Modal Realism and the Existence of Possible Worlds
Modal realism is a view articulated by philosopher David Lewis to account for our modal discourse and posits the existence of possible worlds. Possible worlds are complete and isolated ways things could have been. What things? Everything, including the laptop I’m typing on, the chair I’m sitting on, the coffee I’m drinking, and my cat asking at this very moment to come inside (hang on… she’s inside). All that plus everything from the start to the end of everything (if there is a start and an end). Everything. But things could have been different. I could be writing this with pen and paper. I could have a dog instead of a cat, or a pet pig or pet rat. The Universe could have its fundamental constants set to values that don’t allow for life, and I wouldn’t exist. Pretty much everything could be different. All the ways everything could be different are possible worlds. For Lewis, what makes them possible is that they are consistent. Here logic plays a role, in ruling out worlds that are impossible because they are incoherent.
How does this account for our modal discourse? Our modal discourse is when we believe things to be possible or necessary. It’s possible for me to have a dog and not a cat. It’s possible for me to be writing this with pen and paper. Why? Says Lewis: because there are possible worlds in which I have a dog and not a cat, and in which I’m writing a blog with pen and paper (maybe it then gets transcribed by AI and posted on whatever the internet is and where blogs get posted in that world). It’s impossible, however, for me to be the first living thing to set foot on Mars and find bacteria somewhere on Mars. It’s impossible because that is the description of an inconsistent scenario, one in which I’m the first living thing on Mars even though there were already living things on Mars, a contradiction. So possible worlds can substantiate our modal discourse. So far, so good.
The incredulous step with Lewis is to argue for the real existence of those possible worlds. Why? Because they offer the best explanation for our modal discourse. One could think alternatively that they are a creation of the human mind, that they are a mere logical or epistemic tool, that they are linguistic entities, or that they aren’t necessary to make sense of our modal discourse. All those options, and others, have been entertained and defended at length by many a philosopher, and, says Lewis, none live up to the accuracy and simplicity of the belief that possible worlds exist. They exist in the same way our world exists. And their existence is what makes sense of our modal discourse. What do you reckon? The view is coherent. But is it cogent?
