Are Other Worlds Real, or Just Stories We Tell?
The Coin That Could Have Gone Either Way
You flick a coin. It spins, lands heads. You say, “It could have been tails.” That seems obviously true. But what makes it true? You might think there is an invisible, alternate world where it landed tails. Some philosophers have taken this idea so seriously that they built a whole theory of reality around it. Others found that embarrassing: they wanted to keep the language of “possible worlds” without having to believe in zillions of parallel universes. They invented a clever escape route: treat possible worlds as fictions, like Sherlock Holmes or ideal gases, that are enormously helpful but not literally real. This is modal fictionalism — the idea that talking about possible worlds is a kind of story-telling that lets us handle possibility and necessity without turning our universe into a multiverse.
When Philosophers Invented a Multiverse
The possible-worlds story grew popular because it gives crisp answers to hard questions. Suppose you want to know whether pigs could fly. You ask: is there a possible world where pigs fly? If yes, then possibly, pigs fly. If no, then it’s impossible. That simple trick works for all sorts of “could” and “must” claims. The philosopher David Lewis (1941–2001) took this literally. He claimed there are infinitely many concrete worlds, each a full-blown universe like ours, packed with people, planets, and flying pigs. If something can happen, there really is a world where it does.
That picture has a heavy cost. We only ever see our own world, so Lewis’s claim asks us to believe in an outrageous number of unseen things. His theory also says that merely possible objects — blue swans, the sculpture you never made, the coin toss’s tail outcome — exist somewhere else just as solidly as your chair. Many philosophers couldn’t swallow that. Yet they still wanted to use the possible-worlds way of reasoning. Could they keep the machine but throw away the ghost universes? That’s where modal fictionalism steps in.
The Story of Possible Worlds: How the Trick Works
The fictionalist says: we don’t need to believe in other worlds; we just need a story about them. Suppose you and I agree to tell a tale — call it PW, the fiction of possible worlds. Inside PW, there are countless worlds, each a complete cosmos. We then link ordinary claims about possibility and necessity to what the story says. The link is a two-way rule, a biconditional:
- Possibly pigs fly iff according to PW, at some world, pigs fly.
- Necessarily pigs don’t fly iff according to PW, at all worlds, pigs don’t fly.
When you say, “My coin could have landed tails,” you mean that according to the story, there is a world where that very coin came down tails. The literal truth is that no such world exists — the story is false in that flat sense. But the story is true in the fiction. This is like saying, “According to the Sherlock Holmes stories, there is a brilliant detective at 221b Baker Street.” The literal truth is that Conan Doyle’s detective never existed; the story-truth is something else.
The philosopher Gideon Rosen (in a 1990 paper) proposed using David Lewis’s own theory of possible worlds as the fiction. Lewis’s theory was meant as fact, but Rosen treated it as a useful yarn. Another philosopher, D.M. Armstrong (1989), suggested a two-step fiction: a “great fiction” that says there are many “little fictions,” each of which completely describes a single world. Armstrong liked this because it avoided the story saying that any world was just one of a crowd — each world could be thought of as the only one.
Modal fictionalists fall into two main camps. Strong modal fictionalists believe the fiction explains why modal claims are true: what makes “possibly, pigs fly” true is the fact that the story reports a pig-flying world. Timid modal fictionalists use the story only as a handy tool, not as an explanation; they think the real modal truths exist already, and the story is built to match them. The timid version avoids many headaches but leaves the deep question of what modality really is unanswered. The strong version tackles that question but faces sharper challenges.
The Trap Hidden Inside the Story
In the early 1990s, two philosophers — Stuart Brock and Gideon Rosen — independently spotted a trap. The fictionalist biconditional links necessity to what the story says about all worlds. Rosen’s chosen fiction, based on Lewis, says that at every world, there are many other concrete worlds. That is part of the tale. So, according to the fiction, at all worlds, “many worlds exist.” Using the biconditional backwards, that yields: necessarily, many worlds exist. And if it’s necessarily true, it must be actually true too. The fictionalist would be forced to admit that, literally, there really are many possible worlds — the very thing the theory was designed to avoid. The view seems to cancel itself.
This is the Brock/Rosen objection. Rosen himself later accepted a fix suggested by Harold Noonan. If the fictionalist carefully follows the exact “translation” rules that Lewis gave in 1968 for turning modal sentences into world-talk, the problematic step no longer goes through. The crucial difference is that a world can talk about other worlds without those other worlds being “inside” it in the sense the argument needs. So the fictionalist escapes the trap — if she is precise enough. Some philosophers still debate whether Noonan’s solution works in every version of fictionalism, but it gave the view a second life.
Too Many Stories? The Problem of Picking the Right One
A fiction doesn’t write itself. The fictionalist must choose a specific story about possible worlds and justify that choice. Armstrong picked his two-step tale; Rosen picked Lewis’s theory. But why that story and not another? Aliens, gods, or a cosmic computer could all be part of some fiction. The fictionalist needs rules — constraints — to narrow down the options. A timid fictionalist can say: pick whichever story matches the independently true modal facts. That’s no problem. A strong fictionalist, who wants the story to explain those facts, cannot lean on them. She must fix the fiction’s content using non-modal building blocks, otherwise the explanation is circular.
Further headaches pile up. Fictions have authors and seem a bit artificial. If modal truth depends on a story, does possibility disappear when no one is around to tell the tale? If all the stories that meet the constraints disagree on some detail, do some modal claims become neither true nor false? And what about incompleteness? The Sherlock Holmes stories don’t tell you how many hairs Watson had, and a possible-worlds fiction might be silent on plenty of details too. That could leave gaps in our modal knowledge that feel uncomfortable. Strong modal fictionalists must grapple with all of these worries. Timid fictionalists can sidestep most of them, but they lose the ambition of explaining modality from the ground up.
Why You Should Care About Fictional Worlds
Modal fictionalism isn’t just a game for experts. It’s an answer to a question you bump into every day. When you think, “I could have taken the bus instead of walking,” or “Things might have been different if I’d practiced harder,” you’re using modal talk. Fictionalism says you can take that talk seriously without imagining that a ghost-you in a ghost-world actually lived that alternative. The alternatives exist only inside a useful story — one we all implicitly share whenever we say “could have” or “must have.”
That matters because it shows how human beings use fictions to tame reality. Just as physicists reason about frictionless surfaces that don’t exist, we reason about other ways the world could be by telling stories of other worlds. Fictionalism lets us keep the powerful logical machinery of possible worlds while avoiding the weirdness of a bloated cosmos. It also keeps a live philosophical argument going: are we entitled to talk about possible worlds at all? Fictionalists say yes, as long as we remember we’re the storytellers. The next time you replay a choice in your head, you’ll be doing philosophy — and you can thank some very careful storytellers for giving you the words to do it.
Think about it
- If a scientist could predict every choice you’ll ever make with perfect accuracy, would it still make sense to say you “could have done otherwise”?
- Imagine a friend insists that Narnia exists because the story says so. How is that like or unlike saying a possible world exists because a modal fiction says so?
- Do you think it’s better to believe there really are other worlds where things went differently, or to treat those other worlds as just useful make-believe? Why?
