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. Actualists face the problem of explaining why many expressions commonly used in natural language are meaningful and sometimes even true despite the fact that they contain references to non-actual entities. Problematic expressions include names of fictional characters, definite descriptions and intentional attitude reports. Actualists have often responded to this problem by paraphrasing the expressions with apparently problematic ontological commitments into ones that are free of such commitments. Actualism has been challenged by truthmaker theory to explain how truths about what is possible or necessary depend on actuality, i.e. to point out which actual entities can act as truthmakers for them. Popular candidates for this role within an actualist ontology include possible worlds conceived as abstract objects, essences and dispositions. Actualism and possibilism in ethics are two different theories about how future choices affect what the agent should presently do. Actualists assert that it is only relevant what the agent would actually do later for assessing the normative status of an alternative. Possibilists, on the other hand, hold that we should also take into account what the agent could do, even if he wouldn't do it. Example Consider the statement "Sherlock Holmes exists." This is a false statement about the world, but is usually accepted as representing a