Steve Pyke is a photographer that took a number of philosophers' pictures. He asked many of them to provide a few sentences about their approach to philosophy. David Lewis was one of them. He remarked:
"I am philosophically conservative: I think philosophy cannot credibly challenge either the positive convictions of common sense or the established theses of the natural sciences and mathematics."
In a famous book of his called Counterfactuals, Lewis writes:
"I believe, and so do you, that things could have been different in countless ways. But what does this mean? Ordinary language permits the paraphrase: there are many ways things could have been besides the way they actually are. I believe that things could have been different in countless ways; I believe permissible paraphrases of what I believe; taking the paraphrase at its face value, I therefore believe in the existence of entities that might be called ‘ways things could have been.’ I prefer to call them ‘possible worlds’" (page 84).
We discussed Lewis' ideas about possibility in my Metaphysics and Epistemology class. His view was that possible worlds are real and that they're just as real as the actual world. Here and here are more information about this view (now called modal realism).
Is Lewis' view philosophically conservative? Does he depart from the "positive convictions of common sense"? It doesn't seem conservative/like common sense to me. Of course, this doesn't show that his view is false. It's just not something that someone like my mother would propose as an explanation of possibility.
We only briefly touched on this in class, but a possible paper topic can be found here. I wonder what your thoughts are regarding modal realism and whether you think some alternative theory about possibility is more plausible. (This would likely have to be the long paper due at the end of the term, since it requires so much stage-setting and exposition.)
Here's one of the pictures that Pyke took of Lewis: