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A credibility revolution in the post-truth era

Acting on the truth

The truth of the matter

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Rationality and refrigerators

This book offers more sophisticated understanding of truth than both rationalist absolutism and postmodernist relativism.

Reasonable believings

The epistemological categories—truth, belief, inference—are richer, more complex, diverse, and nebulous than rationalism supposes.

Reference: rationalism’s reality problem

The correspondence theory of truth doesn’t work by metaphysical magic. We must do the work to make it work—by any means necessary.

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Maps, the territory, and meta-rationality

“The map is not the territory”—what is it then? How do rational models actually work?

When will you go bald?

“Shades of gray” is sometimes a good way to think about nebulosity—the world’s inherent fuzziness—but not always.

The value of meaninglessness

Recognizing that some statements are neither true nor false was a major advance in early 20th-century rationalism.

Interlude: Ontological remodeling

Reconfiguring categories, properties, and relationships is a meta-rational skill—key in scientific revolutions.

Reductio ad reductionem

Reduction is a powertool of rationality, but reductionism can’t work as a general theory; most rationality is not reduction.

Upgrade your cargo cult for the win

Richard Feynman derided “cargo cult science” that sticks to fixed systems. Innovation requires an upgrade to fluid, meta-systematic inquiry.

Rationalism’s responses to trouble

Rationalism responds to its failures, in the face of nebulosity, by making more complicated formal theories.

The parable of the pebbles

Even counting, the simplest rational method, works only with the aid of non-rational support.

Overdriving approximation

Approximation is a powerful technique, but is not applicable in all rational work, and so is not a good general theory of nebulosity.

The National Omelet Registry

Rationalism implicitly or explicitly assumes that every object in the universe has a unique ID number.

Judging whether a system applies

Rationality requires judging whether a system of reasoning applies to a situation—but that judgement cannot be systematic!

Depends upon what the meaning of the word “is” is

Formal logic successfully addresses important defects in traditional, Aristotelian logic, but cannot deal with contextuality.

Probability theory does not extend logic

Probability theory is sometimes called a complete theory of rationality, on the mistaken belief it generalizes logic. I explain why this is wrong.

Objects, objectively

Rational methods assume objects are objectively separable; but they aren’t. How do we use rationality effectively anyway?

This is not cognitive science

The Eggplant is neither cognitive nor science, although it seeks a better understanding of some phenomena cognitive science has studied.

What they don’t teach you at STEM school

The syllabus for a curriculum teaching meta-rational skills: how to evaluate, combine, modify, discover, and create effective systems.

Ignorant, irrelevant, and inscrutable

Distinguishing irrational, anti-rational, and meta-rational critiques of rationalism helps reply effectively.

Are eggplants fruits?

Formal methods formally require impossibly precise definitions of terms. How do we use them effectively without that?

What can you believe?

Propositions are whatever sort of thing it is you can believe. Nothing can play that role; so we need a different understanding of belief.

Is this an eggplant which I see before me?

Rationalist theories assume perception delivers an objective description of the world to rationality. It can’t, and doesn’t try to.

Statistics and the replication crisis

The mistaken belief that statistical methods can tell you what to believe drove the science replication crisis.

You are accountable for reasonableness

Accountability is the key concept in understanding mere reasonableness, as contrasted with systematic rationality.

The purpose of meaning

Peculiar features of language make sense as tools to enable collaboration, rather than to express objective truths.

How To Think Real Good

Practical epistemology: heuristics for how to think about difficult things, particularly using formal methods.

A bridge to meta-rationality vs. civilizational collapse

A bridge from systematic rationality to fluid meta-rational understanding may be necessary to prevent civilizational collapse.

The world is everything that is the case

Aristotelian logic was mistaken both in details and overall conception, yet its key ideas survive in contemporary rationalism.

Nutrition: the Emperor has no clothes

Nutrition science has conclusively failed; it was myths invented to satisfy compulsive hunger for meaning. Now what?

Positive and logical

Early 20th-century logical positivism was the last serious rationalism. Better understandings of rationality learn from its mistakes.


Probability theory seems an attractive foundation for rationalism—but it is not up to the job.

Aspects of reasonableness

A summary explanation of everyday reasonable activity, with a tabular guide and a concrete example.

How we refer

We accomplish reference by any means necessary: observable, improvised work that makes it clear what we are talking about in context.

Reasonable ontology

Reasonableness works with nebulous, tacit, interactive, accountable, purposeful ontologies, which enable everyday routine activity.

Part Three: Taking rationality seriously

A pragmatic understanding of how systematic rationality works in practice can help you level up your technical work.

The Spanish Inquisition

Unboundedly many issues may be relevant to any practical problem, so mathematical logic does not work as advertised.

Leaving the casino

Probabilistic rationalism encourages you to view the whole world as a gigantic casino—but mostly it is not like that.

Comments with a matching subject

Categories and Truth by David Chapman at Nov. 4, 2017, 3:59 p.m.

One object, one truth by David Chapman at July 1, 2020, 11:37 a.m.

