It is uncontroversially true that things might be otherwise than they are. … Ordinary language permits the paraphrase: there are many ways things could have been besides the way they actually are. … 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’. (Lewis 1973: 84)