Absolute Actuality and the Plurality of Worlds

Let’s fix some terminology at the start. A world (or possible world – for me, the ‘possible’ is redundant) is, first, an individual, not a set or class; second, a particular, not a property or universal; third, concrete in this sense: it is fully determinate in all qualitative respects; and, fourth, a maximal interrelated whole: each world is internally unified, and isolated from every other world. There is at least one world, the world we are part of. It is an actual world, the actual world if there are no “island universes.” Worlds that are not actual (if any) are merely possible. A realist about possible worlds believes that there is a plenitudinous plurality of worlds: whenever something is possible – for example, that donkeys talk, or that pigs fly – there is a world in which it is true. There is more than one way to be a realist about possible worlds. Realists divide into two camps depending upon their account of actuality. According to David Lewis,