Modal realism is the view propounded by
David Kellogg Lewis that all
possible worlds are as real as the actual world. It is based on the following tenets: possible worlds
exist; possible worlds are not different in kind from the actual world; possible worlds are
irreducible entities; the term
actual in
actual world is
indexical, i.e. any subject can declare their world to be the actual one, much as they label the place they are "here" and the time they are "now".