Bertrand Russell once received a letter from logician Christine Ladd-Franklin declaring herself a solipsist and expressing surprise that there were no others. That unintentional punchline opens an exploration of solipsism, the position that only your own mind is certain to exist. Starting with Descartes’ project of radical doubt and the three presuppositions that fuel solipsistic thought, the episode lays out the three flavors of the idea: metaphysical, epistemological, and methodological solipsism, and why the last is treated as a stress test for reality rather than a belief system.

From there the discussion moves through materialism versus idealism, Berkeley’s claim that to be is to be perceived, the egocentric predicament, Leibniz’s identity of indiscernibles, and the philosophical zombie. It then turns East to Advaita Vedanta, the Yoga Vasistha’s refutation of personal solipsism, the Yogacara mind-only school, Ratnakirti’s treatise on other minds, and the Buddhist concept of dependent arising. Modern angles include Karl Popper on falsifiability, David Deutsch’s use of Occam’s razor, Caspar Hare’s egocentric presentism, and Christian List on the logical contradictions of first-person perspective. The episode closes with the developmental psychology suggestion that infants begin life in a state of literal solipsism.

• Descartes’ radical doubt, the cogito, and the three core presuppositions behind solipsistic thought
• Metaphysical, epistemological, and methodological solipsism, and why one host calls the methodological version a philosophical cop-out
• Berkeley’s idealism, the egocentric predicament, and how radical solipsism would make your unconscious the author of every book and symphony
• Eastern responses: Advaita Vedanta’s non-duality, the Yoga Vasistha’s objection that reality resists your will, and dependent arising as a middle path
• Popper’s falsifiability, Deutsch’s Occam’s razor, egocentric presentism, and why Schopenhauer and Gardner said a practicing solipsist belongs in a madhouse