Comments with matching text

The meta-rationalist sneer and objectivity by fot at April 30, 2019, 3:22 a.m.

The irony of Meaningness hastening civilisational collapse by shane at July 18, 2020, 2:12 a.m.

Staying quiet in the boat is hard by Marybeth Lambe at Oct. 29, 2017, 8:31 p.m.

Chaitin, the post-rationalist by David Chapman at May 16, 2016, 8:05 p.m.

Ha! by Kenny at Sept. 1, 2020, 10:30 a.m.

Shifting target and meta-certainty by David Chapman at July 19, 2013, 2:37 p.m.

Reality? by Katherine at May 2, 2016, 6:14 p.m.

Selfish reasons by Duckland at May 17, 2016, 4:05 p.m.

What isn't delivered? by David Chapman at Dec. 14, 2016, 11:41 a.m.

That was fun - thanks for by Joshua Brule at April 18, 2017, 8:03 p.m.

A few issues by DickHurts at Oct. 8, 2020, 7:49 a.m.

The core of LW Bayesianism by Kaj Sotala at July 20, 2013, 2:45 a.m.

Learn logic and set theory up to Cohen forcing. by Lawrence D'Anna at May 2, 2016, 10:37 a.m.

Stage 5 Training by Alleged Wisdom at May 2, 2016, 9:42 p.m.

The inseparable nebulosity and pattern of mathematics by David Chapman at May 4, 2016, 8:21 a.m.

Taoism and nebulosity by Y.K. Goon at Feb. 15, 2017, 7:01 p.m.

I think another thing I've by Peter at July 25, 2017, 7:52 a.m.

Existence isn't any-'thing' by Bird Handorbush at Nov. 30, 2017, 11:18 p.m.

This Is The Best Portrait Of "The AI Mangle" I've Ever Read by JenniferRM at July 10, 2018, 1:52 a.m.

LW's definition of Bayesianism by Kaj Sotala at July 19, 2013, 2:27 a.m.

Agreements and disagreements by David Chapman at Aug. 12, 2013, 10:15 a.m.

real-world v's abstract reasoning by Tom Campbell-Ricketts at Aug. 21, 2013, 10:12 a.m.

Newsflash: there are no gods! by tom campbell-ricketts at Aug. 22, 2013, 12:26 p.m.

Rapture of the nerds; Ainslie's cure for rationalism by mtraven at Aug. 24, 2013, 10:10 a.m.

Not quite sure we are speaking the same language by Tom Campbell-Ricketts at Aug. 26, 2013, 1:20 p.m.

Maybe logic will help by David Chapman at Aug. 26, 2013, 6:04 p.m.

Mathematical Platonism by Dan at May 18, 2016, 4:27 p.m.

Haack and Peirce by Dan at May 22, 2016, 3:31 p.m.

I didn't know that lesswrong by anders horn at June 7, 2016, 8:16 p.m.

“Pop Bayesianism” is a by Kaj Sotala at June 19, 2016, 4:43 a.m.

Is it a strawman? by David Chapman at June 20, 2016, 1:29 p.m.

5 more reasons why GW wasn't President by Malcolm Ocean at June 28, 2016, 12:52 a.m.

27 modes of reasoning are enough for AGI by mjgeddes at July 30, 2016, 9:40 p.m.

what exactly is required that by Romeo Stevens at Dec. 14, 2016, 2:12 p.m.

Thanks for answering by John Nerst at Dec. 15, 2016, 1:20 a.m.

Definite answers by David Chapman at Dec. 15, 2016, 2:42 p.m.

Beyond rationalism by Mimetic Arbitrage at July 24, 2017, 6:43 a.m.

Uncertainty vs. fuzziness vs. illegibility vs. nebulosity vs... by Josh Brule at Oct. 30, 2017, 1:32 p.m.

Reasonableness and random thoughts by Dan at Oct. 30, 2017, 3:21 p.m.

Heidegger, AI, and rationality by Mikael Brockman at Oct. 31, 2017, 2:53 p.m.

Jam tomorrow, but never jam today by Richard Kennaway at Nov. 7, 2017, 7:55 a.m.

Modal & Non-Monotonic Logics by mjgeddes at Nov. 8, 2017, 5:36 p.m.

Clarifying the two cultures by nostalgebraist at July 12, 2018, 9:09 a.m.

Looks more effective != is more effective by Anonymous Coward at July 16, 2018, 4:58 p.m.

On "ratholes" by James at Jan. 28, 2020, 11:40 p.m.

Stopping points vs origins by Peter Corbett at Feb. 21, 2020, 4:51 a.m.

water in the eggplant by Ed Giniger at July 3, 2020, 7:10 a.m.

The stuff of reference by Julia at Sept. 7, 2020, 6:26 a.m.

Yudkowsky and the mythical OTR by Daniel at Nov. 13, 2021, 11:09 a.m.

My explanation by Dave Kunard at Nov. 21, 2021, 10:37 a.m.

Lectures on the History of Philosophy, Volume 3, p. 550 by David Chapman at April 14, 2023, 12:13 p.m.