Bayesian Rationality

"What do you think you know, and how do you think you know it?"
-The fundamental question of Rationality

What is it?

Rationality (more precisely "Bayesian Rationality") is a community, philosophy, and epistemology.
  • As a community, its nexus is the website 'Less Wrong', and has various physical meetups across the world, ranging from coffee shop hangouts to large organizations.
    • Some notable names in the movement are Eliezer Yudkowsky (a prominent AI researcher, author of 'Harry Potter and the Methods of Rationality', and founder of the community), Scott Alexander (psychiatrist, author, and founder of the Slate Star Codex/Astral Codex Ten blog), Julia Galef (author, co-founder of the Center for Applied Rationality), and Robin Hanson (professor of economics, founder of the blog where Yudkowsky began his writings)
  • As a philosophy, it concerns itself with knowing true things so you can accomplish one's goals most effectively (or, as the community affectionately says, "winning").
    • This sounds simpler than it is. It includes understanding one's goals at a deep enough level that you do not actively work against yourself as people often do. It also requires learning how the world around you works well enough so you can influence it, which brings us to...
  • As an epistemology, it exists with the Foundherentist framework, where Bayesian Reasoning, Methodological Naturalism, and Skeptical Empiricism mutually cohere and correct each other, while serving as the foundations upon which all other beliefs are derived.
    • It assumes that there is an objective truth which exists regardless of what one believes, that this truth can be incrementally discovered via experimentation and reason (science, decision theory, General Semantics, and Bayesian probability theory chief among its methods), but that cognitive biases and other errors of thinking often get in the way (which can be mitigated or solved outright if one trains hard enough). This is especially critical because in order for beliefs to cohere properly, they must be as accurate as possible so they can incrementally update each other and provide a foundation for one's Map.

What does it teach?

Rationality is not a set of tenets of what to think, but a framework of how to think.
This is not an exhaustive list of everything, these are simply what I think are the foundational lessons. To learn more, visit

"The Map is Not the Territory"

  • Your beliefs are a way to navigate the world around you, like a map for navigating a territory.
  • Your beliefs (and your ignorance) are a fact about you, not a fact about reality; no more than a map of New York City is actually New York.
  • Because a map can never be the territory, all your beliefs should be held with a confidence level (ie you should think probabilistically); this is what allows you to keep your mind open to new evidence.

"Make Your Beliefs Pay Rent"

  • Every belief that is worth occupying your head should be able to make an advance, falsifiable prediction about reality. A belief that doesn't make predictions is wishful thinking at best, delusion at worst, and is not paying its rent. Evict it.
  • Take your ideas seriously enough to recognize what it would look like if you were wrong.

"Notice Your Confusion"

  • Confusion or surprise means that either your map of the world is wrong/incomplete, or the information you are receiving is wrong/incomplete.
    • This should be treated as a large STOP sign. Do not attempt to rationalize it away with an explanation. You cannot reliably resolve confusion about the world using the same combination of map and information that became confused. Seek more data.

"Politics is the Mind-Killer"

  • Your political/identity-based beliefs should always be held under extra scrutiny (keep your identity small!)
  • You can decry someone's actions, up to and including calling for the death penalty, while still acknowledging that they may have been doing what they thought was best. Nobody is the villain in their own story, and actual psychopathic monsters are exceedingly rare.
  • It is okay to be sad when bad things happen to people, even when they "deserved it". That person could have been your friend and a noble/intelligent human being if things had been different.

"Know How to Communicate"

  • Arguing over definitions is a pointless exercise if you already know what the other person means; if a word gets in the way of communication, it has defeated its one purpose. "Taboo" a word if you and your conversation partner are having difficulty with it, forcing you both to articulate what you really mean.
  • Clear communication is clear thinking. The same thing that prevents you from communicating to others prevents you from communicating to yourself.
  • Do your words serve any purpose besides getting a rousing applause? Learn from the likes of Orwell on how to use speech to seek truth instead of just Virtue Signalling.

Rationalist Values/Culture

  • We do not reject emotion or the value of subjective experiences. Spock is not a Rationalist.
  • Seek to become stronger in the art of Rationality every day. "Tsuyoku Naritai!"
  • We will hear out any evidence-based argument, no matter how inflammatory or controversial. However, if it is a bad argument, or if we think you are arguing in bad faith, we will be the first to call you out on it.

"If the box contains a diamond, I want to believe that the box contains a diamond. If the box does not contain a diamond, I want not to believe that the box contains a diamond. Let me not become attached to beliefs I may not want."
-The Litany of Tarski

"What is true is already so. Owning up to it doesn't make it worse. Not being open about it doesn't make it go away. And because it's true, it is what is there to be interacted with. Anything untrue isn't there to be lived. I can stand what is true, for I am already enduring it."
-The Litany of Gendlin

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