 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, Sky Writing, Astronomy, Astrology, and Philosophy. What would it take for you to look at yourself in the mirror and think that you really ought to be the most powerful person in the known world? Perhaps you are fired by civic duty, a desire to help the people. Perhaps you've got connections. Your dad was the most powerful person in the world, and one likes to keep these things in the family. Or maybe you're just a megalomaniac who thinks untrammeled power over humankind is no less than you deserve. In the Roman era, a large number of people were led by such reasons to think that they ought to don the purple and become emperor. To be fair, some more or less had power thrust upon them, but most seized it eagerly with both hands, and often with an army as well. Occasionally, things got really out of control, as in 69 AD, also known as the Year of the Four Emperors. This, obviously, was a point in history when it didn't take much to make men see themselves as potential emperors. One of that year's four claimants, whose name was Otho, made a daring grab for power which included the brutal murder of his predecessor, Galba. Otho lasted only three months, but he did have an excellent reason to see himself upon the throne. Some astrologers told him he would be emperor. I guess they didn't mention the part about only lasting three months. Now, if you opened your newspaper today, turned to your horoscope, and read that this is a good week to declare yourself President of the United States, you presumably wouldn't drop everything and start writing your first State of the Union address. But the Romans took astrology more seriously than most of us do nowadays. Astrology had already played a role in imperial politics before Otho's day. Consider the following tale of two friends who went to consult an astrologer. The first friend was named Agrippa, and the astrologer prophesied that he was destined for an almost unimaginable greatness, a true prophecy given that Agrippa went on to win the battle of Actium and serve as the most powerful lieutenant of the great Augustus Caesar. After this, Agrippa's friend was reluctant even to hear his own fortune, which would obviously be far less auspicious. But when he finally gave his time of birth and the calculations had been done, the astrologer didn't even bother to utter a prediction. He simply fell at the man's feet, for this second man, named Octavian, would go on to be Augustus Caesar. That story is a legend, of course, but Augustus really did use astrology as part of his imperial image. He had his horoscope made public, and his star sign of Capricorn is found on surviving coins minted in his reign. What astrology could help give, astrology could also threaten to take away. Emperors often worried that astrologers or other diviners would declare that someone else was destined for power, undermining their authority. Ancient historians tell numerous anecdotes in which someone receives the dubious benefit of such a prophecy, and shortly thereafter, a death sentence from the capital intended to thwart the prediction. Social edicts were sometimes passed against the use of astrology to predict death, not coincidentally this occurred late in Augustus' reign, or against any use of astrology. Of course, there's not much point outlawing or censoring something no one takes seriously. Such laws are part of the abundant evidence that, along with magic and forms of divination, like reading the entrails of animals, astrology was a well-established part of the ancient worldview. So, for most philosophers, the possibility of successful astrological prediction, along with the power of magical spells, amulets, and so on, counted as what Aristotle would call an endoxon, a commonly held belief that could supply a starting point for philosophical reflection. If you think about it, it would be a pretty poor philosopher who, living in a society where astrology was widely accepted as genuinely efficacious, would just shrug and decide not to think about it. If the stars really do indicate future events, this stands in need of explanation. Astrology was particularly interesting for philosophers because, unlike magic or reading entrails, it was inextricably linked to a major branch of philosophy, namely cosmology. We have seen before that the heavens were a source of a continuing fascination for ancient thinkers. It is a major theme among pre-Socratics – you might remember Heraclitus' claim that the sun and moon are bowls of fire – and in Plato's Timaeus. Aristotle wrote an entire treatise called On the Heavens. These philosophers predated the widespread belief in astrology in the Mediterranean basin, which seems to have begun only after Alexander's conquests and the exchange of ideas between the Greek and Babylonian worlds. But by the 2nd century AD, it was possible – one might almost say inevitable – for the leading ancient expert in astronomical theory to write