The Man of Many Worlds, Part 3
S1: And my nation from slightly.
S2: If you ask David Lewis friends about his creative process, how he actually developed his views and put them down in print, they all tell a similar story.
S3: He didn’t drive for news in Australia.
S2: Frank Jackson Australian National University.
S3: So often I would pick him up to lunch from the airport.
S4: Back in those days, the drive took nearly an hour.
S2: Alan Hajek, also Australian National University.
S4: In other words, it was roughly the length of time it took to give a paper.
S3: I’d be driving focusing on the traffic and David would not.
S4: So let me try something out on you. Maybe it’ll pause. And then he began. We know a lot. I know what food penguins eat. I know that phones used to ring, but nowadays squeal when someone calls up and away he went, a
S3: whole series of paragraphs would emerge from his mouth, which would be the next major publication. And it just came out
S4: like that basically gave a very early version of elusive knowledge.
S2: He recites the entire essay pretty well.
S4: Yes, it was like he was taking dictation from God. You know, it just came out perfectly, formed first time roughly when we arrived at Melbourne University. He came to the end of the paper and I said, That sounds good to me, David. I think you better publish that.
S3: But a similar thing happened in our house, there’s a conference coming up. It was held our place for dinner. You hadn’t written the paper, so I hopped over in the corner in the dining room. Lots of noise going on. The children around my wife and I were cooking and he had that very distinctive black pin he used to run with. They sat down, wrapped the whole paper out on the whole pipe was in the mind or in the brain beforehand, just a matter of getting it down on paper.
S5: They say that experience is the best teacher.
S2: Here he is, dictating a paper from his mind in 1981.
S5: If you have a new experience, smell the skunk or taste the Vegemite, you come to know what it’s like. Whatever that means, but that isn’t the only thing that happens. You also gain abilities. You can recognize the experience if you have it again. You can remember having it. You can imagine having it. And you can also imagine having related experiences that you never did have tasting Vegemite, ice cream, for instance.
S2: On our third episode of The Man of Many Worlds, we’re featuring David Lewis’s most famous view that our universe is just one among an infinite number of other possible universes. He called the view model realism, and with the help of a few Australian and one American colleague, it had the effect of reviving questions in philosophy. Long thought to be unanswerable. The year was 1968. He was starting out as a professor at UCLA. Two things happened that year that would set his trajectory for the remainder of his career. One friendship and one rivalry formed together. They would turn David Lewis into the man of many worlds. David Lewis, his dissertation advisor at Harvard was Willard van Orman Quine. Quinn made his name as the most prominent American philosopher in the mid-20th century, arguing against things more than arguing for them. Quinn’s version of pragmatism, along with his empiricist roots, took the form of an attack on the ability of philosophy to make sense of human judgments about what is possible and impossible. For Quine, the world was full of what is true and false. And if things we see or hear or postulate to explain the true and false. What’s possible and impossible thought Quine wasn’t something objectively true out there in this universe or in any other. Sometimes Quine, as though possibilities were just defective notions worth abandoning and any serious thinking at best, he would say that they were features of someone’s psychology. If someone thought time travel was impossible, quaint thought, what this told you was that you were in the presence of a hard headed person. Someone who isn’t ever going to accept that there’s time travel, no matter the evidence they came across. Someone who thought time travel was possible was open minded about it, whether time travel was possible or impossible was not a question you could answer by inspecting or thinking of facts about the universe. They were psychological facts about how open or dogmatic a person was about their beliefs. Psychology izing philosophy was something central to Quine and the American pragmatist tradition. He was a part of. It would be a picture David Lewis would eventually overturn.
S6: I’m John Bigelow. I’m an emeritus professor at Monash University and I new David Lewis knew him well. I myself have worked in metaphysics primarily more or less the same areas that David Lewis worked in.
S2: John Bigelow traces the skepticism about metaphysics in Western analytic philosophy. Back to the Enlightenment, notably David Hume and Immanuel Kant, two figures that continue to shape philosophy in the West. Their skepticism came from very different places.
S6: Kant argued that we can’t decide the big issues we care about. The big issues are God freedom and immortality, and none of these can be decided by reason. So therefore, we should take a leap of faith because we can’t prove it either to be true or false, trying to put a full stop to arguing rationally about the big metaphysical issues that we care about from Kant right through under logical positivism, all the metaphysical questions. We’re supposed to be nonsense.
