 Hi, I'm Peter Adamson and you're listening to the History of Philosophy podcast brought to you with the support of King's College London and the Leverhulme Trust, online at www.historyoffilosophy.net. Today's episode, For a Limited Time Only, John Philoponos. Modern day scientists estimate that the age of the universe is 13.7 billion years. That's a very long time. You could watch every movie Buster Keaton made, even the talkies, and still be left with about 13.69999 billion years to kill. In fact, given 13.7 billion years, I could probably just about finish this series of podcasts on the history of philosophy. Well, if I pick up the pace a bit. And yet, as staggeringly large as this amount of time may be, it is as nothing compared to the age of the universe according to Aristotle. You could double it, triple it, or for that matter multiply it by one billion and get no closer. For Aristotle, the universe has already existed for an infinitely long time and will never stop existing. Moreover, the universe has always been pretty much the way it is now. It has always been spherical, with an outer sphere of fixed stars at the edge containing more nested spheres with planets seated upon them, and at the center, the region of air, earth, fire, and water inhabited by humans, plants, and animals, all of which are likewise eternal in species. Aristotle's commitment to an eternal universe was so emphatic that no ancient philosopher seriously questioned it. Convenient doubts about Aristotle's confidence would be raised only later by medieval thinkers like Maimonides and Thomas Aquinas. So for ancient thinkers, the question was rather, what about Plato? Some middle Platonists, notably Plutarch and Atticus, read Plato's dialogue Timaeus as endorsing a beginning in time for the universe, and were happy to say that on this point Plato was right and Aristotle wrong. But from Plotinus onwards, Platonists took this to be a misreading of Plato. Some, like Porphyry and other commentators on Aristotle, might have been motivated by their desire to make Aristotle agree with Plato whenever possible. But they had other reasons. If the physical universe is a necessary effect of transcendent causes, which give rise to it like shining lights or overflowing fountains, how could the universe be anything other than eternal? Thus all the figures we call Neo-Platonists accepted its eternity and also believed that, in doing so, they were in agreement with both Plato and Aristotle. Until that is, the year 529, when a Neo-Platonist named John Philoponus wrote a massive work arguing that the universe is not eternal and that Plato knew it. The treatise was called Against Proclus, reasonably enough given that it demolished a series of pro-eternity arguments collected by Proclus. The arguments given by Proclus drew not only on Aristotle's physical theories, but also on Platonist interpretations of Plato's Timaeus. For instance, in his first argument, Proclus argued that the world results from its creator's goodness or generosity, something implied in the Timaeus which says that the divine craftsman is not envious. Since the creator is permanently generous, the results of his generosity must likewise be permanent. Otherwise, the creator would change, suddenly acquiring the necessary generosity or ability to create which had previously been lacking. This was only the first of 18 arguments, which Philoponus refuted at immense length. Each of Proclus's arguments is set out in about a page or two, whereas the English translation of Philoponus's Against Proclus runs to four volumes. But wait, there's more. In another treatise called Against Aristotle, he tore into the arguments for eternity found in Aristotle's works The Physics and On the Heavens. The original version is lost but extensively preserved by the commentator Simplicius, who did to Philoponus what Philoponus had done to Proclus, quoting his opponent in order to refute him. Simplicius was not well pleased about Philoponus's temerity in attacking the great Aristotle. He compares his labors to the task of Hercules, who had to clean horse manure out of the largest stables in Greece. He uses various terms of abuse for Philoponus, but especially delights in calling him the grammarian. This is probably meant to call attention to the fact that Philoponus never headed a philosophical school and pursued a career on a lower rung of the educational curriculum. Yet this grammarian is now recognized as one of the most innovative philosophers of his era. His critique of Aristotle takes much of its power from his expertise in the texts he is attacking. Philoponus, like Simplicius himself, had studied at the feet of Ammonius in the city of Alexandria, though apparently not at the same time, since Simplicius claims never to have met his antagonist in person. And like Simplicius, Philoponus wrote a number of commentaries on Aristotle. Of these, some are apparently faithful recordings of the lectures of Ammonius. Others report on these lectures while occasionally weaving in Philoponus's own innovative