Extended modal realism

Extended modal realism is a metaphysical theory developed by Takashi Yagisawa. It concerns the question of what it means that something is possible or necessary. Modal realism is the view that besides the actual world, there are many possible worlds. They exist as alternate versions of the actual world we live in. It contrasts with actualism, which holds that there is only one world: the actual world. Extended modal realism is a special form of modal realism. It includes the controversial thesis that there are not just possible worlds but also impossible worlds. An impossible world is a world that contains a contradiction. Extended modal realism understands modality as a dimension similar to space and time. In this sense, a regular object, like a tree or a car, is not just extended in space and time but also across possible and impossible worlds: some parts of it exist in the actual world and other parts exist in non-actual worlds. There is only one universe encompassing everything that is real in the widest sense: the actual, the possible, and the impossible. Modal statements, like "Hillary Clinton could have won the 2016 US election" or "it is necessary that cows are animals", are part of everyday language. According to common-sense, some modal statements are true while others are false. Modal metaphysics is interested in what determines the truth or falsehood of modal statements, i.e. in what the aspects of reality responsible for this look like. Actualists maintain that reality is actual at its most fundamental level and that possibility somehow depends on or is reducible to actuality. Modal realists, by contrast, state that possibility is an irreducible aspect of reality besides actuality. The most well-known version of modal realism is due to David Lewis, who holds that a plurality of possible worlds exist beside the actual world. Every object just belongs to one world but it has counterparts in other worlds. The truth or falsehood of modal statements depends not just on the actual world but also on these other worlds.