On the Plurality of Worlds

by David Kellogg Lewis

This book is a defense of modal realism; the thesis that our world is but one of a plurality of worlds, and that the individuals that inhabit our world are only a few out of all the inhabitants of all the worlds. Lewis argues that the philosophical utility of modal realism is a good reason for believing that it is true.

Genres: Philosophy, Metaphysics, Nonfiction, Science, Logic, Physics, Theory

276 pages, Hardcover

First published November 1, 1985

About the author

David Kellogg Lewis was a 20th century philosopher. Lewis taught briefly at UCLA and then at Princeton from 1970 until his death. He is also closely associated with Australia, whose philosophical community he visited almost annually for more than thirty years. He has made ground-breaking contributions in philosophy of language, philosophy of mind, metaphysics, epistemology, and philosophical logic. He is probably best known for his controversial modal realist stance: that there exist infinitely many concretely existing and causally isolated parallel universes, of which ours is just one, and which play the role of possible worlds in the analysis of necessity and possibility.

-wikipedia

Reviews

[Steven · Rating 4 out of 5]

David Lewis was crazy. Crazy like a fox, maybe, but crazy. Completely brilliant, though. He gets 9.5/10 Berkeleys on the "This argument has an insane conclusion but I can't find the flaw in the reasoning" scale.

[laura · Rating 4 out of 5]

against all odds, i am extremely fond of this book. modal realism doesn't really do any of the work that i care most about doing, or resolve any of the questions that i care most about resolving, but i'll give this to david lewis, he seems to have done a great job of resolving the questions that HE cares most about, and with a combination of systematicity and whimsy unsurpassed in contemporary philosophy.

if your intuitions about modality, like mine, are deflationary, david lewis isn't going to change your mind. he can't justify our pre-philosophical intuition that things could have been different than they are, and he is explicit in his belief that it's not the proper role of philosophy to so justify. he's not out to justify modality, he's out to systematize it, work out a proper semantics for it, and he does an impressive job.

bertrand russell famously said that "the point of philosophy is to start with something so simple as not to seem worth stating, and to end with something so paradoxical that no one will believe it", and that's what lewis does-- fully spin out all of the zany implications of our modal talk, which is interesting no matter what your personal intuitions are. it's just good philosophy.

[Jesse Maurais · Rating 3 out of 5]

When trying to explain this book to friends of mine who are not initiated into the mysteries of philosophy, they very often conflate Lewis' modal realism with some variety of quantum physics. This is, of course, to misconceive Lewis' argument. Because he is in no way making a scientific claim in which we should believe in the "existence" of other possibilities than the actual on the grounds that it best explains observations. Rather, Lewis is suggesting that we should inflate our ontology with possible worlds--which are in every way as concrete as our actual world--merely because it makes other philosophical problems more tractable. In particular we should keep in mind Lewis' other work, Counterfactuals, which I would advise anyone to read first.

We might consider this an argument for parsimony. Modal realism is not without its cost, but Lewis is to argue that the cost is worth it. I'll return to the question of this cost momentarily but I feel there is a need to critique the fitness of this style of argument.

Reading this book, my mind kept going back to a grad course I took in the metaphysics of fundamentality. Though I would only fully realize why in the book's final chapter. The course I took considered the question whether there might be some most fundamental level of reality, beyond which we couldn't decompose matter into any smaller parts. Proponents touted the virtues of this theory: that it was, in some sense, simpler than one which has turtles all the way down. I wouldn't argue that simplicity is a virtue, among others, that theories possess. And despite the fact that this course was metaphysics from a post-positivist perspective, my own pre-theoretical biases kept reminding me why I tend to dislike metaphysics.

My chief problem with fundamentality, as well as with modal realism, is that whatever virtues that a theory may have, it has them just the same when the theory is true as when it is false. There either is or is not a fundamental level to matter; our searching after theoretical virtue does not help us close in on the truth. Similarly there either are or are not possibilia beyond our actual, and the virtues of modal realism, whatever they be, does not help us confirm the truth of the matter; modal realism has those theoretical virtues even if the theory is false.

You may freely disagree about the uses of virtue. Perhaps you have your own pre-theoretical beliefs about what qualities the truth should have. Perhaps the truth should be beautiful? Perhaps you are more pragmatic and expect the truth to be useful? Or perhaps you think that I'm missing the point; I should follow the course of Lewis' argument and not worry about whether we can confirm the existence of other possible worlds. I would maybe even take your advice if I were not so concerned with the unity of philosophy and science both together and within themselves. This would bring me back to the cost issues I had earlier postponed.

