 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.historyofphilosophy.net. Today's episode, The Constant Gardener, Epicurus and His Principles. Do you like a nice garden? Do you enjoy the company of friends? Do you believe the world is made of tiny particles, which you call atoms? Do you trust the evidence of your senses? Do you find politics tiresome and raise a skeptical eyebrow at those who live in fear of God? If your answer to these questions is yes, you might want to consider becoming an Epicurean. Membership has its advantages. This is a philosophy which is devoted to pleasure, though to be honest, you might be disappointed about that bit when you read the fine print. And while I'm being honest, I should warn you that it won't all be garden parties. There will be a regime of memorization and training to carry out. Oh, and if you do decide to sign up, then you'll want to clear a date each year to celebrate the birthday of your school's founder, Epicurus. Among the founders of the Hellenistic schools, Epicurus is the man we know best. We have only fragments and anecdotes to tell us about the founder of Stoicism, Zeno, and the first skeptic, Pyro. But for Epicurus, we have several extant writings, as well as a collection of memorable sayings intended to summarize his key teachings. We can thank our old friend Diogenes Laertius for preserving three letters of Epicurus, which deal respectively with his ideas about physics, cosmology, and ethics. Four more letters, including one addressed to Epicurus' mother, and some further sayings, have been preserved by another Diogenes. Yes, I'm aware that along with Diogenes the Cynic, this makes three men named Diogenes that I've mentioned in the last few episodes. Sorry about that. This latest entry in our ever-expanding Diogenes collection is Diogenes of Oinoanda, who like Diogenes Laertius lived a good half-millennium after Epicurus. Diogenes of Oinoanda was himself an Epicurean who paid to have teachings and texts of the school written up as a stone inscription, which has been discovered in modern-day Turkey. That shows something about the longevity of Epicurus' teachings. In letters to his friends and in pithy aphorisms, he encapsulated his doctrines in a way that was easy to study and memorize, and he explicitly encouraged his adherents to take advantage. This did the trick. Unlike his fellow hedonist Aristippus the Younger, who we looked at last time, Epicurus launched a philosophical school that would still be alive and well in the Roman Empire. The first century BC, the period which saw the fall of Rome's Republic, was also graced by Lucretius, whose magisterial poem On the Nature of Things set Epicureanism into verse. Maybe this was Aristippus' problem, he didn't have a good enough poet working for him. We'll look at Lucretius in a future episode. For now, and for the next couple of episodes, I want to concentrate on Epicurus himself and try to understand how his philosophy fits together. Like Plato and Aristotle, Epicurus had a sophisticated project, which had something to say on just about every area of philosophy, ranging from ethics to physics to the gods. Again, like Plato and Aristotle, Epicurus set forth his system in Athens. This was not his home city. In 341 BC, six years after Aristotle died, he was born on the island of Samos. And yes, that's the same Samos that produced Pythagoras. If you're still not impressed, the same island was the home of Aristarchus, a younger contemporary of Epicurus who was the first to propose that the earth goes around the sun, instead of the other way around. This part of the podcast was brought to you by the Samos Tourist Board. Epicurus moved to Athens in about 307 BC. Here he acquired a garden, which he could use as a base for his school. Significantly, this was located outside the city walls of Athens, which seems like a geographical shorthand for the Epicureans' lack of interest in political engagement. The Aristotelian ideal of practical, even heroic, action was not a flower tended in Epicurus' garden. Instead, this school was going to devote itself to a pleasant life of quiet philosophical discussion. That may give a false impression, though, because the Epicureans could be tenacious in defense of both the theories and the memory of their founder. The school would not have survived and prospered for hundreds of years had it not been willing to engage in polemics against other schools, and to foster loyalty by treating Epicurus himself as a literally divine figure. This is why they celebrated his birthday every year. The success of Epicureanism as a social enterprise is shown by that expensive inscription sponsored by Diogenes of Oenuanda. Not many philosophers have people paying to have letters they wrote to mom carved painstakingly into rock several centuries after they die. The success of Epicureanism as a philosophical