S2: The positive tests were the Vienna Circle, logical positive tests, heavily influenced by and impressed with David Hume’s empiricism and the burgeoning sciences of the early 20th century. Albert Einstein’s general relativity, thermodynamics and quantum mechanics. Science is so successful that comparatively philosophical questions look to them more like bullshit.
S6: It was the death of metaphysics and we were supposed to stop thinking about metaphysical questions and either do sensible empirical science or be an artist or something like that.
S2: Into that history comes Quine. Who, amongst other things, saw possibilities as another one of these metaphysical concepts like the South or free?
S6: Well, the Queen was still part of that wake of positivism. David Lewis had a respect for common sense that made him think that modalities got to be OK.
S2: Common sense judgments like you could have gone to the store, but instead you stayed home, and that’s why I’m mad at you. Modalities are claims about what you could have done and what things would have been like if you did them. We make them all the time. Respecting common sense for David Lewis meant respecting everyday talk and thinking as reasonable, sometimes true, and not to be deemed defective because there’s no science of the possible yet.
S6: Whereas Quine was willing to think of ordinary, commonsense beliefs as second grade discourse. You can talk that way just in the supermarket, but if you really want to live in reality, you just basically talk. Pure mathematics and high level physics is all you need, whereas David thought that that just can’t be right. In order to be a conscious agent at all, you have to sometimes survey the things you could do. That’s a modal claim possibilities and what the likely consequences would be of each of those things that you could do. And in the end, you only do one of them. So a lot of that reasoning was concerning things which are non actual.
S2: It’s counterfactual reasoning. It works when you think about the past or future. If you had gone to the store, we wouldn’t be out of milk now. If you go to the store now, maybe we can salvage this relationship. But if you don’t, I’ve had it with you, all of these are counterfactual hypotheticals about the world of possibilities, something Quine can’t houM. The entire tradition of philosophy they were in had rejected as being too weirdly metaphysical for rational discourse.
S6: It’s got to be sensible to be able to argue about possibilities. Quine doesn’t let you do that. Klein says you should just describe the world the way it is. How could we be conscious agents that make decisions and weigh up the possibilities and the probabilities if that’s all there was?
S1: I first heard of him from Peter Unger, who also went to Swarthmore
S2: philosopher Saul Kripke. He is credited along with David Lewis as the two figures who revived metaphysics in the second half of the 20th century through their work on language and its relationship to the concept of a possible world. They were colleagues for many years at Princeton, but their intellectual lives crossed quite a bit.
S1: Even before that, you were asking me when I first got to know him. This was when I was in the Society of Fellows at Harvard, and he was writing his PhD thesis on convention under Quine.
S2: Quinn also taught Kripke, who went to Harvard after that 1958 national science talent search. We talked about in the last episode the same talent search where most of David Lewis college friends met. As precocious as was David Lewis Saul, Kripke bypassed graduate school altogether, went straight to teaching in PhD programs before he even graduated college. When the two crossed paths at Harvard, they were working on completely non-overlapping projects. David Lewis on the conventions of language Saul Kripke John foundational issues in mathematics. But the historical record shows that both were thinking and developing views. Behind the scenes, unbeknownst to everyone else, about possibilities and possible worlds that would become their most well-known views. You kind of both emerged thinking about possible worlds and counterfactuals at the same time, but largely independently correct. And then you end up being at the same department.
S1: I think he knew about my modal semantics, which was very early, right? I managed to publish one of the papers before I got the college.
S2: There was a breakthrough idea that Kripke published before he got to college, an idea he kept working on despite repeated attempts to redirect him at Harvard. It’s about what possibilities are. It’s possible for Trump to have won the 2020 U.S. election, even though he didn’t, means that there is a possible world where he won that election. The fact that he won that election in 2020 in that possible world is what makes true in this world, that it’s a possibility here. There’s no possible world in which a pink raccoon won the U.S. 2020 election. That fact about a group of other possible worlds makes it true in our world that it’s impossible for a pink raccoon to have won the election. Kripke was able to give a description and then prove using logic that there was a complete and consistent way to translate all talk about possibilities and impossibilities into what happens at other possible worlds and how what happens at other possible worlds makes true possibilities and impossibilities in this world. What are possible worlds, in your view?
