Are other worlds as real as our own? David Lewis argued they certainly are.

Ideas & Philosophy · Published 3 October 2026 Swipe more like this →

In short: David Lewis, a towering figure in 20th-century philosophy, proposed that our universe is merely one of infinitely many equally real worlds. By treating possible worlds as concrete realities rather than abstract metaphors, he built a powerful framework to explain everything from causation and probability to the nature of language.

Born in 1941, David Kellogg Lewis spent most of his career at Princeton University, where he became one of the most influential systematic thinkers in modern philosophy. His work spanned logic, epistemology, and the philosophy of mind, but he is best remembered for his bold defense of 'modal realism.' While many philosophers use the language of possible worlds as a convenient shorthand, Lewis insisted that these worlds are as real as our own cosmos. He argued that every possible variation of history and every possible version of ourselves is realized somewhere in this vast, disconnected space of worlds.

This framework allowed Lewis to tackle complex metaphysical problems with striking clarity. He proposed that temporal relations are analogous to spatial ones; just as distant places are real despite being elsewhere, past and future events are real despite being elsewhere in time. He also developed the doctrine of 'Humean supervenience,' which posits that everything true about a world is determined by the distribution of local qualities—such as electric charge or temperature—across space and time. While he acknowledged that objective chance posed a challenge to this view, he spent years refining his position to account for the complexities of probability.

Beyond metaphysics, Lewis made foundational contributions to game theory and linguistics. In his 1969 book, 'Convention: A Philosophical Study,' he analyzed social conventions as solutions to coordination problems. He argued that conventions, like driving on the right side of the road, are self-sustaining behavioral regularities that emerge because they serve the interests of everyone involved. By applying these insights to language, he suggested that truth and trust are not inherent properties of sentences but are instead relational, established by the conventions of a population. His work remains a cornerstone of modern philosophical inquiry, celebrated for its technical rigor and breathtaking clarity.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?

Related

• Does the world exist when you look away, or is it all in your head?
• Is the world a container or the very act of appearing?
• Is the universe a personal creation or merely a series of physical accidents?
• Is the world you see real, or just a shared social agreement?
• A prominent theologian turned 9/11 conspiracy theorist, David Ray Griffin challenged modern academic materialism.
• Why does the feeling of being alive exist, and can science explain it?
• Did the Gospels record history, or did they craft a powerful, legendary myth?
• Is coming into existence a fundamental harm? A philosopher argues we should not procreate.
• Who was David the Invincible, the 6th-century philosopher shrouded in medieval legend?
• Dasein: Why Martin Heidegger believed human existence is a constant, urgent philosophical question
• How a mouse on a temple idol sparked a revolution in Indian religious thought
• Daniel Bensaïd: The French Marxist who challenged the boundaries of revolutionary strategy

More in Philosophers · More in Ideas & Philosophy · Latest · A–Z · All topics