modal realism

philosophy

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July 17, 2026

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Modal realism is a philosophical view asserting the existence of numerous "possible worlds" beyond our own actual world. These worlds are considered distinct, spatiotemporally closed systems, each containing its own unique set of concrete particulars with their properties and relations. This concept is closely tied to modal logic, which deals with notions of necessity and possibility. In modal logic, a proposition is considered necessarily true if it holds in all possible worlds, and possibly true if it holds in at least one possible world. Philosopher David Lewis is a prominent defender of this uncompromising form of modal realism. However, this view faces epistemological challenges, leading to alternative theories like moderate realism or fictionalism, which aim to utilize possible-world semantics without fully committing to the existence of these other worlds.12

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multiverse
Types of multiverses
This idea, known as modal realism, has been developed in philosophy, notably by the American David Kellogg Lewis in the 1970s and ’80s. In physics and mathematics, meanwhile, it has been hypothesized (particularly in the 1990s by Swedish American physicist Max Tegmark and German computer scientist Jürgen Schmidhuber)
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This idea, known as modal realism, has been developed in philosophy, notably by the American David Kellogg Lewis in the 1970s and ’80s. In physics and mathematics, meanwhile, it has been hypothesized (particularly in the 1990s by Swedish American physicist Max Tegmark and German computer scientist Jürgen Schmidhuber)
Read More

realism
Possible worlds
One kind of modal realism holds that there is a distinctive class of truths essentially involving the modal notions of necessity and possibility. Since the mid-20th century, however, advances in modal logic—in particular the development of possible-world semantics—have given rise to a further, distinctively ontological dispute concerning whether…
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One kind of modal realism holds that there is a distinctive class of truths essentially involving the modal notions of necessity and possibility. Since the mid-20th century, however, advances in modal logic—in particular the development of possible-world semantics—have given rise to a further, distinctively ontological dispute concerning whether…
Read More