S1: There. Abstract entities,
S2: Kripke and probably everyone other than David Lewis thinks of possible worlds as a kind of device, an abstraction, a story of fiction. There’s something you can think about right about and even give a moderately complete description of, but they’re nothing more than that. Their descriptions, they’re objects of thinking, maybe even fan fiction about the actual world. But the actual world is special. It’s the only one that exists, the only one with actual planets, people, laws and flora and fauna in it.
S7: And Lewis could see already there.
S2: Anthony Fisher, University of Washington and David Lewis scholar
S7: that there was a lot of explanatory power that you can get from possible worlds, but these philosophers cannot be Kripke. We weren’t taking possible worlds seriously. The way that Lewis thought that we should take them, we should take them, as he says in some letters, as they are as a world, which is a big container. I very much like our universe. Lewis, in a way, is saying that possible worlds are no different in kind to our world. So this then points in the direction that possible worlds are concrete because our world is concrete.
S2: And these other concrete worlds are different from ours only and being inaccessible by space and time travel. No matter how far you go in any direction in space, no matter how far forward or backward in time you go. You will stay within your own possible world. That’s the definition of your world, a universe bounded by space and time. And the events in it. Possible worlds are disconnected concrete. Space and time universes with their own people, planets, laws and facts.
S1: Of course, David’s view was that there was no notion of actual world except the world. I happened to be in range
S2: for David Lewis. There’s nothing special about our world. Every world is actual to the people and aliens that live there. Actual is just the way people talk about their own possible world. David Lewis was convinced that this was the best way to think about possible worlds.
S1: One thing he had a certain amount of success with. For a moment here with me, as I remember it, is that this is the real end to it ever a natural view of worlds, right?
S2: But you didn’t stay convinced.
S1: And I know, of course it wasn’t. It limits mean by saying God created the best of all possible worlds. If there were all these destroying spacetime is there. What would God do to make one actual give it, I guess.
S2: It was 1968 David Lewis published a paper called Counterpart Theory and Quantified Modal Logic. His first paper that took seriously the metaphysical implications of the reality of alternate possible worlds, Kripke immediately wrote Lewis, a letter containing eight objections to Lewis’s view on the view that Kripke he likes going back to light that God only thinks about the other possible worlds. He could create a world in which I don’t exist or one where I teach at Swarthmore rather than Vassar. Those possible worlds are objects in the mind of God. Only in the act of creation does God make one of those worlds concrete and actual. But for David Lewis, all of those possible worlds exist concretely and must do so for there to be any possibilities at all. Counterpart theory was Lewis’s attempt to defend one metaphysical implication of his view. I’m here teaching at Vassar College. I could have been teaching at Swarthmore. In fact, I came close to accepting a job there many years ago. That means for Kripke that there’s a story you can tell a film that you could make a thought that you could have involving me teaching at Swarthmore. But for Lewis, it means there is a world, a concrete alternative universe in which I am teaching at Swarthmore. But given that I teach at Vassar, I’m not also somewhere else teaching at Swarthmore. That’s a contradiction. David Lewis, his solution is that I do not inhabit another world, a world in which I teach at Swarthmore. Instead, that world has a counterpart of me. It also has a counterpart of Swarthmore and a Vassar band of everything else in this world. Other possible worlds are made of counterparts of our world and counterparts of other worlds, and these counterparts are what make true, what’s possible for me in this world. That view that my possibilities are determined by what happens to counterparts of me, that concrete people living out their own lives, minding their own business in their worlds determine what is possible for me. That’s the view that just wasn’t acceptable for Saul Kripke.
S1: This idea of counterpart theory and destroying possible worlds always seemed to me to be so counterintuitive that I never was gripped by it.
S2: It was metaphysical theorizing that went off the rails.
S1: Once David got into something, he would not let go of it.
