that could be explained only by saying that it orbits the sun and not the Earth. Galileo also found four of Jupiter's moons which were clearly orbiting around it. This was not a direct proof of Copernicus's heliocentrism but undermined a powerful argument for the ancient cosmology, given that the moon at least goes around the Earth, surely everything else does too. Given the presence of bodies orbiting Jupiter, it was now easier to believe that the Earth too might be circling the sun while having another heavenly body, the moon, circling it. Thanks to these and other discoveries, Galileo is rightly seen as a truly pivotal figure in the history of European science and philosophy. He literally saw things that no one had ever seen before, and as a result the universe as a whole came to be seen in a new light. If it takes one revolutionary thinker to appreciate another fully, then we might pay heed to the words of Immanuel Kant. In his critique of pure reason, which famously presents itself as performing a Copernican turn of its own within philosophy, he claimed that Galileo introduced an innovative scientific method, according to which, Now unlike Giordano Bruno, I would not insist that there is nothing new under the sun, but it's a guiding principle of this podcast series that intellectual developments do not come out of nowhere like the debris that caused all that trouble for Sandra Bullock in the movie Gravity. One reason it is worth our time to learn about supposedly minor authors is that it puts us in a better position to understand the achievement of more famous figures. And so it is here. There's good reason to see Galileo's breakthroughs, which he mostly made in the early 17th century, as a continuation of trends we have learned about from the 16th century. We can see this already from his proposal about just what it is that's causing the Earth and other planets to move along their orbits, namely a luminous warm fluid emanating outwards from the sun. This so-called caloric spirit sounds quite a bit like what we found in Telesio and Campanella. And Galileo had other things in common with other scientists of the Italian Renaissance. Like Campanella, Bruno, and Cardano, he was a practicing astrologer who was accused of believing in astral determinism and who cast nativities for patrons, friends, and even his own daughters. When he discovered moons around Jupiter, he argued for their importance on the grounds that their fast motion should make their astral influence particularly intense. And by the way, he didn't call them moons, but rather Medicean planets, named in honor of a patron who was a member of the Medice, everyone's favorite family of Florence. It doesn't get much more Renaissance Italian than that. But as it turns out, the strongest lengths between Galileo's thought and what came before had to do with precisely the feature Kant picked out as most new, namely his scientific methodology. A number of scholars, especially William A. Wallace, have argued that in this area, he was heavily indebted to the Aristotelian tradition, especially in the form represented at Padua by Jacopo Zabarella. After studying philosophy and mathematics in Pisa in the 1580s, Galileo taught there as a lecturer until he moved to teach at Padua in 1592. Studies of his early writings, which survive in Galileo's own handwriting, show that he was deeply schooled in the logic of the Paduan scholastics like Nifo and Zabarella. He seems to have been influenced especially by Jesuits at the Collegio Romano rather than by reading the Paduans directly, but he was widely read in scholastic literature and made numerous references to Thomas Aquinas and other medieval scholastics and also to Averroes. His studies convinced him that, even though Aristotle's physics was shot through with errors, he remained a reliable guide to best practice in science. Indeed, a favorite theme of his was that fidelity to Aristotle's method required departures from Aristotle's conclusions. He scorned the Aristotelians of his own day. Few of them inquire whether what Aristotle said is true, for it suffices for them that they will be considered more learned the more passages of Aristotle they have ready for use. In contrast to these slavishly traditional schoolmen, Galileo thought that a true Aristotelian philosopher was one who philosophizes according to Aristotelian teachings, proceeding from those methods and those true suppositions and principles on which scientific discourse is founded. In keeping with this, he insisted that if Aristotle were presented with the sort of observations made possible by the telescope, he would be the first to change his views on the nature and arrangement of the heavens. Indeed, in his treatise on the newly discovered sunspots, Galileo said that denying change in the heavens would be anti-Aristotelian, because it would involve departing from Aristotle's empirical method for the sake of preserving an Aristotelian doctrine in natural philosophy, even though the method is more fundamental. On the basis of such remarks, John Herman Randall Jr. already said way back in 1940 that in method and philosophy, if not in physics, Galileo remained a typical Padua-Nerus-Atellian. But much research has been done on this question since Randall wrote these words. It has shown that Galileo made flexible and innovative use of the scholastic methodology without departing from it entirely. In particular, he fused the method with extensive use of mathematics. As we know, there was also precedent for applying mathematical analysis to physical phenomena, stretching back to the Oxford calculators of the 14th century. Of more direct relevance was the humanist-driven study of Archimedes we discussed in episode 361. Thus, in an early work on the motion of bodies, Galileo said that he was adopting the methods of my mathematicians and praised the proofs of Archimedes as rigorous, clear, and subtle. Galileo was well aware that he was operating within the remit of the so-called mixed sciences in which mathematics is applied to nature. Archimedes with his attention to such phenomena as levers and floating bodies was the chief ancient authority for these disciplines. We can illustrate Galileo's method with his work on the problem of falling bodies. The first thing we need to understand is that this is really the same topic as the one just mentioned as in interest of Archimedes, namely floating bodies. After all, a falling body is just one that is not floating, and bodies can fall slowly