Meanings
- no pluralpreceded with theAn online community of individuals, centered around the forum LessWrong and the blog Slate Star Codex, who discuss philosophy, psychology, and futurism through the lens of Bayesianism and rationality.
Several of the key concepts that do the rounds in the Rationalsphere these days first arose on SL4 and the Extropians.
2019 June 13, Tom Chivers, The Rationalist's Guide to the Galaxy, Orion, →ISBN2 more examples
I know that Cummings is a fan, because he regularly quotes them. His blogroll includes links to LessWrong, Slate Star Codex and Eliezer Yudkowsky, three of the key parts of the Rationalsphere.
2019 August 30, Tom Chivers, “Dominic Cummings is no chicken”, in UnHerdIn opposition to mainstream online culture, which believes that certain arguments should be off-limits, the rationalsphere wants to be able to talk about anything. Slate Star Codex — recently renamed Astral Codex Ten — the most prominent rationalist blog, has caused controversy by countenancing free-flowing discussion of topics such as race science and female harassment of men.
2021 April 13, Benjamin Wallace, “The Tech Elite’s Favorite Pop Intellectual Julia Galef on bringing the rationalist movement to the mainstream.”, in New York Magazine
Origin
rational + or rationalist + -sphere (“designating a particular realm or interest of a group of people, object, etc”)
Full word history & related roots →Cite this entry
rationalsphere. (n.d.). In WatkinsX Dictionary. Retrieved November 3, 2026, from https://dictionary.watkinsx.com/word/rationalsphere
“rationalsphere.” WatkinsX Dictionary, https://dictionary.watkinsx.com/word/rationalsphere. Accessed November 3, 2026.
WatkinsX Dictionary, s.v. “rationalsphere,” accessed November 3, 2026, https://dictionary.watkinsx.com/word/rationalsphere.
Source: rationalsphere on Wiktionary, CC BY-SA 4.0.