enterprise, meanwhile, is shown by the fact that modern-day historians of philosophy find it worth dissecting every sentence of the precious remaining writings of Epicurus. So let's start to look at those writings, beginning with one of the letters preserved by Diogenes Laertius in his biographical collection, The Lives of the Philosophers. This letter is addressed to one of Epicurus' disciples, a man named Herodotus. The same name, but not the same guy as the famous historian. These Greeks clearly didn't have enough names to go around. Epicurus uses this letter to set out his physical theory, an atomic theory which harks back to the atomism of the pre-Socratic Democritus, but introduces some significant differences, as we'll see. In expounding this theory, Epicurus incidentally touches on another theme, which is where I want to begin—his ideas about human knowledge. Epicurus is an empiricist. He believes that sensation is the ground and source of all our knowledge. One of his collected sayings tells us that if we do not trust in sensation, we will have no standard against which to judge our beliefs. Epicurus is here raising, for the first time, a question that will dominate Hellenistic philosophy—what is the criterion of knowledge, which he calls the kanon, or measuring stick? His answer to the question is that all our knowledge ultimately derives from sensation and must be measured against it. This isn't to say that Epicurus is unwilling to go beyond the senses. After all, you can't see individual atoms, yet he confidently puts forth an atomist physical theory. But, he insists that claims about what is unclear to the senses need to be checked against sensation. He also uses analogies drawn for sensation for things that are not evident to the senses. Now, I know what you're thinking. Why should we put our trust in the senses? The answer is simple, according to Epicurus. They cannot be wrong. Your senses are infallible guides to the way that the external world is interacting with your body. Of course, this doesn't guarantee that you can avoid false beliefs. A classic Epicurean example is a square tower that looks round from a distance. Gazing at the tower, you might well form the belief that the tower is round. You'd be wrong, but this isn't the fault of sensation. That really is how square towers look from far away. If you see the world through rose-colored glasses, everything will look rosy. Again, sensation is not failing here. Rather, your experience shows you exactly what it should show you, given that you are wearing those glasses. Epicurus insists upon this point, worrying that if the senses are allowed to be false in some cases, there will be no end to our uncertainty. If they are always true, the senses can provide that yardstick against which we test all our beliefs. So we can discover that some beliefs are false, for instance, by walking closer to the tower and seeing that it is in fact square, but we can never discover the falsehood of the sensation itself, which gives rise to the belief. Sensation also gives rise to something more basic than belief. This is what Epicurus calls a preconception. The Greek word is prolepsis, one of the many technical terms Epicurus coined for expounding his theories. His idea is that sense experience gives us a range of rough and ready notions we can apply to the world. Our preconception of a giraffe might be animal that lives on the savannah, with spots and a long neck. This isn't a definition of giraffe, but it's enough to help you identify giraffes and start thinking about them more carefully. Preconceptions can form a basis for doing philosophy and a kind of check on the philosophical theories we develop. If we wind up giving a theory which violates our preconceptions, that will cast doubt upon the theory. Even more important is what Epicurus calls a common conception. This is a preconception that just about everyone shares, for instance that the gods are happy. These common conceptions are important because everyone will agree to them. They provide not just a starting point for philosophy, but an uncontroversial starting point. With this theory of preconceptions, Epicurus seems to respond to the problem Plato identified in his dialogue the Mino. As we saw, Mino's paradox shows that inquiry is impossible because we either know about the object of our search, or we don't. If we already know, there will be no point in inquiring, but if we do not, then how should we start trying to inquire? Epicurus' solution is not to invoke forgotten knowledge which is already in us when we are born, as Plato has Socrates suggest in the dialogues Mino and Phaedo. Instead, he proposes that by remembering our sense experiences, we build up preconceptions. These won't qualify as rock-solid knowledge, of the kind Plato was seeking, but they are good enough to get us going. Like Plato's category of true belief, they offer