The rationalist movement, rationality community,1 rationalsphere or rationalistsphere2 represents a set of modes of bayesian thinking from self-described rationalists or 'aspiring rationalists' typically associated with the Less Wrong diaspora and their associated communities.

This page was last properly edited in December 2017, around the time LW2.0 was getting started. It may not accurate reflect the state of affairs today – either culture or how the community sees itself. – Ruby


Following the wind-down of the first era of Less Wrong in 2014, triggered primarily via the departure of Eliezer Yudkowsky and other top writers, the formerly closer-knit on and offline groups continue with a lessened central focus.

Arguably, Scott Alexander has emerged as the most influential remaining figurehead and Slate Star Codex commands the highest single point of engagement within the restructured community.

In 2016-2017, discussion of revival occurred and Vaniver was made benevolent dictator for life. He in turn empowered Oliver Habryka to form a team and launch the LessWrong 2.0 project which runs the current site.


This is a fertile land and we will thrive. We will rule over all this land! And we will call it...this land!

A popular illustration of the communities comprising and related to the movement was created in 2014 on Slate Star Codex34 (above).

A 2017 conceptual Venn diagram of the 'rationalsphere' has also been created.5


Scott Alexander has also suggested the following definition in 2016:6

The rationalist community is a group of people (of which I’m a part) who met reading the site Less Wrong and who tend to hang out together online, sometimes hang out together in real life, and tend to befriend each other, work with each other, date each other, and generally move in the same social circles. Some people7 call it a cult, but that’s more a sign of some people having lost vocabulary for anything between “totally atomized individuals” and “outright cult” than any particular cultishness.

But people keep asking me what exactly the rationalist community is. Like, what is the thing they believe that makes them rationalists? It can’t just be about being rational, because loads of people are interested in that and most of them aren’t part of the community. And it can’t just be about transhumanism because there are a lot of transhumanists who aren’t rationalists, and lots of rationalists who aren’t transhumanists. And it can’t just be about Bayesianism, because pretty much everyone, rationalist or otherwise, agrees that is a kind of statistics that is useful for some things but not others. So what, exactly, is it?

This question has always bothered me, but now after thinking about it a lot I finally have a clear answer: rationalism is the belief that Eliezer Yudkowsky is the rightful caliph.

No! Sorry! I think “the rationalist community” is a tribe much like the Sunni or Shia that started off with some pre-existing differences, found a rallying flag, and then developed a culture.

Other definitions include:8

...typical rationalist philosophical positions include reductionism, materialism, moral non-realism, utilitarianism, anti-deathism and transhumanism. Rationalists across all three groups tend to have high opinions of the Sequences and Slate Star Codex and cite both in arguments; rationalist discourse norms were shaped by How To Actually Change Your Mind and 37 Ways Words Can Be Wrong, among others.


...a community that call themselves Rationalists, that read ‘high-IQ sites’ such as Marginal Revolution, Less Wrong, and Slate Star Codex, and according to various surveys, identify as liberal, are atheist or agnostic, and, in general, hold a ‘realist’ philosophical worldview.

Additional attributes

A crowdsourced list of traits of community:10

Individualistic vs Organizational

It's a sphere!


Raemon argues the rationalist movement could be subdivided into individualistic and organisational views.11 Project Hufflepuff attempts to strengthen both approaches.

The Rationalsphere

Contains key modes of thinking for the individual including:

  • Truthseeking - biases, empiricism etc
  • Impact - making the world a better place ( e.g. effective altruism, AI safety )
  • Human - becoming a better person

On the other hand:

The Rationality Community

Encompasses the major subscribing organisations ( CFAR, Giving What We Can etc ) as well as the many meetup groups , friends and relationships discovered from participation in the community.


Adjacent ideas include:12

There are people who agree on few to no rationalist positions but still like going to our parties and reading our blog posts. I coined the term “rationalist-adjacent” for this group before I got the idea that the names of all subdivisions of the rationalist community should begin with the letter C...A lot of Less Wrong references a lot of nerd culture, such as catgirls, anime, fanfiction, Harry Potter, My Little Pony, etc

Skepticism of term

There is a some drive to avoid any 'isms' and instead focus on 'rationality' rather than 'rationalism.23


The culture is often defined by its saying such as those featured in

See also


  1. Economics, stale memes, and distraction from productive activity
  2. There doesn't appear to be clearly preferred term - August 2017
  4. Created with Photoshop and Fractal Mapper. Uses a lot of free clipart. Relevant tutorials at the Cartographers Guild forums.
  11. What exactly is the "Rationality Community?"
  22. Note on Terminology: "Rationality", not "Rationalism"