S2: But David Lewis had his reasons. As counterintuitive as modal realism and counterpart theory, why he thought the alternatives were even worse. Consider this puzzle I don’t have an identical twin brother, but I could have psychotic splitting is not an outlandish possibility on everyone’s view. That means there is a possible world in which I have an identical twin brother. In fact, there are a lot of these worlds infinitely many. But which of the identical twins in any of these worlds is me? This is called the problem of trans world identity. What if one of the brothers went on to teach at Vassar, but another went on to teach at Swarthmore? But that’s the guy who ended up producing a Slate podcast, High Five Nation. Am I the Vassar Professor Twin? Without the podcast or the Swarthmore professor with the podcast counterpart, theory does a much better job of answering this question. Neither is you, because you don’t exist in other possible worlds. There are two twin brothers. One is similar to you. In some ways, the other is similar to you and others. They’re both counterparts of you in different ways. There’s no fact in other possible worlds about which thing there is really you. The alternative view, where possible, worlds are just the story, which twin brother is really me is whichever one I decide is me. But that’s counterintuitive, too, if identity is just a matter of decision. Then why can’t twins in real life just decide to be the other one? I don’t mean just call themselves by the other name. I mean, decide that they will literally be the other sibling. In fact, actual identical twins make David Lewis case even better. I see twins every day at the bus stop. Let’s call them Abby. Like all identical twins, A and B are split from an original zygote. It’s a real nearby possibility that their zygote never split. That’s an even closer possibility than my zygote splitting into two. But in the possible world where it never split and it develops into only one person, is that person A. Or is that person be? There’s no answer. You can’t just decide that it’s a which makes b non-existent in that world and you can’t decide that it’s B. And do the same to A. Counterpart theory says that there’s no answer and no decision will give you an answer. This person is a counterpart of a. And a counterpart of B. And not the same as either of them. David Lewis thinks there’s no identity of people across different possible worlds. There’s only similarities between us and people in other worlds. The more similar, the more we’re counterparts.
S7: When Lewis argues for murder realism, he doesn’t say, I know with certainty that this view must be true. It’s not like that at all. The claim is this theory might be true, and this theory is most likely to be true when we compare it to the other theories that are on the table.
S2: Anthony Fisher is talking about the distinctive way that David Lewis argued for his metaphysical views. It was quite a departure from how philosophers historically did so. When someone complained that it was wildly counterintuitive to think that there are many other worlds just like ours, he’d listen to them and then issue a mark against his theory minus one. But then he would raise a puzzle for his competitors and make a mark for his theory, plus one and a minus one for his competitors. Quinn doesn’t think anything is possible or impossible. Minus one for him. Counterpart theory solves the problem of Transworld Identity, plus one for Lewis. No argument was decisive. No picture captured everything. All you had was competing pictures with their pluses and their minuses. And once all the pictures were on the table. The best view. The one with the most pluses and fewest minuses is the one we should believe. So I spoke to somebody very close to Lewis, but I won’t name who it was who as much as this person really admired Lewis and his views actually detested the. Appearance of cost benefit philosophy claiming something was a plus for a theory and a minus. And you add up the pluses and you take off the minuses and then that’s how you argue for something actually that played a big role in philosophy. People suddenly argued in that way. There was sort of gave license to people to argue in that way. Do you have an opinion about that argumentative strategy that they’re exhibiting of a theory and claiming it’s got more pluses and minuses and so forth?
S7: Yes, I think it is a good approach to metaphysical theorizing, and that’s because I think it’s a good approach to philosophical theorizing in general, and it’s also a good approach to theorizing anyway. Like for all domains, when we look at what scientists are doing, I think that they’re also engaging in this cost-benefit analysis. I think it’s got a humbling effect because. You are realizing that no theory is perfect. You are identifying costs not just in your opponent’s area, but in your theory. And you can also be charitable to your opponent because you can look at the benefits of their theory as well as sort of bringing up your own theory. We may, in the end, arrive at a table of adding up the pluses of the minus and so on where we get all the theories have a negative number. And then the question is which theory has the negative number closest to zero that I think represents the humility in his theorizing to we are going to find lots, of course, there’s no theory is going to be trouble free and we should never say things like my theory is the only theory that can explain this phenomena, and therefore it must be true those who don’t think like that. He didn’t argue like that. He thought that his theory was the best compared to others. But sure enough, some other theory down the road might be trouble free. Have the benefits of his theory, but not the costs. So he was open to that. So I think that a cost benefit analysis that way theorizing was also very productive for intellectual activity and for philosophical progress.