Do we really get modal realism at a bargain price? Lewis takes linguistic ersatzism to be the chief rival of modal realism. I was taught it by the name "canonical model" in my studies in modal logic, where worlds are maximally consistent sets of propositions. Lewis attributes to it 3 problems that he says his modal realism evades: 1) Some descriptions [of worlds] are inconsistent, so we need resources to distinguish the consistent ones; whereas there is no such thing as an inconsistent world. 2) We cannot have 2 indiscernible descriptions [of worlds]; whereas maybe there are indiscernible worlds. 3) What can be described is limited by what we have words for; whereas worlds can outrun what we have words for.

It seems to me that we can knock down 2 and 3 right from the beginning. If there are no other worlds than what are described then there are no indiscernible worlds, nor are there worlds to do the outrunning of words. To think otherwise is to judge ersatzism by the presumptive use of modal realism (that there are other worlds independent of our descriptions). There is no problem here.

A rebuttal of 1 is more complicated because one has to jump to several points in the book. Lewis believes A) that linguistic ersatzism (the canonical model) must but cannot dispel inconsistent worlds without resorting to primitive modal realism, and thus doesn't explain modality. B) His modal realism does not face this problem.

Start with A. The problem with ersatzism, he says, is that we have to explain inconsistency in modal terms. Specifically, he has us saying that it is not *possible* for all the propositions in a set to be true. However, I do not know anyone who worked with satisfiable sets of propositions who were aware that they were really doing modal logic. An assignment of truth values to propositions in a set will sometimes result in a contradiction. We can consider all combinations of truth value assignments and if there is at least one for which no contradiction is found then the set is satisfied and we call it consistent. Now, if Lewis wants to take this for possibility then I say we have defined modality in terms of all truth value assignments to propositions in a set. That is not taking modality as primitive. We certainly did not use modal terms in defining propositions, sets, or truth value assignments.

Now with B. Does modal realism evade responsibility for inconsistent worlds? The only mention of this that I could find while going back through the book (or the index) is very near the beginning. Most of the relevant discussion is found in a footnote. "To tell the alleged truth about the marvellously contradictory things that happen on the mountain is no different from contradicting yourself. But there is no subject matter, however marvellous, about which you can tell the truth by contradicting yourself. Therefore there is no mountain where contradictions are true. An impossible world where contradictions are true would be no better. The alleged truth about its contradictory goings-on would itself be contradictory... If worlds were like stories or story-tellers, there would indeed be room for worlds where contradictions were true. The sad truth about the prevarications of these worlds would not itself be contradictory. But worlds, as I understand them, are not like stories or story-tellers. They are like this world; and this world is no story."

If I am reading Lewis correctly then there are no impossible worlds because worlds are "real" things and real things cannot make contradictions, on his account. Whereas story-tellers like myself may as well admit contradictions because I can speak them. I will give this one to Lewis. If possibilities are "real" in his sense then there are none that manifest contradictions. It makes no difference to me. I do find it strange that I'm left paying the full bill, having to dispel inconsistent worlds, while Lewis eats free because modal realism dispels inconsistency by fiat. But actually I think Lewis is paying the same price for his lunch as I am. Perhaps even more. Why? Because modal realism really does weigh heavily against common sense.

This is what I meant when I alluded earlier to my concerns over the unity of philosophy. We take on the bloated ontology to evade dealing with primitive modality. Is it a deal? My suspicion is that the price works out the same, even if I thought I had to take modality as primitive, which I do not. My unity of philosophy is such that it bears the same weight no matter where weight is placed. Take a bucket of water out of one side of the pool and poor it in another. It amounts to the same. Take the burden off your semantics and put it into your ontology. Are you better off?

[Josh · Rating 3 out of 5]

Here Lewis defends modal realism (that there exists many possible worlds, not just abstractly but with the same level of reality as our world, that contain every possible possibility) through two main angles.

1) By virtue of its helpfulness in supporting and explaining such matters as modality, closeness, content and properties it should be supported in the same way mathematical postulations are assumed to be true if they help explain mathematical issues.

2) He defends modal realism from a variety of objections, some stronger than others. He addresses and/or modifies assumptions around modal realism to deal with these problems while maintaining the integrity of the possible worlds thesis. Some objections he replies to are the charge that modal realism strips the arbitrariness of our particular world, that it leads to moral indifference, and that it leads to skepticism.

The book is well written which makes reading it straightforward even when the discussions of modal logic and actuality get quite dense.

Personally I liked the book and the argumentation, but found it very firmly situated within the analytic tradition, and so, couldn't help but find it a bit dry and perhaps lacking in perspective in some areas.

