In analytic philosophy, actualism is the view that everything that is (i.e., everything that has being, in the broadest sense) is actual.Actualism (Stanford Encyclopedia of Philosophy)Plantinga, Alvin (1976). "Actualism and Possible Worlds". Theoria 42 (1–3): pp. 139–160. . (Reprinted in his compilation Essays on the Metaphysics of Modality, Oxford University Press). Another phrasing of the thesis is that the domain of unrestricted quantification ranges over all and only actual existents.Woodward, Richard (2011). "The things that aren't actually there". Philosophical Studies 152 (2): pp. 155–166. . .
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 possible truth. This contingency is usually described by the statement "there is a possible world in which Sherlock Holmes exists". The possibilist argues that apparent existential claims such as this (that "there are" possible worlds of various sorts) ought to be taken more or less at face value: as stating the existence of two or more worlds, only one of which (at the most) can be the actual one. Hence, they argue, there are innumerably many possible worlds other than our own, which exist just as much as ours does.
Most actualists will be happy to grant the interpretation of "Sherlock Holmes' existence is possible" in terms of possible worlds. But they argue that the possibilist goes wrong in taking this as a sign that there exist other worlds that are just like ours, except for the fact that we are not actually in them. The actualist argues, instead, that when we claim "possible worlds" exist we are making claims that things exist in our own actual world which can serve as possible worlds for the interpretation of modal claims: that many ways the world could be (actually) exist, but not that any worlds which are those ways exist other than the actual world around us.
Viewpoints From an actualist point of view, such as Robert Merrihew Adams', possible worlds are nothing more than fictions created within the actual world. Possible worlds are mere descriptions of ways this world (the actual one) might have been, and nothing else. Thus, as modal constructions, they come in as a handy heuristic device to use with modal logic; as it helps our modal reasoning to imagine ways the world might have been. Thus, the actualist interpretation of "◊p" sees the modality (i.e., "the way" in which it is true) as being de dicto and not entailing any ontological commitment.
So, from this point of view, what distinguishes the actual world from other possible worlds is what distinguishes reality from a description of a simulation of reality, this world from Sherlock Holmes': the former exists and is not a product of imagination and the latter does not exist and is a product of the imagination set in a modal construction.Adams, R.M. (1974). "Theories of Actuality". Noûs, Vol. 8, No. 3, pp. 211–231. . .
From a modal realist's point of view, such as Lewis', the proposition "◊p" means that p obtains in at least one other, distinct world that is as real as the one we are in. If a state of affairs is possible, then it really obtains, it physically occurs in at least one world. Therefore, as Lewis is happy to admit, there is a world where someone named Sherlock Holmes lived at 221b Baker Street in Victorian times, there is another world where pigs fly, and there is even another world where both Sherlock Holmes exists and pigs fly.Lewis, D. (1986). On the Plurality of Worlds. Oxford: Blackwell
This leaves open the question, of course, of what an actually existing "way the world could be" is; and on this question actualists are divided. One of the most popular solutions is to claim, as William Lycan and Adams do, that "possible worlds" talk can be reduced to logical relations amongst consistent and maximally complete sets of propositions. "Consistent" here means that none of its propositions contradict one another (if they did, it would not be a possible description of the world); "maximally complete" means that the set covers every feature of the world. (More precisely: a set of propositions is "maximally complete" if, for any meaningful proposition P, P is either an element of the set, or the negation of an element of the set, or entailed by the conjunction of one or more elements of the set, or the negation of a proposition entailed by the conjunction of one or more elements of the set). Here the "possible world" which is said to be actual is actual in virtue of all its elements being true of the world around us.
Another common actualist account, advanced in different forms by Alvin Plantinga and David Armstrong, views "possible worlds" not as descriptions of how the world might be (through a very large set of statements) but rather as a maximally complete state of affairs that covers every state of affairs which might obtain or not obtain. Here, the "possible world" which is said to be actual is actual in virtue of that state of affairs obtaining in the world around us (since it is maximally complete, only one such state of affairs could actually obtain; all the others would differ from the actual world in various large or small ways).
Language and non-actual objects Actualism, the view that being is restricted to actual being, is usually contrasted with possibilism, the view that being also includes possible entities, so-called possibilia. But there is a third and even wider-ranging view, Meinongianism, which holds that being includes impossible entities. So actualists disagree with both possibilists and Meinongians whether there are possible objects, e.g. unicorns, while actualists and possibilists disagree with Meinongians whether there are impossible objects, e.g. round squares.
The disagreements between these three views touch many areas in philosophy, including the semantics of natural language and the problem of intentionality. This is due to the fact that various expressions commonly used in natural language seem to refer to merely possible and in some cases even impossible objects. Since actualists deny the existence of such objects, it would seem that they are committed to the view that these expressions don't refer to anything and are therefore meaningless. This would be a rather unintuitive consequence of actualism, which is why actualists have proposed different strategies for different types of expressions in order to avoid this conclusion. These strategies usually involve some kind of paraphrase that transforms a sentence with apparently problematic ontological commitments into one that is free of such commitments.
Names and definite descriptions Names of non-existent entities, like the 'planet' Vulcan, or names of fictional characters, like Sherlock Holmes, are one type of problematic expressions. These expressions are usually considered meaningful despite the fact that neither Vulcan nor Sherlock Holmes have actual existence. Similar cases come from definite descriptions that fail to refer, like "the present king of France". Possibilists and Meinongians have no problem to account for the meaning of these expressions: they just refer to possible objects. (Possibilists share this problem with the actualists in case of definite descriptions involving impossibility like "the round square") A widely known solution to these problems comes from Bertrand Russell. He proposed to analyze both names and definite descriptions in terms of quantified expressions. For example, the expression "The present king of France is bald" could be paraphrased as "there is exactly one thing that is currently king of France, and all such things are bald". This sentence is false, but it doesn't contain a reference to any non-actual entities anymore, thanks to the paraphrase. So the actualist has solved the problem of accounting for its meaning.
Intentional attitude reports Intentional attitude reports about non-actual entities are another type of problematic cases, for example "Peter likes Superman". Possibilists can interpret the intentional attitude, in this case the liking, as a relation between Peter, an actual person, and Superman, a possible person. One actualist solution to this problem involves treating intentional attitudes not as relations between a subject and an object but as properties of the subject. This approach has been termed "adverbialism" since the object of the intentional attitude is seen as a modification of the attitude: "Peter likes superman-ly". This paraphrase succeeds in removing any reference to non-actual entities.
Truthmaker theory and modal truths Truthmaker theorists hold that truth depends on reality. In the terms of truthmaker theory: a truthbearer (e.g. a proposition) is true because of the existence of its truthmaker (e.g. a fact). Positing a truth without being able to account for its truthmaker violates this principle and has been labeled "ontological cheating". Actualists face the problem of how to account for the truthmakers of modal truths, like "it was possible for the Cuban Missile Crisis to escalate into a full-scale nuclear war", "there could have been purple cows" or "it is necessary that all cows are animals". Actualists have proposed various solutions, but there is no consensus as to which one is the best solution.
Possible worlds