S2: It was always David Lewis goal to make philosophical progress, to piece together the most complete picture of the universe where everything fit together. He thought he found that picture in modal realism. He found other pieces fell into place. Once you accept it, when we come back, we look at those other pieces of the puzzle.
S8: I’m Helen Beebe, I’m a professor of philosophy at the University of Manchester in England.
S2: Helen Beebe was a co-director of the David Lewis Project at Manchester, which went through all of David Lewis correspondences. Lewis was perhaps one of the last 20th century figures to have primarily corresponded through hand typed letters sent through snail mail. The archive is the most accurate guide to the chronology of David Lewis philosophical thinking. His views about possible worlds developed out of problems that he wanted to address as far back as 1958. They were ideas he would eventually publish.
S8: He wrote one of the most important papers on causation in the 20th century, which is his nineteen seventy three paper, which is called causation.
S2: It was the concept of causation that pushed David Lewis to try and piece together a comprehensive picture of the universe. Causation had become a beguiling concept ever since philosopher David Hume convinced everyone in the seventeen hundreds that we never actually see it. The only thing we ever see, the only thing we ever sense is a correlation, two things happening one after another. Hume concluded from this empiricist that he was that whether one thing caused another, a virus causing a disease was a projection of our mind, something we convinced ourselves of with enough experience of correlation. That should be enough if you’re David Hume. Some things are projections of the human mind useful for us to believe and things we can’t help but believe. But whether there was any underlying reality to causes was not something for us to ever know. But ever the early met a physician, David Lewis wanted to know what causation really was, what underlying reality makes one thing cause another. It’s something he thought he figured out. As early as freshman year in college, my
S5: second paper in my first philosophy course defended the counterfactual analysis of causation. I’ve been at it off and on ever since
S2: David Lewis from 1999. The counterfactual analysis of causation is that A causes B means that if A hadn’t happened, neither would be. And if a were to happen, so would be.
S8: So now that just might not sound like rocket science, but it’s completely been the dominant view since, I think. Not that long after Lewis wrote that paper
S2: smoking causes cancer means the same thing that if the smoking never happened, neither does the cancer. And if the smoking had happened, you would find cancer. Hume himself flirted with the counterfactual analysis of causation enough to state it, but not enough to defend it. Hume liked the idea because he didn’t like the alternative, which was that causes are secret powers in nature hidden to human perception. Viruses cause disease on the secret powers of you would mean that viruses have a power within them that necessitates the disease makes the disease impossible to avoid. Given the right conditions. Hume rejected that human beings can ever perceive or sense in the world necessities and impossibilities. And could empiricist that he was. We can’t ever know the existence of things beyond our ability to sense them. The counterfactual theory of causation doesn’t identify causation with secret powers. But Hume and later empiricist, including Quine, probably recognize that you run into another problem. Where in the world do you look to sense what would have happened to a smoker if he never smoked? You can’t perceive something that hasn’t happened. Counterfactual hypotheticals are exactly that. Statements about things that haven’t happened.
S8: He first had the idea for counterfactual analysis of causation when he was 16 or 17. He kind of had some views about how counterfactuals might work in that paper, but he didn’t have it all straight, like, that’s a big job trying to figure out how counterfactuals work. And that was the thing that nobody really knew how to do in the late 1950s. He figured out a theory of counterfactuals in the late 1960s, and I think once he got that piece of the puzzle in place, it’s like right now I can sort out causation because that is my theory of causation.
S2: David Lewis modal realism came with a theory of counterfactual hypotheticals. Statements like thousands more people would have died if there weren’t any lockdowns. On David Lewis view, this statement means that in every possible world, a lot like this one where there were no COVID lockdowns. Thousands more people would have died. What makes a counterfactual true is what the concrete facts are in the concrete worlds that are very similar to our world. If you want to figure that out, you do what you do to try to figure out any concrete fact about a concrete world that you don’t know yet. What would happen if you grabbed a cast iron skillet with your bare hands after it’s been in a 400 degree oven for an hour? You never actually grab it, but, you know, through simulation, through past experience, through assumptions, you make just what the world would be like if you did do it. Since causation is just the counterfactual causes, we’re not about secret hidden powers in our world. They, too were about concrete facts in other concrete worlds. David Lewis liked the way all of his views connected. They hanged together in a comprehensive way. The reality of possible worlds meant the reality of true counterfactuals, which meant the reality of causation. And there was a lot more.