also about astrology. This author was Claudius Ptolemy. His mathematically sophisticated presentation of the heavenly system lived on for centuries, especially in a work we call the Almagest. Its name contains a hint of its historical influence. Originally, called the mathematical systematic treatise, it was often referred to simply as He Megiste, the Great Treatise. This passed directly into Arabic as Al-Majuzi, and the beginning of the English title Almagest simply retains the definite article Al from the Arabic. I can't resist mentioning that a similar etymology underlies the word alchemy, which comes from an Arabic transliteration of the Greek hemiye, the same word that underlies our word chemistry. Ptolemy didn't write about alchemy, but he did compose an extensive work on astrology, simply called the Four Books or Tetra Biblos. He thus embodies a more general ancient phenomenon, the intimate connection of practices we now usually consider disreputable with intellectual disciplines that live on in our universities. Alchemists availed themselves of Aristotelian chemistry, that is, the theories of elemental transformation he set forth in works like On Generation and Corruption. Magic could be explained using ideas from Stoic and Platonist physics, in particular the idea that the whole cosmos is like a single organism. The parts of the universe relate like parts of a body, so that they are capable of being jointly affected, in Greek sympatheia, another word that lives on in English as sympathy. This same idea was used by the Stoics to explain astrology, while authors like Ptolemy borrowed heavily from Aristotle's four-element theory and his cosmology. We might expect that astrology would be a good match for Stoicism. After all, the Stoics were determinists who believed that the natural order is an inevitable unfolding of divine providence. The possibility of foretelling future events fits nicely with this theory, but as it turns out, the Stoics were slow to embrace it with any enthusiasm. One passage in Cicero does suggest that the early Stoic Chrysippus accepted the following example of a conditional statement, If someone is born at the rising of the dog star, he will not die at sea. But again according to Cicero, Diogenes of Babylon, the Stoic representative in the famous embassy of philosophers to Rome in 155 BC, allowed only limited efficacy to astrology. Things really got going only with Poseidonius, a Stoic who was known to Cicero personally and is mentioned in Cicero's work on divination. Poseidonius seems to have accepted astrology and other forms of divination as a welcome confirmation of the Stoic determinist theory. His interest in the topic may relate to his famous construction of a model of the heavens, an armillary sphere. Despite this, it was the Aristotelian cosmic theory that appealed to the later Ptolemy and that would go on to be assumed by philosophically inclined astrologers and astrologically inclined philosophers even into the Arabic tradition. As you'll recall, Aristotle assumed, as did nearly all ancient cosmologists, that the earth sits at the center of a spherical cosmos. At the edge of the cosmos is the sphere of the so-called fixed stars. Since the earth is assumed to be unmoving, this sphere is taken to be revolving swiftly around the earth once per day. In this outermost sphere and our earthly world are more transparent spheres, in which the visible planets are embedded. From night to night, they change their position against the revolving background of the fixed stars. Now in fact, the earth is of course tilted on its axis and it is not only spinning around once per day, but also traveling around the sun once per year, give or take a leap day now and again. This means that the sun seems, if you suppose the earth to be unmoving, also to be moving relative to the fixed stars, describing a motion along a circle that is at an angle to the celestial equator. This motion of course takes one full year to be completed, and the inclined path the sun travels is called the ecliptic. The angle of the ecliptic was credited with the change of seasons. The sun's path does slip very slightly from year to year, a phenomenon called the precession of the equinoxes. This is in fact due to the wobble of the earth spinning on its axis. Ptolemy said the effect was only about one degree per century. The fact that ancient astrologers were aware of such a subtle change shows how observations and measurements were being made over the course not only of years, but of generations. A more obvious phenomenon, which can be seen even within a single year, is that the planets do not look like they travel stately circles around the earth. After all, they are in fact moving in elliptical orbits around the sun, just as the earth is. Rather, from the point of view of the earthbound observer, they sometimes appear to stop and go backwards. So it's patently obvious that the planets, including the sun and moon, are not moving