actualism

In analytic philosophy, actualism is the view that everything there is (i.e., everything that has being, in the broadest sense) is actual. Another phrasing of the thesis is that the domain of unrestricted quantification ranges over all and only actual existents.

The denial of actualism is possibilism, the thesis that there are some entities that are merely possible: these entities have being but are not actual and, hence, enjoy a "less robust" sort of being than do actually existing things. An important, but significantly different notion of possibilism known as modal realism was developed by the philosopher David Lewis. On Lewis's account, the actual world is identified with the physical universe of which we are all a part. Other possible worlds exist in exactly the same sense as the actual world; they are simply spatio-temporally unrelated to our world, and to each other. Hence, for Lewis, "merely possible" entities—entities that exist in other possible worlds—exist in exactly the same sense as do we in the actual world; to be actual, from the perspective of any given individual x in any possible world, is simply to be part of the same world as x.