David K. Lewis

Are there other worlds that are other ways? I say there are. I advocate a thesis of plurality of worlds, or modal realism, which holds that our world is but one world among many. There are countless other worlds, other very inclusive things. Our world consists of us and all our surroundings, however remote in time and space; just as it is one big thing having lesser things as parts, so likewise do other worlds have lesser otherworldly things as parts. The worlds are something like remote planets; except that most of them are much bigger than mere planets, and they are not remote. Neither are they nearby. They are not at any spatial distance whatever from here. They are not far in the past or future, nor for that matter near; they are not at any temporal distance whatever from now. They are isolated: there are no spatiotemporal relations at all between things that belong to different worlds. Nor does anything that happens at one world cause anything to happen at another. Nor do they overlap; they have no parts in common, with the exception, perhaps, of immanent universals exercising their characteristic privilege of repeated occurrence.

Michael J. Loux

The category of particulars includes what the nonphilosopher typically thinks of as "things" - familiar concrete objects like human beings, animals, plants, and inanimate material bodies; and the realist tells us that what is peculiar to particulars is that each occupies a single region of space at a given time. Universals, by contrast, are construed as repeatable entities. At any given time, numerically one and the same universal can be wholly and completely exhibited or, as realists typically put it, exemplified by several different spatially discontinuous particulars. Thus, different people can exemplify the same virtue at the same time; different automobiles can simultaneously exemplify the same shape; and different houses can, at a given time, exemplify literally the same color. The virtue, the shape, and the color are all universals.