If you picked up this book thinking a 'plurality' means, like, 7, then buckle the fuck up, kids.
Think of all the ways things could have been. The mundane ways, sure: you could have preferred tea instead of coffee, that lightbulb could have been blue instead of yellow, Steve Jobs could have founded Windows. Whatever. But shit could have been way crazier than that. We could have tentacles. Gravity could have been twice as strong. Geometry could be parabolic. Electrons could be replaced with - who the fuck knows, really.
Are you ready for the fun part? Because here comes the fun part: there are uncountably infinitely many worlds, and there's a world for every single fucking possibility. Remember how Hume said that nothing was ever necessarily connected to anything else? Yeah. As long as something doesn't contain any blatant contradictions, there is a world in which it's reality.
Of course, we can't get to these worlds, otherwise they'd be part of our world; they're completely isolated from our world in every way. "But surely our world is the real world?'' Fuck you. They're all real. You're not special and neither is your world - I have no clue what it would be like for them to be 'imaginary.' The only world I have any experience of is this one, and it's as real and concrete as can be. I bet they are too.
Look, I get it. You're, ah, incredulous - believe there are infinitely, uncountably many worlds as real as the world I'm in? At first, it sounds a little crazy. Except that - and here's the thing - it cuts through problems like a fucking scythe. Possibility and necessity? Fucking cake. If you want to know what's physically possible, just take every world where physics is the same as ours. If you want to know what's historically possible, just take every world with the same history as ours right up to whenever you have the question. Biology, chemistry, geometry, whatever. The problem of universal properties? Just the set of all things with that property in any world. Counterfactuals? Just look at the world most similar to ours where the antecedent is true. BOOM. Seriously, I can do this all fucking day.
So yeah, I happen to believe in a bunch of things. No, I can't prove their existence. But think of all the shit that you believe in without proof - 'redness'? 'Propositions'? Possible, imaginary worlds where, somehow as if by magic, Socrates isn't an ugly motherfucker? Even sets seem questionable - how could there be some universal object that contains all and only the odd numbers? But sets are useful as fuck, so we deal with them. Well, I say if you're going to make shit up, GO BIG OR GO HOME, bitches. If you think it's too crazy, whatever bro - not everyone is worthy. But don't come in my house, kick my dog, and tell me you have a simpler solution that you just made up where everything magically makes sense because your hand-waving said so. Mind tricks do not work on me, only ontologies.
So while you slave away trying to simplify your beliefs or build worlds out of words, as if coins can be minted by calling gold 'round', I'll be here with my sets and my concrete objects, solving everything and being awesome. Don't look at me like that - I'm right and you know it.
Get On the Plurality of Worlds on Amazon. Unless, that is, you're already a professor or a grad student, in which case your already thrice-highlighted and oft-consulted copy will do just fine.