a kind of halfway house between certain knowledge and total ignorance. When we begin to inquire, we need not start from nothing. We can see these epistemological ideas put into practice in Epicurus' letter to Herodotus, as he defends his new version of the atomic theory. In setting out the theory, he's venturing into the territory of what he calls the unclear, or non-evident, so he needs to make sure that he stays true to sensation. First, he observes that nothing can be absolutely destroyed or generated. He agrees with Parmenides and his Eliatic followers that there is no such thing as a passage from being to non-being, or vice versa. If being could be reduced to absolute non-being, then being would disappear bit by bit until it is all gone. But look around, and you'll see that the world is still very much here. The basic building blocks of the world, then, cannot be utterly destroyed or made from nothing. On the other hand, Epicurus insists against Parmenides that the world does involve change. Again, look around. We see that there are bodies and that they are changing and moving all the time. To explain how this can happen, Epicurus makes a far-reaching theoretical point, which also seems to be grounded in sense experience. If a body moves, then it must move into an empty space, a place where there is no body. So we need to say that the world includes both body and empty space. This will be void, already a feature of Democritian atomism, albeit defended with a more careful methodology. We can imagine Aristotle turning in his fairly fresh grave, complaining that Epicurus' careful methodology hasn't stopped him from assuming what he should be proving. As we saw, Aristotle rejected the idea of void. He thought instead that the world is, as it were, full. Every time something moves, something else has to get out of the way. I push air out of the way as I walk, and it must flow around me and occupy the space I was just in, so that no space is left empty. Epicurus disagrees. He thinks that if the world were really full, nothing would be able to move, just as in a tin packed full of sardines, no sardine has any wiggle room. A world without void would be like the one Parmenides envisioned, static and unchanging. That may sound convincing, but it looks like Epicurus is assuming something Aristotle would not grant, namely that bodies must be unyielding. We could capture the disagreement by saying that Aristotle's conception of body allows it to be rather fluid, so that it can shift around to accommodate motion, whereas Epicurus assumes that all body must be equally solid and resistant, unlike void, which is completely unresistant and intangible. Notice that we are still talking only about bodies and void without claiming that bodies are made of atoms. But that's going to change now, which will annoy our ghostly Aristotle further, since he was a severe critic of atomism. For Aristotle, it is at least in theory possible to divide any body and divide again as many times as you like. This is what we sometimes call a continuous theory of body. No part of the body is too small to be cut. To be an atomist, at least in the ancient sense, is just to reject this idea that body is continuous. As we saw when discussing Democritus, the Greek word atamon means uncuttable, so atoms are simply parts of bodies that cannot be physically divided. Epicurus arrives at his atoms by considering something like Zeno's dichotomy paradox. If we allow every body to be infinitely divisible, every body will be made of infinitely many parts. But each bodily part must still have some size, so every body will be infinitely big. To prevent this absurd consequence, Epicurus embraces atomism. But this is going to be an improved atomism which benefits from being able to respond to anti-atomist criticisms like those presented by Aristotle. One challenge is to explain atomic motion. How can an atom be indivisible, argued the critics, if they are to move? Imagine an atom crossing a line. As it is doing so, the front part of the atom will be past the line, while the back part is not yet past the line. Oops. It looks like the indivisible atom is divisible after all. Or if you don't like that argument, how about this one? Imagine an atom being touched on either side, perhaps by two other atoms. Then it is being touched on its right part and on its left part, so it has two parts. It can be divided after all. Again, oops. Not so fast, says Epicurus. I didn't say that atoms are conceptually indivisible, only that they are physically indivisible. Atoms themselves are made of parts, just like bodies, but these parts cannot be physically separated from one another. He calls them minima, or minimal parts. These literally subatomic parts are quite simply the smallest possible size that there is. You cannot conceive of anything smaller. They do not have a left half and a right half, for