ideas. And in fact, Philoponus continued to comment on Aristotle after he began his campaign against the eternity of the universe. What was his motivation? Certainly, he insists that Plato rejected the world's eternity. For many Platonists, that might have been reason enough to disagree with Aristotle, but not for Philoponus. In Against Proclus, he says that although Plato happens to have been right on this point, it is the truth that matters and not Plato's authority. He then provocatively lists a whole series of claims found in Plato that are just plain wrong. For some of these, Philoponus draws on his expertise in another field, medicine. Philoponus did not reject eternity because he was a Platonist, then. He rejected it because he was a Christian. Indeed, this may be the explanation of his nickname, Philoponus. It means lover of work, and given its length, Against Proclus alone would earn him that role. James Brown may have been the hardest working man in show business, but Philoponus was definitely the hardest working man in the eternity business. Still, the nickname probably has a quite different explanation. The term Philoponoi referred to certain Christians who had no clerical role but supported the cause of the faith and often agitated against the pagans in Alexandria. Our John Philoponus may have been a member of this group. We saw last time that pagan teachers like Ammonius frequently had Christian students, and that this relationship was fraught but often respectful. In Alexandria especially, pagans went out of their way to find common ground with Christians. To the examples I mentioned last time, we can add that Ammonius himself, who wrote a whole work to show that for Aristotle, God was a cause not just of motion, but of the very being of the universe, a thesis that was of course also dear to the Christians. It is likely no coincidence that Philoponus chose to break ranks in 529, the very year in which the Platonist school of Athens was closed down by an imperial edict. Perhaps he was bidding for the headship of Alexandria? If so, Philoponus failed. He was passed over for the pagan Olympiodorus. But Philoponus didn't need to be the school head to know his Aristotle thoroughly. This is the difference between Philoponus and other Christians who attacked the Neoplatonists on this same issue. In particular, two Christians from the city of Gaza named Aeneas and Zacharias had already written about the eternity debate. Particularly fascinating is Zacharias's work, a dialogue featuring as one of the main characters none other than Ammonius. In the dialogue, Ammonius is reduced to silence by a series of anti-eternity arguments. But in fact, though both of these Gazan thinkers had been taught by Neoplatonists, the arguments they mount fall far short of Philoponus's sophistication. Because the pagans offered numerous arguments for eternity, Philoponus has to fight on many fronts. Some of their arguments relied on features of the universe we see around us. Though Proclus does use arguments of this kind, they are mostly found in Aristotle. For instance, he had argued for eternity on the basis that the heavenly bodies must be made out of an ungenerated and incorruptible substance. The pagans also thought they could show that divine principles must give rise to an eternal universe. We already saw one such argument, Proclus's first proof which invokes God's generosity. And in general, Proclus is the main opponent when it comes to metaphysical or theological arguments for eternity. Aristotle, by contrast, is the main target when it comes to physics and the nature of the heavens. First then, let's see how Philoponus takes on Aristotle's physical arguments for the world's eternity. As I say, these invoked the unique characteristics of the heavenly bodies to show that these are bodies that can be neither generated nor destroyed. Aristotle thought this could be proved from the fact that the heavens move in a circle, unlike air, fire, earth, and water, which move in straight lines, either away from or towards the midpoint of the universe. The thing about circular motion, Aristotle observed, is that it has no contrary. For one motion is contrary to another if it begins where the other motion stops and stops where the other begins. But a circular motion starts and stops in the same place. If you walk in a circle, no matter how big or how small, you will always wind up where you started, something familiar to anyone who has ever gotten lost in a forest. Furthermore, things are always destroyed by their contraries. Thus, if the heavens move in circles, as they evidently do, they have no contraries and thus cannot be destroyed. This is ingenious, albeit perhaps not the most convincing bit of philosophy ever to flow from Aristotle's pen. Philoponus makes short work of it, pointing out that the contrary we are interested in here is not a motion in a contrary direction, but the complete absence of motion. What we are asking, in other words, is not whether the heavens can move a different way, like fire being forced to move