in water just as much as they do quickly in air. For Galileo, floating is caused by balance, and falling is caused by imbalance. In a work called On Motion, written in 1590, he argues that bodies fall because of their relative heaviness, or gravity, compared to the medium in which they fall. By contrast, a body will float if it has the same gravity as the medium or less, like styrofoam floating in water. In a later work on floating bodies, Galileo sought to defend this account against an objection made by Aristotelians, namely that something heavier than water will still float in water if it is shaped the right way, like a broad, thin piece of ebony. This shows, they argued, that it is the resistance of water that causes bodies to float. Galileo retorted that the experiment involves a misleading appearance. In fact, trapped air is holding up the ebony, as we can see from the fact that the ebony will sink if it is forced below the surface. In further experiments using inclined planes, Galileo showed that a body falls with greatest force if it is moving straight down, with the force being reduced as the angle of fall is changed toward the horizontal by raising the surface along which the body is falling. So imagine a ball falling straight down, as opposed to rolling balls down a tilted piece of cardboard. The steeper the slope, the harder they fall. These experiments allowed him to discover the Law of Free Fall, showing that speed increases in relation to the square of the time of the fall, with the body accelerating faster and faster the longer it has been falling. It was precisely these experiments with inclined planes that Kant mentioned when crediting Galileo with the modern scientific method. But with all due respect to Kant, Galileo was not really using what has come to be known as the scientific method, that is, formulating hypotheses and testing them empirically. Rather, he was using the scientific method of the Paduan school. This meant working from observed phenomena back to fundamental explanatory principles, and then showing that the principles would explain the observations. In other words, he was using the method of regress described by Zabarella, while integrating mathematics into the different steps of that method. Or at least, that's the interpretation put forward by the aforementioned William Wallace. In favor of this reading, we can firstly note Galileo's own description of his goal as a search for underlying causes. Sometimes finding the cause is easy, you can infer it from just one observation. This is the case with the phases of illumination he saw in Venus, which immediately shows that it orbits the Sun. Already this is a thoroughly earthen point, since Aristotle says the same thing himself and about a different astronomical phenomenon. If we were standing on the Moon, we could immediately see that the cause of the lunar eclipse is the Earth blocking the light of the Sun. More complicated is Galileo's way of arriving at causal explanations that are not obvious. In the case of floating and falling bodies, the rule of heaviness was the right cause in his view. Experimentation was used simply to display the dependence of the observed effects on this cause. When he did things like testing how bodies float in water, or changing the inclination of a plane, on which balls are rolling, he was following a maxim he formulated as follows, The cause is that which, when it is posited, the effect follows, and when removed, the effect is removed. Though the earlier Padua-Nerus-Itilians did not propose using experiments in this way, doing so fits neatly into the theory of regress, which as we saw involved a step that Nifo called negotiation of the understanding. Here we have identified the cause but are trying to understand exactly how it works, before going on to affirm that the effects really do proceed from this cause. Galileo even makes a point familiar from Zabarella, namely that this stage helps show why the whole procedure is not circular. We do arrive at a cause on the basis of its effects, then explain the effects on the basis of the cause, but the intermediate step of considering and testing the cause allows us to understand the effects differently than we did at first. Galileo's use of the regressive method here helps to set his discoveries apart from what other mathematicians had done, like Guido Baldo del Monte, who as we saw also experimented with balls rolling on inclined planes. Unlike him, Galileo was able to identify what he called, Principles of Nature that are known and manifest, the sort of principles always invoked as the foundation of Aristotelian demonstrations. There's a further sign that Galileo does not use observations to test hypotheses, but to demonstrate the efficacy of his favored causal principles. This is the fact that he is surprisingly unconcerned about whether experiment actually bears out his theory. In fact, the inclined plane experiments never confirmed his laws perfectly because of the effects of air resistance and friction. Galileo dismissed this as irrelevant, saying that we should simply imagine doing it with an incorporeal tilted surface and a perfect sphere that contacts it at a single point so that there is no resistance. Such musings led him to the brilliant but untestable observation that in the absence of friction, even the slightest of pushes would suffice to move a body at rest in a horizontal direction since its weight would have no effect on lateral movement. On the other hand, experiment can disconfirm or refute causal explanations. This is why he proposed dropping objects off towers to show that the proportion of earth in a body would not make it fall faster as the Aristotelians claimed. And of course, sightings of the phases of Venus and mountains on the Moon directly refuted other Aristotelian doctrines. For Galileo, then, empirical demonstration is often just a matter of ruling out alternative explanations of a given effect, leaving his own causal account as the only one available. As he has one of the characters say in his famous Dialogues on the Two Chief World Systems, The primary and true cause of an effect is only one, and so I understand very well and am sure that at most one can be true, and I know that all the rest are fictitious and false. When a physical test is not possible, he finds other ways to reject rival theories, as when he wrongly argues that the tides are better explained by appealing to the motion of the Earth rather than the effect of the Moon pulling