Thinking Well: An Introduction to Critical Thinking Book

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.