[Mark · Rating 4 out of 5]

David Lewis puts forward an admittedly loopy philosophical "theory of everything": possible worlds (think parallel universes that we can't access) are real, out there, concrete. He is on board with how absurd his theory sounds and admits that he often gets gaping stares when explaining it. Nonetheless, I found it harder and harder to disagree with his theory as he works on dismantling opposing views throughout the book. Truly skillful and a testament to his brilliance. Not only is a universe of infinite possible worlds fun to think about, it's actually a philosophically practical way to imagine existence.

[Phill Melton · Rating 5 out of 5]

Insightful, brilliantly argued, and a salient warning on the dangers of following common sense principles to their logical conclusions. On Tuesdays, I agree with Lewis; every other day, I'm with everyone else in thinking him batshit insane. Lewis is a perfect model of modern philosophical writing, managing to be clear even in the most complicated of passages—which, seeing as this is a work of analytic metaphysics, are frequent. Modal realism may be crazy, but, as this book makes clear, there are good reasons for biting the bullet and disregarding the incredulous looks.

[Kramer Thompson · Rating 3 out of 5]

Lewis does a very nice job here explaining his theory of modal realism and arguing why it is superior to its competitors such that it should be accepted over them. A lot of this stuff is quite challenging and would be much more easily understood by those who have a solid background in metaphysics. The book is interesting and written well. Certainly worth a read for anyone interested in metaphysics, modality, or David Lewis.

[Matthew Adelstein · Rating 5 out of 5]

Lewis is unbelievably clever. He manages to, while defending a very implausible view, provide clever defenses of it and responses to objections. That said, however, I'm not a modal realist.

A first worry with the view is that despite Lewis's protestations, modal realism undermines induction. Lewis suggests it doesn't in any ways beyond those suggested by the standard problem of induction. But the standard POI can be avoided by suggesting that the world more likely to be actual is the simpler one. In contrast, if one thinks, as Lewis does, that all possible people really exist, then one should have an inscrutable credence in the continued success of induction--after all, there are infinite people with exactly your experiences, for whom the sun never rises. Why think you're one of the lucky ones? It seems dogmatic to think you're in an inductive world when there are just as many people in a non-inductive one!

Second, I don't think Lewis addresses the worry about epistemic access convincingly. How do we come to know about these far-away possible worlds? Lewis suggests this is analogous to the Benaceraff challenge, but I think there's an important sense in which one can grasp an abstract object but cannot grasp a literal planet--one that exists just as much as the table in front of me.

Third, I don't think Lewis successfully accounts for modality. Imagine that we discovered that the content of our model terms could be made sense of by referring to stuff on other planets. Maybe there happen to be things in the Andromeda galaxy that correspond to our model terms. That wouldn't be a successful reduction! Making the entities that fulfill our modal terms outside of our spacetime doesn't help the reduction! It doesn't matter whether they're just faraway in space or in a completely different region of space time.

I have more worries, but that's all for now!

[Pi · Rating 3 out of 5]

It's been a while since I've read some of Lewis' other works on counterfactuals and social conventions, which I very much enjoyed. This one, however, felt boring and repetitive. The writing still had the author's unique witty and diligent style, but seemed too contrived for the present me. All the linguistic-like analysis of various statements and concepts, intended to support the usefulness of the essentially a priori, metaphysical belief in the existence of an infinite number of causally independent but similar to each-other worlds and individuals, somehow didn't resonate with me. One shouldn't sacrifice falsifiability (due to its nature, the many-worlds thesis can never be empirically rejected) for instrumental usefulness (in answering a number of philosophical conundrums). Many-worlds can be a potent explanatory device, but one shouldn't read his metaphysics from his epistemology.

[Arthur Kyriazis · Rating 5 out of 5]

one of the most important books on philosophy ever written.

it has been enormously influential in both the academic and popular sphere. the entire notion of ontological parsimony has gone completely out the window in both academia and popular culture, to wit, the Matrix, Fringe, and the re-launch of Star Trek along a different path of time, e.g. a different possible world.

the notion of a plurality of possible worlds being ontologically and metaphysically real, and that those worlds should be given dignity, is due completely to Lewis. He struggled against the British analytic school for years.

And yet now, we see clearly what must have been clear from the outset--life presents a plurality of choices, and thus, a plurality of possible worlds.

[Chris · Rating 3 out of 5]

David Lews is an excellent metaphysician-logician, and not only that, but he holds the paradigm skill of an analytic philosopher. And, for that reason, I think the thesis in his book is largely engineered: his modal realism is like Berkeley's phenomenal idealism (in that they are both not correct, but hard to pin-point the fallacy)- it is definitely not correct, but since the authors of the theses are so clever, it is difficult to detect the fallacy in there arguments...

[Ethan]

I finished reading this months ago as of writing, but can't remember the exact date: May 6th it is.

Fundamentally Lewis seems to never get off the ground with the central idea here. In my view, to posit various concrete unrealised worlds as a way to create counterparts and to therefore talk about possibility faces intractable issues. It requires either a) solutions of striking cleverness from further academic work (of which there are many) that seem to lose the forest for the trees or b) a twisting and turning of one's mental frame into a mould that ultimately does not fit it.

The problem is, as Kripke and others have said for a while, is why should I care about a counterpart? A counterpart is not me. And it seems there is no interior logical connection to connect the one to the other. Even if I granted these counterparts it still remains very hard to link them in a kind of satisfying logic. As much as I admire Lewis' attempt to rid us of convoluted modalities and give us a logic of concrete objects to talk about possibility.

Further, and even more intractably I simply don't see how we establish counterparts in the first place. A change of eye colour here, a toe loss there, an event in one's life does or does not happen. The gradient is too vague, and I think this is one argument that falls into a genuine "slippery slope."

Lewis writes well, he even argues well, but the cost of the argument is much too expensive.

[George · Rating 5 out of 5]

Lewis makes things look deceptively easy, even though you require some background knowledge in metaphysics and language to fully get what he’s saying. Great for the advanced undergrad/grad student. Overall, seminal read in metaphysics.

[Alexander Smith · Rating 4 out of 5]

This book is surprisingly convincing considering how little I accept "common sense" arguments. A large chunk of this seems to adequately address some issues with Russell's analytic structures in acceptable ways.

[Louis Maez · Rating 5 out of 5]

Read this book on my first year of college for Theory of Possibility and Necessity. His arguments seem to draw an absurd conclusion, but they're difficult to overpower. Is the possible concrete and actual? Seems so.

[Kevin Connor]

I've read this back in my philosophy days; just too many other books crowding it out right now

[Philip Mlonyeni]

Vent heter han Kellogg??

[Meg]

he should have stuck with short stories rather than writing a novel (/j)

[Erin Seu]

"i only ask as a reward for my trouble, that whenever you see the sun, the sky, and the stars, you will think on me."

[Kaidi Pan · Rating 4 out of 5]

Genius.

[Ramzzi · Rating 4 out of 5]

“Some are deceived not about the future but about the past: they live in brand-new worlds full of false traces and records of a past that never was.”

“There are no gaps in logical space; no vacancies where a world might have been, but isn’t. It seems to be a principle of plenitude. But is it really?”

“[T]he time-shifting adverb, ‘now’ still refers to the time of utterance.”

“[W]hen something is arbitrary, we are apt to think that might well have been different.”

“Whatever the truth maybe, it isn’t up to us.”


Even if this book shall weave all possible arguments and logical rules to emerge the metaphysical possibility of the plurality of worlds—it can’t be recommended that immediately.

What I nevertheless triumph is that, analytic philosophy, at least has a great bet in matching Lewis Carroll, who happens also a mathematician-logician, almost an analytic philosopher, if he entertained solely philosophy during his time.

David K. Lewis arguably is a great bet with his kangaroos, philosophizing cat, neurons, stars to match Caroll’s wild, paradoxical, and whimsical rabbit hole where the world would never—to use Lewis’ term—“might have been.”

[Jimmy · Rating 4 out of 5]

Great book. In it, Lewis argues convincingly and defends modal realism. But no sane person can accept the ontology: infinitely many non-actual concrete possible worlds and individuals! The Lewisian account of modality is too costly to buy wholesale. Look to Kit Fine, not Plantinga, for a more grounded alternative: modal actualism. Nevertheless, this book is required reading for anyone interested in analytic philosophy.

[Erik Cameron · Rating 4 out of 5]

This book is great! This and Kripke's Naming and Necessity are two perfect introductions to analytic philosophy. Lewis can seem completely unhinged at first glance, until you get worked into his frame of mind. It's an excellent read for anyone curious about possibility and necessity.

[TheFIX · Rating 4 out of 5]

Not for the beginner! But other than that setback, it's proof that he was the finest philosopher of the latter half of the twentieth century.

[Martin · Rating 5 out of 5]

David Lewis FTW

[lucas · Rating 4 out of 5]

lewis is indispensable for contemporary philosophers.

[Matthieu · Rating 5 out of 5]

It's beautiful and rigourous and possibly (quite) wrong. Kripke attacked it because he was unable to grasp its deeper meaning(s) and implication(s)...

[Albert · Rating 3 out of 5]

Thought provoking, but often confusing and poorly argued. I'm not convinced by Lewis that something like linguistic ersatzism is a bad account of modality.

[M.k. Yost · Rating 5 out of 5]

Mind-blowing and not an easy read, but definitely worth it if you want to consider the possibilities/practicalities of other worlds.

[George Goodell · Rating 5 out of 5]

I think the incredulous stare might be a sign of how remarkable Lewis's philosophical ability is.