in perfect circles around the earth. This was a problem for anyone who, like Aristotle, believed that the planets are seated in rotating spheres. He had to introduce multiple movers for each sphere to explain the irregular motions of the planets. A later expedient was the epicycle. The planet sits upon a much smaller rotating sphere embedded within the sphere rotating around the earth. The planet is like a dot on a spinning marble which is inside a big rotating glass sphere. This lesser spinning motion explains why the planet sometimes appears to move backwards. Another device was the eccentric sphere. A planet-bearing sphere could have a center other than the midpoint of the universe, something impossible to reconcile with the physical picture of nested celestial spheres. As is clear from such attempted corrections, it was vital to Aristotle and Ptolemy that the heavens remain a world of perfect circles. The non-circular motions observed had to be explained as the product of multiple interacting circular motions. This provided a contrast between heavenly bodies and the four elements in the world here below the heavens, air, earth, fire, and water, which have rectilinear motions. The light elements, air and fire, move up, and the heavy elements, water and earth, move down. In other words, the light elements move away from the heavy elements towards the midpoint of the universe. This gives Aristotle a basis for his claim that the heavens are made of an entirely different kind of substance, the so-called fifth element, which is eternal and indestructible. Ptolemy appreciates the exalted status this implies for the study of the stars. At the beginning of his Almagest, he argues that there is no greater theoretical discipline. He agrees with Aristotle that theology must study the ultimate mover of the heavens, which is divine. Sadly, a full understanding of this first cause of motion exceeds the grasp of humankind. Meanwhile, natural philosophy, which considers the world of four elements below the sphere of the moon, deals with things subject to constant change. So, these disciplines are imperfect. Theology, because no adequate comprehension is possible, physics, because there can be no stable understanding of unstable things. By contrast, when we consider the heavens on the basis of their motions, we are doing mathematics, a study that combines feasibility with perfectly stable objects of knowledge. As Goldilocks might say, not too ambitious, not too modest, but just right. Ptolemy strikes a Platonic note by adding that the study of the stars will bring our souls into a kind of order that imitates the perfect order of the heavens. The same point was made in that favorite dialogue of the late ancient world, the Timaeus. But none of this gets us from the science explored in the Almagest, which we would call astronomy, to the much more ambitious and contentious practice of astrology. Astrologers used horoscopes to predict the fates of individuals, and they also pronounced on the outcomes of more particular events, advising on everything from the best time to take a journey to the result of illnesses to the winners of chariot races. How is this possible? Here we can borrow from Tony Long, our interview guest from a few weeks ago, who has written of the difference between hard and soft astrology. Hard astrology claims that astral bodies actually cause things to happen, down here in our world. Soft astrology says that the stars merely signify future events without causing them, making prediction possible for those who know how to read this sort of sky writing. As we've seen, the Aristotelian Alexander of Aphrodisias balked at the idea that the stars cause everything to happen down here. For the stars, with their perfect and eternal motions, partake of divinity. And, let's face it, a lot of what happens down here is really unfortunate. The wrong people become emperors, children refuse to finish their supper, the giraffe enclosure just happens to be shut the day we visit the zoo. To put the blame for such things on the stars would be blasphemous. Astrology was criticized more directly by representatives of other philosophical schools. The inscriptions of Diogenes of Oneonta include an attack on astrology, unsurprising given the Epicureans' dislike of Stoic determinism. Sextus Empiricus and other skeptics likewise refuted astrology. They too were opposed to Stoicism, and, of course, ancient skeptics were in the business of refuting pretty much everything anyway. An amusing anti-astrological argument was offered by the early academic skeptic Carnaides. If time of birth determined one's fate, then everyone who dies in a huge battle must have been born at the same time. As Christianity came to dominate late antiquity, astrology itself became increasingly embattled. Authors of no less standing than Augustine tried to refute it. For instance, he used what was by his day a very old argument not unlike that of Carnaides. If the moment