down instead of up, but whether the heavens can come from, and be reduced to, non-existence. And here we get to the real core of Philoponus's disagreement with Aristotle. As we saw what seems like an eternity ago, Aristotle wrestled with the question of how to explain change without saying that things pop into existence from nothing or get destroyed into nothing. He agreed with pre-Socratics like Parmenides that such absolute change is impossible. Instead, he offered his analysis of matter and form. In any change, a surviving subject, the matter, gains or loses some feature, the form. For instance, if a stone becomes hot, nothing comes suddenly into existence or vanishes, a continuously existing stone simply gains a new property, namely heat. Philoponus wants instead to insist that God can create something from nothing. He cleverly adds that even in the kinds of change recognized by Aristotle, something does come into being from nothing, namely the new property that is gained. That is, even if a hot stone comes to be from something else, namely a cold stone, the heat that appears in the stone comes to exist after not existing. But Philoponus is only getting warmed up. So far, he's questioned a long-standing assumption of Greek philosophy that nothing comes to be from nothing. Now, he wants to question a newer assumption of Neoplatonists that Plato and Aristotle pretty much agree about everything. He points out that according to Plato's Timaeus, the heavens are not made of a special fifth kind of matter, as Aristotle thinks, but out of pure versions of the elements we find down in our world, predominantly fire. This brings us back to his other work of refutation, Against Proclus. There, Philoponus spends a lot of time on interpretive questions concerning Plato's dialogues, especially the Timaeus. He wants to show that Proclus was wrong not only about the world's eternity, but also in his interpretation of Plato. Proclus insisted that a divine cause, like the demiurge or the forms, cannot begin to produce their effects after not doing so. Philoponus retorts that this would make the causes somehow dependent on their own effects. Proclus, after all, seems to be saying that the causes are incapable of existing without producing those effects. And here, we've come to the real core of his disagreement with Proclus. Philoponus objects to the idea that God is forced to create a universe at all, that he produces what comes after him unnecessarily, as Neoplatonists have been saying since Plotinus. This explains Philoponus's relentless attention to the eternity question. He is trying to safeguard the idea that God freely bestows existence on a universe that would otherwise not exist. That underlies another typically clever move where he turns to his own advantage a passage in Plato that, at first, looks better for Proclus. Plato has the divine craftsman promise that the universe will never pass out of existence once it has been made. So, the universe is eternal, after all, at least in the future. But now Philoponus pounces. If the universe must exist at all times, past, present, and future, what is the point of having God promise not to destroy it? The passage confirms that for Plato, it is up to God how long the universe will exist. But in that case, mightn't God have decided, perhaps for reasons beyond our grasp, to create an eternal cosmos rather than one that begins to exist? To put it another way, if God can do anything, it looks like the universe might be eternal, or it might not. It's up to God. Here, though, Philoponus points out that God cannot do anything impossible, and it is indeed impossible that the universe has already existed eternally. His chief argument for this claim is as powerful as it is simple. If the universe were eternal, it would already have existed for an infinite time. But, an infinite time cannot ever finish elapsing, so we could never have reached the present moment. Here, he can yet again turn his enemies' weapons against them, because Aristotle himself said that infinity cannot be traversed or completed. This is why Aristotle was worried about Zeno's dichotomy paradox—remember the tennis court example. Zeno suggested that every motion, in fact, consists of an infinity of sub-motions. To this, Aristotle replies that a motion, or a distance, or a time, is only potentially divisible into infinity. You can cut it up as fine as you want, but you will never actually get an infinity of parts. Philoponus, thus, needs only to say that an eternal pastime would give us an actual infinity and not only a potential one. Even worse, it would be an actual infinity that is getting bigger all the time. The world has already existed for an infinite number of years, and each January, that infinite number grows by one. Since Aristotle rejected the possibility of actual infinities, or the idea that infinity could be increased, these look like devastating objections. Simplicius, however, responds that past eternity is in fact only potentially infinite. An actual infinity is one which is simultaneously