Actualism

Core Idea and Basic Contrast

Actualism is a metaphysical thesis about what there is. At its core, it holds that everything that exists is actual, and that there are no entities—objects, worlds, or states of affairs—that exist in a merely possible, non-actual way. All quantification in ontology (“there is something such that…”) is, on this view, quantification over what is actual.

The central contrast is with possibilism and with modal realism.

• Possibilism maintains that there are possible but non-actual entities (such as merely possible people or events) that exist in some broader sense than actuality.
• Lewisian modal realism famously claims that other possible worlds exist as concrete realities, just as real as the actual world, differing only in indexical relation to us.

Actualists reject such additional domains. They typically allow talk of “possible worlds” only as a façon de parler that can be reinterpreted in terms of actually existing entities—most often abstract objects like sets, propositions, or maximal consistent states of affairs.

Historical Background

The roots of actualist ideas can be traced to classical metaphysics, particularly the Aristotelian distinction between act (actuality) and potency (potentiality). For Aristotle, only what is in act is fully real; potentialities are grounded in actual substances. Although Aristotle is not an “actualist” in the later technical sense, his framework privileges actuality as metaphysically fundamental.

In scholastic philosophy, the notion of actual being (esse in actu) is often opposed to merely potential or possible being. God is characterized as actus purus (pure act), the fullness of actuality without unrealized potential. Possible beings were usually understood as ideas in the divine intellect rather than as independently existing non-actual entities.

In the early modern period, Leibniz introduced the influential vocabulary of possible worlds. For Leibniz, all possible worlds are logically or conceptually real in God’s intellect, but only one—the best possible world—is actualized by God’s creative choice. Thus, while he grants a substantial status to possibilities, he sharply distinguishes the single actual world from all other merely possible ones.

The explicit term “actualism” gains prominence in the 20th century, particularly in modal logic and analytic metaphysics, where the question “What do our quantifiers range over?” becomes central. Philosophers such as A. N. Prior and others working in tense and modal logic begin to speak of actualism as a thesis limiting quantification to the actual domain.

Actualism in Contemporary Modal Metaphysics

In contemporary debates, actualism is a technical stance about modal ontology:

1. Domain of quantification
   Actualists maintain that all quantifiers—whether inside or outside modal operators—range only over actually existing entities. When we say, “There could have been a talking donkey,” we are not thereby committing ourselves to an additional, non-actual talking donkey somewhere in a merely possible realm.

2. Reconstruction of possible worlds
   To preserve the usefulness of modal discourse, actualists typically reconstruct possible worlds as abstract objects that exist in the actual world. Examples include:

   • Maximal consistent sets of propositions (or sentences).
   • Maximal possible states of affairs.
   • World-books: complete descriptions of how reality might have been.

   On such views, there are many possible worlds, but they are all actual abstract objects, not concrete alternate universes. The “actual world” is then often identified with the one possible world that correctly describes reality.

3. Plantinga-style actualism
   Alvin Plantinga influentially defends an actualist account of modality in terms of states of affairs and essences:

   • A state of affairs is an abstract actual entity that may obtain or fail to obtain.
   • A possible world is a maximal state of affairs—one that includes, for every proposition, either it or its negation.
   • What is possible is what obtains in at least one of these maximal states of affairs.

   For Plantinga, everything that exists (including states of affairs and worlds) is actual, but not everything obtains. This allows modal language without non-actual beings.

4. Finean and neo-Aristotelian actualism
   Kit Fine and other neo-Aristotelian metaphysicians develop versions of actualism in which essence, structure, or grounding in the actual world underwrite modal truths. Instead of building modality primarily on possible worlds, they treat facts about what things are—their natures—as more fundamental. This approach remains actualist because it never quantifies over non-actual entities, but derives possibility from the essential features of actual ones.

Debates and Criticisms

Actualism faces a number of well-known challenges and has generated extensive debate.

1. The problem of merely possible individuals
   Critics ask how actualists explain statements like “Napoleon could have had a twin” or “There might have been another person very much like you who never existed.” Possibilists claim that such statements naturally refer to non-actual individuals. Actualists must instead:

   • Treat these as claims about ways actual individuals could have been (counterfactual properties), or
   • Rephrase them using descriptions and abstract surrogates (e.g., maximal properties or essences) without positing non-actual people.

   Some argue that these reconstruals are artificial or revisionary; actualists reply that they are metaphysically cleaner and avoid an inflated ontology.

2. Expressive power vs. ontological parsimony
   A common defense of actualism is that it offers ontological parsimony: it does not multiply realms of being beyond the actual. Modal realists respond that their view gains theoretical simplicity and explanatory power by taking possible worlds as concrete and straightforwardly real.

   Debates often turn on whether the additional complexity of actualist reconstructions (via abstract “ersatz” worlds, essences, or world-books) undermines the claimed parsimony.

3. Cross-world identity and counterpart theory
   Under modal realism, David Lewis uses counterpart theory to explain how an individual in one world is related to similar individuals in others. Actualists, who only have one concrete world, often maintain a more traditional notion of transworld identity: the same individual could have been different, and these modal profiles are captured by properties it actually has (such as having certain essential or accidental attributes).

   Critics question whether this actualist approach satisfactorily accounts for all our intuitions about modal identity, while defenders argue that it better matches ordinary thinking than the counterpart-theoretic alternative.

4. Logical and semantic frameworks
   In modal logic, actualist and possibilist quantification lead to different formal systems. Questions arise such as:

   • Should the domain of quantification be fixed across possible worlds (actualist or constant-domain semantics)?
   • Or can the domain vary, including individuals that are not in fact actual (possibilist or varying-domain semantics)?

   Actualists typically favor constant-domain or actualist-friendly semantics, sometimes supplementing them with special predicates (e.g., “actually exists”) to distinguish between being in the domain and existing in a stronger, metaphysical sense.

Despite these disputes, actualism remains a widely held and influential position in contemporary analytic philosophy, particularly among those who are suspicious of non-actual entities or of the metaphysical extravagance of full-blooded modal realism. It provides a framework for understanding possibility, necessity, and counterfactuals while insisting that all that exists—concrete or abstract—is, in the strictest sense, actual.