of birth decides one's fate, then identical twins should have the same fate, but this isn't true. The much earlier Christian thinker Origen seems to have admitted soft astrology. The stars do signify future events without causing them. Having held out this concession to astrology, he snatched it away by denying that humans are able to read these signs. But even for Christians, things were not always so clear-cut. Origen thought he had to admit that stars serve as signs because of a passage in the book of Genesis, and there were other religious reasons to allow that stars do serve as messengers from God. Just think of the star shining over Bethlehem at Jesus' birth, a story which has been seen as the Christian equivalent of Augustus using his horoscope to support his political legitimacy. Of course, philosophy could be used not only to critique astrology but to support it. A remarkable example is the poem called Astronomica by an otherwise unknown author named Manilius. Taking inspiration from Lucretius and, perhaps, from the Stoic Poseidonius, Manilius put complex mathematical accounts of the heavens into torturously difficult Latin verse. This is the first complete theoretical work on astrology to survive from antiquity, and it almost went lost, barely surviving through the medieval period, only to be rediscovered in the Renaissance. Far more influential was our new friend Ptolemy, who not only adopted a broadly Aristotelian cosmology in the Almagest, but also called on the resources of Aristotelian physics in his astrological work the Tetra Biblos. Aristotelian cosmology had always faced the difficulty of explaining how the heavens exercise influence on the earthly realm. You don't have to believe in astrology to wonder about this. The sun and moon have evident effects on the seasons and tides, and, in fact, astrologers presented their theories as a mere extension of this kind of phenomenon. But Aristotle denied that the sun is hot. So how does it warm us? He flirted with the possibility of invoking friction, but this makes little sense, given that the sun's sphere is separated from our atmosphere by the impenetrable and presumably heat-proof sphere containing the moon. Ptolemy did not really solve this problem either, but simply associated various planets with certain elemental properties. The sun was of course heating, albeit not hot, while the moon causes moisture, hence the tides, and so on for other planets. Like other astrologers, he linked such properties to more obviously metaphorical ones, claiming, for instance, that the moon is feminine and the sun masculine. As standard in ancient astrology, he also made the effects of planets depend on their location in the zodiac, their relative position to other planets, and so on. While this may all make Ptolemy sound like an unashamed hard astrologist, he hedges his bets by insisting that astrology deals only with probabilities. The stars do cause, but in so complex a way that we cannot be sure of our forecasts. Thus, he compares astrology to medicine. Both are beneficial to mankind, but neither offers absolute certainty. We can find similarly nuanced views among critics of astrology. A century after Ptolemy, Plotinus took a great interest in astrology, devoting a treatise to the topic and discussing it at length in other treatises. Like Alexander, Plotinus worries about making the divine stars causes of evils, and about the deterministic implications of astrology. So he sometimes seems to deny the stars any causal role at all, at one point sarcastically comparing this suggestion to the idea that birds make future events occur, an allusion to the ancient practice of divination based on the flight of birds. On the other hand, he explicitly speaks of the stars as a kind of writing that signifies the future. This makes his view seem like a clear case of soft astrology. In fact, though, his position is more nuanced than that. In one of many borrowings from Stoicism, Plotinus accepts that the universe is bound together by a kind of sympathy. This gives him a physical basis for allowing some causal influence from the stars upon our world. His considered view does allow this, but only to some extent. For instance, the positions of the stars at the time of our birth may influence our ethical dispositions, but they do not predetermine our actions. This is not only because the stars are only part of a more complex cosmic causal system, but also because our souls are immune to influence from mere bodies, even divine heavenly bodies. We'll see why once we turn our attention to more fundamental aspects of his philosophy. But, as a good Plotinus, Plotinus would encourage us to prepare for this by getting a solid grounding in mathematics. So, next time, I'll be looking at ancient mathematics and its philosophical significance. I know I can count on you to join me for an interview with an expert on this topic, Serafina Cuomo, next time on The History of Philosophy Without Any Gaps.