at the water. In this case, the tides are, as Galileo says, using scholastic terminology, a sign of the Earth's motion, which is in turn the cause of the tides. But this is a rather vulnerable position. If we are really proceeding by process of elimination, then we need to show not just that our causal explanation can account for the observed effects, but that there is no other causal explanation that could give rise to those same effects. This is something that was well understood by Galileo's opponents, not least in the church hierarchy. The papacy wanted him to retreat from his Copernicanism, at least to the extent of admitting that the new model was merely a possible or mathematically useful basis for astronomy rather than insisting that it was the exclusive physical truth. But like Bruno, Galileo rejected this easy way out. Of course, we now know that he was right about the facts and admire him for his courage in standing up for what he knew to be true, but by the epistemological standards accepted on both sides at the time, it's actually not so clear that Galileo did know he was right since this would mean achieving demonstrative understanding grounded in causal first principles. His style of proof by regress could discover a candidate cause for the observed effects, eliminate other proposed candidates, and then account for the effects in terms of his own preferred cause. But it could never show once and for all that no other explanation can ever be provided. Perhaps the true cause hasn't been suggested yet. Perhaps it is even beyond the human capacity of discovery. This was not a merely technical point. As far as the churchmen were concerned, scripture was the most reliable guide to the nature of the world since it was revealed by the God who made that world. They could point to biblical passages like one found in the Book of Joshua, in which the sun is miraculously commanded to stand still in the sky. What sense would this make if, as the Copernicans claimed, the sun is always standing still and it is the earth that moves around it? Of course, theologians were well aware that scripture was subject to allegorical and metaphorical readings, but why should they reject the clear meaning of scripture on the basis of scientific theories that fell short of absolute certainty, as codified in Aristotelian epistemology? Galileo himself thoroughly trained in the Aristotelian tradition likewise associated true science with total certainty. So where a scientist of a later age might have contented himself with simply asserting his theory as the best hypothesis discovered so far, he had to insist that his theories were established beyond all doubt. In some cases, human knowledge could, he claimed, reach a level of certainty matching even God's. Since he took such phenomena as the phases of Venus to have proved once and for all that the planets do go around the sun, Galileo demanded that interpretations of scripture be adapted to this empirical finding. He wrote that, In the case of the passage from the book of Joshua, he cleverly noted that the miracle in question would make even less sense within the Aristotelian understanding of the cosmos, where all the visible stars and planets are seated upon spheres that move one another in a coordinated fashion. According to this worldview, God could not have made the sun stop without stopping the whole system. In general, though, Galileo was rather unconcerned about possible clashes between the Bible and science, in part because they have different subject matters. The purpose of scripture is simply to tell us what we need to know for the sake of our salvation. He quotes a churchman who admitted that If scripture occasionally speaks as if the earth is unmoving, this is just to avoid confusing the common believer who assumes that the ground under his feet is at rest. And besides, all good Christians will readily agree that scripture is true. How then could it ever disagree with the demonstrated conclusions of science? Since these conclusions have been proven with certainty, they must surely be true, and it is impossible for one truth to conflict with another. Galileo is here repeating, more or less verbatim, an idea about scriptural exegesis put forward by that great hero of Aristotelianism, the Muslim commentator of Averroes. In his decisive treatise on the relation between reason and revelation, he had likewise argued that That work was not translated into Latin, so Galileo would not have known that he was reiterating a point made already by Averroes, but perhaps he would have appreciated the parallel. As we've seen, he saw himself as upholding Aristotle's scientific method while rejecting his scientific conclusions. Even toward the end of his life, Galileo was still insisting that he had always been an Aristotelian in matters of logic. By that time, famously, he had paid the price for following scientific inquiry wherever it led. He was condemned by the Inquisition in 1633, made to reject his own teachings and placed under house arrest. This is a story we need to tell in more detail. By exploring the text that got him into trouble, he aforementioned dialogues on the two chief world systems and the story of his trial. We'll be better placed to do that once we learn more about the historical background, and that's going to take a while. Galileo has given us a fitting conclusion to our coverage of the Italian Renaissance, and he will offer an equally fitting transition to the riches of 17th century philosophy. But we won't be able to make that transition properly until we understand much more about the age that came before. After all, plenty was happening outside Italy in this time, including the work of Copernicus and a small matter called the Protestant Reformation. So we will return to Galileo again after we have dealt with all that. In fact, I'll be devoting a whole series of episodes to cover the Northern Renaissance, the Reformation, and the backlash against Protestantism in Spain and Italy that is often called the Counter-Reformation. That's what's coming next after one final interview in which we, ironically, bring our time in Renaissance Italy to an end by visiting the Eternal City. Ingrid Rowland will be joining me to show why there's no place like Rome as we round off this series of episodes on Renaissance Italy by discussing humanism, the role of the Church in Roman intellectual life, and its persecution of figures like Giordano Bruno. Later on, the history of philosophy, without any caps.