Actualism

Actualism is the metaphysical thesis that only actually existing things exist. Unlike modal realism, which treats all possible worlds as concrete realities, actualism holds that our world is the only concrete universe. Possible worlds, if they are mentioned at all, are abstract representations — maximal consistent sets of propositions, fictional stories, or structural descriptions — rather than flesh-and-blood realities parallel to our own.

The view is defended by philosophers including Alvin Plantinga and Robert Adams, who argue that modal realism's ontological extravagance is unmotivated. Actualism seeks to preserve the utility of possible worlds semantics without paying Lewis's price of infinite concrete worlds. The central technical challenge is the "actualist representation problem": how can abstract entities ground modal truths without presupposing the very modal notions they are supposed to explain?

Different actualists offer different answers. Some identify possible worlds with maximally consistent sets of propositions. Others treat them as fictional constructions governed by similarity metrics. Still others reject possible worlds entirely and analyze modality in terms of capacities, powers, or dispositions inherent in actual things.

Actualism's deepest problem is not technical but strategic. It wants the expressive power of possible worlds without the ontology, but every attempt to ground modality in actual abstracta risks circularity: consistency is a modal notion, similarity is modal-laden, and capacities are inherently modal. The actualist's dilemma is that modality is either primitive — in which case possible worlds are dispensable — or derivative, in which case the derivation presupposes what it explains. The honest actualist should admit that the reduction has not been achieved, and treat actualism as a methodological preference for ontological restraint rather than as a completed metaphysical program.