present in its entirety—for instance, an infinite number of divisions that are actually made in a motion or a line. But past eternity is not like this, since the times and things of the past no longer exist. This debate, appropriately, is going to go on and on, finding echoes especially among philosophers in the Islamic world, some of whom adopt Philoponus's arguments, with others repeating Simplicius's replies. As for Philoponus, by the time he was done with the eternity debate, he had thoroughly undermined Aristotle's system of natural philosophy. This led him to make other adjustments to that system, of which I'm going to mention just the most momentous. In fact, it concerns the issue of momentum. What causes a moving object, like a thrown javelin, to continue moving? When you are in the act of throwing the javelin, and your hand is still in contact with it, obviously your hand is causing the javelin to move. But once it leaves your hand, it seems to be moving without being caused to move, at least until it lands on the ground some distance away. To avoid admitting that the javelin's motion is indeed uncaused, Aristotle devised the following ingenious, albeit totally false, theory. As it leaves your hand, the javelin is pushing air out of the way. The air needs to go somewhere, so it pushes back around the javelin until it winds up pushing the javelin from behind. After all, as the javelin continues flying forward, the space just behind it is available for the displaced air to rush in. Weirdly then, the javelin powers its own motion by shoving air back around itself and using this air as a kind of engine. The only reason the javelin can't continue flying indefinitely in this way is that the air resists being moved around. Hence, the javelin will fall back to the ground after a certain distance. In a related argument, Aristotle observed that the less resistance a moving thing encounters, the more easily and more quickly it will move. If this is right, then in a void, which offers no resistance at all, every motion should be infinitely fast. From this, Aristotle concludes that void is impossible. Philoponus is not impressed by these arguments and offers a new theory, which has been compared to the modern theory of impetus. In fact, Galileo will mention him by name in his own writings on motion. For Philoponus, things do not move because of any displaced air. He mocks Aristotle's theory by asking why armies don't launch javelins at their enemies using bellows to create gusts of wind. Rather, when you throw a javelin, you impress into the javelin a certain amount of power for moving. The javelin will move until the power runs out. All that air can do is get in the way. This means that motion could in fact occur in a void. If you threw a javelin in a void, it would go further than it does in air because there is no resistance, but it would still stop because you have not imparted to it an infinite power to move. This is not to say that Philoponus thinks that void really exists. In fact, he denies that it does. He just wants to insist that void is theoretically possible, and that motion would work just fine, in fact better, in a void than through mediums that offer resistance. Philoponus's innovative theory of impetus turns out to relate to his views on eternity. Since he rejects Aristotle's idea that the elements and heavens eternally move in straight lines and circles by nature, he needs to explain how it is that they do move. His answer is that God Himself imparts to these bodies whatever power they have. Thus, He makes all motion depend on God, as Aristotle had done, but in a much more direct way. God gives each thing its motion by giving it existence and a certain power to move. Though the universe has not always existed, Philoponus probably agrees with Plato that it will exist forever into the future. This is not because it has the natural capacity to be eternal, as Aristotle claims, but to the contrary, because God overrides the physical universe's natural tendency to corrupt. He gives it an unnatural, infinite power to continue existing and moving. In Philoponus, we have a man deeply engaged with the pagan philosophical tradition, especially the tradition of commentary on Aristotle and Plato. This is why I placed him here, as part of our examination of that tradition. But, as we have seen, his philosophy was motivated partially by his Christianity. He wasn't the only one. There were many philosophically-minded Christians in antiquity, and they will keep us busy for a good number of episodes. Before we leave the pagans, though, I'd like to look more deeply at Philoponus and the other commentators on Aristotle who produce the largest body of surviving philosophical writing in the ancient world. I'll be joined by a guest who knows better than anybody how large that body of commentaries is, since he's been instrumental in getting most of it translated into English. I hope this gives you an impetus to join me next time for an interview with Richard Sorabji here on The History of Philosophy Without Any Gaps.