Modal Realism

Modal Realism (Concepts & Beliefs)

Welcome to a fascinating journey into the realm of modal realism, a thought-provoking metaphysical theory that delves into the existence of possible worlds and their relationship to our own. At the core of this theory is the notion that all possible worlds are just as real as our actual world. Let’s dive deeper into this concept and explore the key ideas and arguments put forth by philosopher David Lewis.

Key Takeaways:

  • Modal realism, a metaphysical theory, posits that all possible worlds are equally real.
  • David Lewis, the proponent of this theory, argues that possible worlds are irreducible entities, existing alongside our own.
  • Possible worlds have modal properties and counterparts, which exist in different possible worlds.
  • Modal realism offers an explanatory account for modal properties and enhances our understanding of necessity and possibility.
  • Critics raise concerns about the theory’s inflated ontology and the equal treatment of possible and actual objects.

The Main Tenets of Modal Realism

Modal realism, the philosophical theory put forth by David Lewis, is grounded in several fundamental doctrines regarding possible worlds. These tenets provide the foundation for understanding the nature of possible worlds and their relation to the actual world.

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  1. Possible worlds exist: According to Lewis, possible worlds are not hypothetical constructs but are just as real as our own world. They are not mere figments of imagination, but ontologically genuine entities.
  2. Same sort of things: Possible worlds are of the same nature as our actual world. They are not fundamentally different; instead, they vary in their content and the arrangement of their elements.
  3. Irreducible entities: Possible worlds, as conceived by Lewis, are irreducible entities. They cannot be broken down into simpler components or explained away by appealing to other concepts or entities.
  4. Indexicality of “actual”: The term “actual” is indexical, meaning that it refers to the world in which the speaker is situated. It is relative to the perspective of the individual, rather than an absolute designation.
  5. Spatiotemporal interrelations: Possible worlds are unified through the spatiotemporal interrelations of their constituent parts. Just as objects and events in our world have spatial and temporal relationships, so do the elements within possible worlds.
  6. Causal isolation: Each possible world is causally isolated from every other world. This means that events and phenomena within one world do not have any causal impact on other worlds. Causal connections are confined within the boundaries of each individual world.

These six main tenets form the core principles of modal realism. They provide a framework for understanding the existence and characteristics of possible worlds and illuminate the ontological relationships between these worlds and our own actual world.

Illustration of Modal Realism

To further understand the main tenets of modal realism, consider an illustration that demonstrates the relations between different possible worlds:

Possible Worlds Content
Possible World 1 Same physical laws as our actual world, but different historical events.
Possible World 2 Same historical events as our actual world, but different physical laws.
Possible World 3 Different physical laws and historical events compared to our actual world.

In this illustration, the table showcases three possible worlds and their respective content. Each world diverges from our actual world in terms of physical laws and/or historical events. It exemplifies how possible worlds can differ in content while sharing the same ontological status as our actual world.

Arguments for Modal Realism

Lewis provides several reasons for accepting modal realism. He argues that modal realism is theoretically useful for modal reasoning and helps us make sense of commonly accepted expressions in natural language that seem to imply ontological commitments to possible worlds. According to Lewis, the best theories are those that are explanatory, and modal realism provides an explanatory account for modal properties.

One commonly cited argument for modal realism is the argument from ways. This argument states that if there are statements about how things could have been, then there must be other possible worlds where those statements are true. By accepting modal realism, we can account for the truth of such statements and their relation to possible worlds.

Modal realism also has theoretical usefulness. It allows us to reason about modal concepts and properties in a systematic way, providing a framework for understanding necessity and possibility. By positing the reality of possible worlds, modal realism enables us to explore the theoretical implications of modal metaphysics and advance our understanding of modal philosophy.

Furthermore, modal realism provides an explanatory account for natural language expressions that involve modal concepts. It offers a way to interpret and understand statements like “It could have been otherwise” or “There might have been a different outcome.” Modal realism allows us to analyze these expressions in terms of possible worlds and modal properties, providing a clearer understanding of their meaning.

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While modal realism has its critics who argue against its consequences and ontology, the reasons given by Lewis, such as its theoretical usefulness and ability to account for natural language expressions, provide a strong basis for considering modal realism as a valid metaphysical theory.

Criticisms of Modal Realism

Critics of modal realism raise several objections to the theory. One major objection is that it leads to an inflated ontology, positing the existence of an infinite number of possible worlds and entities. This runs counter to Occam’s razor, which states that entities should not be multiplied without necessity.

Additionally, critics argue that it is counterintuitive to treat possible objects the same ontologically as actual objects. This line of thought is further developed in the argument from morality, which shows that treating actual and non-actual persons equally would lead to highly implausible consequences for morality, such as the moral principle that every choice is equally permissible.


Modal realism, as proposed by David Lewis, presents a captivating theory on the existence of possible worlds and their relationship with the actual world. While it has sparked philosophical debates and encountered criticism, modal realism offers a comprehensive framework for comprehending modal properties, necessity, and possibility. By asserting the actuality of possible worlds, Lewis’s theory paves the way for new avenues of exploration in metaphysics and modal philosophy.

Despite the objections raised against it, modal realism continues to hold significance and exert influence in contemporary philosophy. It provides a thought-provoking perspective on the nature of reality and expands our understanding of the possibilities that exist beyond our immediate experience. The philosophical implications of modal realism prompt profound inquiries into the nature of truth, the limits of ontology, and the fundamental nature of existence itself.

Modal realism’s comprehensive account of possible worlds challenges conventional notions and invites us to reconsider our presuppositions. Its exploration of modal metaphysics offers a rich and nuanced perspective on alternative realities and their relationship to our own. While modal realism has its detractors, its enduring impact on contemporary philosophy cannot be denied.


What is modal realism?

Modal realism is a metaphysical theory proposed by philosopher David Lewis that posits the existence of multiple possible worlds that are just as real as the actual world.

How does modal realism view possible worlds?

Modal realism holds that possible worlds are not fundamentally different from the actual world but differ in content. Lewis argues that they are irreducible entities in their own right.

What is the role of the term “actual” in modal realism?

According to Lewis, the term “actual” is indexical, meaning that it refers to the world in which the speaker exists.

How are possible worlds related to each other in modal realism?

In modal realism, possible worlds are spatiotemporally isolated from each other and causally isolated. They are unified by the spatiotemporal interrelations of their parts.

Why does modal realism argue for the existence of possible worlds?

Lewis offers several reasons, including the theoretical usefulness of modal reasoning and the explanatory power of modal realism for understanding modal properties. The argument from ways suggests that if statements about how things could have been are true, then there must be other possible worlds where those statements are true.

What criticisms have been raised against modal realism?

Critics argue that modal realism leads to an inflated ontology by positing the existence of an infinite number of possible worlds and entities. They also find it counterintuitive to treat possible objects and actual objects with the same ontological status. The argument from morality highlights the implausible consequences of equal treatment for actual and non-actual persons in moral decision-making.

What are the philosophical implications of modal realism?

Modal realism raises important questions about the nature of possibility and necessity, and it provides a comprehensive framework for understanding modal properties. Despite objections, modal realism remains a significant and influential concept in contemporary philosophy.

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