instance. Also, when an atom moves, this will always mean that at least one minimal part has moved completely. You will never have a minimal part being only halfway over a line. Either the part is all the way over, or it hasn't crossed the line yet. Just think how much goal-mouth controversy they could avoid if they used minimal parts as soccer balls. Again, in support of his idea, Epicurus resorts to sensation. Having been born before the invention of soccer, he refers instead to the minimum body that we can see. Something like a tiny particle of dust has no visible parts, yet if enough dust motes come together, you have a pile of dust. In the same way, minimum parts have no sides or further sub-parts, but they can come together in some special way to form whole atoms. And come together they do, forming atoms of many shapes and sizes. How many shapes and sizes, you ask? Inconceivably many, says Epicurus. He doesn't admit what Democritus may have, namely that there are single atoms big enough to see. But there are all sorts of configurations of atoms, and as Democritus taught us, an infinite number of atoms. These come together to form larger bodies when they get caught in clusters, vibrating as they bounce back and forth, since atoms never stop moving in the void, but only change direction when they collide into one another. These complex bodies come together to form a whole cosmos. In fact, this happens many times. There will be inconceivably many worlds with all sorts of configurations scattered through the void, which is also infinite in all directions. This then is Epicurus' universe, an inconceivably large void, which lasts for infinite time and has infinitely many atoms, moving and colliding within it, forming bodies and whole cosmic systems scattered through unending emptiness. It's a breathtaking conception, albeit one largely familiar from his atomist predecessors. But Epicurus, unlike those predecessors, is fastidious about objections drawn from sensation. One objection is quite basic. When you drop something, why does it fall? Aristotle had explained this by saying that the heavy elements, earth and water, naturally seek a place towards the centre of the universe. But Epicurus' universe has no centre. So instead, he again improves on Democritus by proposing that all atoms have weight. Left to their own devices, they fall. The universe has an up and a down, even though it has no centre. This seems to suggest that when things are dropped in Australia, things should fall towards the sky. As far as I know, that doesn't happen, but Australian listeners can correct me if I'm wrong. That would explain how kangaroos jump so well. Leaving that aside, though, let's consider another objection. This one is from Aristotle. He observed that when things move, they go slower if they are moving through a denser medium. For instance, you move faster through air than water, and through water faster than mud. So, if you were moving through void, which has no density, you should move infinitely fast. I've said it before, and I'll say it again. Oops. Epicurus responds by holding simply that atoms all move at the same speed. You'll never guess how fast. Yes, inconceivably fast. Lucretius argues that this speed must be even faster than sunlight. After all, sunlight should be slowed down by collisions with the atoms that make up the air it is shining through, whereas an uninterrupted atomic motion will encounter nothing at all. The way Epicurus anticipates and responds to such objections shows how he is using sense experience to build his theory. He not only takes sensation as his starting point, he also uses sensation to check his theory, as he promised. If your theory cannot explain why things fall, then your theory needs work. On the other hand, Epicurus is happy to stick with a theory so long as it is consistent with sensation, in the sense of not being disproven. We want to believe things that are supported by sensation and avoid believing what is counter-witnessed, as he puts it. For instance, we might go up to the round-looking tower and realize that it is in fact square. Epicurus is not really in the Platonic and Aristotelian game of seeking certainty. Some degree of support and the lack of counter-witnessing is enough for him. He sometimes makes this explicit, especially when discussing less crucial points than the fundamentals of atomic theory. For instance, he allows several alternative theories to stand as being equally acceptable in cosmological contexts. This is not because he's lazy, it's because certainty about physics is not the goal of Epicurean philosophy. Rather, the goal is an ethical one. It is happiness, which he identifies with the absence of disturbance. And I have to confess that it would disturb me if you didn't join me for the next episode. Epicurus on pleasure and happiness, here on the History of Philosophy Without Any Gaps.