S7: One of the major concerns for Lewis was to explain the distinction between essential properties or accidental properties.
S2: What do you think is essential to you and what do you think you could lose and still be you? When I was a kid, I once refused to acknowledge my father because he shaved his moustache off, not realizing that facial hair is an accidental property. But what my mom lost all of her memories and then her consciousness recently. I started to let go well before the death of her body. It was because I recognized that those things may have been essential properties, so
S7: for Lois, for us to have that essential property, all of our counterparts must also have that property as well and accidental properties, properties that only some of my counterparts share in other counterparts don’t.
S2: The list of things that David Lewis could explain using concrete possible worlds started to multiply, mounting up pluses for his theory, convincing him that it was true. All of this came together for him, according to his letters in 1968, leaving him enough of a research program to last another 30 years. That was a lot of philosophy. So I want to end this episode with one last bit of biography that helps explain something that might have occurred to the attentive listener who’s made it this far into our series. Why are there so many Australian accents talking about David Lewis, a major American figure in American philosophy of the 20th century? It has a lot to do with arguably David Lewis best professional friend. Could you tell me a little bit about David Armstrong?
S9: Well, Armstrong, most people think is the greatest philosopher that Australia has ever produced.
S2: Peter Anstey is professor of philosophy at the University of Sydney and literary executor to the estate of David Armstrong.
S9: He was an enormously influential figure in the late 20th century. He was a fair bit older than David Lewis.
S2: When did he and David Lewis meet? When did the relationship begin in 1968?
S9: That’s the first letter is actually from Stephanie Lewis to David Armstrong. It’s a postcard of correspondence started and really continued until Lewis’s death.
S2: David Lewis and David Armstrong formed a relationship that Lewis and Quine never could. Neither rejected philosophical questions for being too metaphysical. Even though the two saw each other every year, their typewritten correspondence was enormous
S9: 690 pages, PDF files, a lot of the ballots to the friendship really was built around enjoying doing philosophy together. Some people like sailing together, then to David like philosophizing.
S2: Bigelow David Lewis views over the years would be developed in letters to David Armstrong. And David Armstrong’s views would be developed with David Lewis present,
S9: and then gradually they became closer and closer and shared much over and above philosophy, which is the Australian Bush Australian rules football. All these sorts of things in some sense. Do you need to view it as a kind of foursome? That Steffi was very much part of a picture, and so was Jennie Armstrong. That really helped things that the four of them got on as couples.
S2: This led to David and Steffi Lewis visiting and working out of Australia and also New Zealand every year during the Northern Summer’s. It would lead to him publishing many of his papers in his preferred journal, the Australasian Journal of Philosophy. A journal that continues to publish extensively. And what you might call in metaphysics. Some people argue that it even led to that journal and not the Croatian Journal of Philosophy, which is also in English being a high prestige journal today, completely due to the fact that David Lewis liked to publish in it because he liked the country and the country in turn liked his philosophy. And since then, generation after generation of philosophy, students from Australia and New Zealand reliably read David Lewis as undergraduates, something that cannot be said about philosophy in any other country. Next time on our final episode of The Man of Many Worlds,
S9: when David Armstrong heard that Lewis died, he went on the phone.
S2: We look at the last year of David Lewis his life.
S10: Hi Fi Nation is written, produced and edited by Barry Lam, associate professor and chair of philosophy at Vassar College. Executive producer of Slate Podcast is Alicia Montgomery, editorial director for Slate Podcast. Is Gabriel Roth, senior managing producer for Slate Podcast. Is June Thomas, managing producer for Slate Podcast is Asha Saluja, editor of Slate Plus With Me channel to production assistants this season, provided by Jake Johnson with the hi fi nation Dawg. For complete transcript show notes and reading list for every episode. That’s AHIP Nation Dawg. Follow hyphenation on Facebook and Twitter and at the website for updates on stories and ideas.