Part One: Taking rationalism seriously

In the Cells of the Eggplant aims to level up rationality. As a first step, we need to understand how and when and why rationality works. Rationalism is a theory about that. “Taking it seriously” implies investigating whether the theory is correct. We’ll find it isn’t.

We need a better understanding of rationality. Fortunately, one is available, and Part Three of The Eggplant explains it. So why not just start there?

Rationalism is the familiar, taken-for-granted understanding of rationality, accepted without much thought by most technical professionals. You learned it—largely by osmosis—in high school science classes. It’s simple and it makes sense. It’s a good-enough explanation of how you solved assigned coursework problems as an undergraduate. It’s uncommon to notice it’s not a good description of your experience of using rationality on the job, in the real world, after leaving school.

The Eggplant’s explanation of rationality is quite different, not just in content, but in “feel.” It relies on concepts you may not have encountered before, and that may seem strange or even repellent at first. If you jumped straight into Part Three, you might find its explanations alien, implausible, and complex in comparison with rationalism. The natural reaction: “this is weird nonsense; why not just rationalism?”

“Why not just rationalism” is half the agenda of Part One. Until one accepts that rationalism faces serious unresolved problems, not just as a philosophical theory but as a guide to practice, it’s difficult to take any alternative seriously.

Happily, it turns out that the specific ways rationalism is wrong point straight at a better understanding. That’s the other half of the agenda: causal diagnosis of rationalism’s many failure modes. That guides the construction of the alternative.

A pattern emerges: the overall reason rationalism can’t work. Every rationalist theory gets wrecked, in stormy seas of counterexamples, on the black reef of nebulosity.

This implies that the relationship between crisp rational systems and nebulous reality is key to understanding how and when and why rationality works. That leads naturally to the quite different understanding in Part Three.

The structure of Part One

The first three chapters of Part One are preliminary. They provide definitions of the subject matter, and introduce needed concepts. They also explain what sort of explanation The Eggplant aims for. It is not cognitive science, philosophy, or history. It is practical, not theoretical—although it often has to address theories, to dispel misconceptions that are misleading for practice.

Most of Part One works through a series of increasingly sophisticated, standard rationalist models that try to explain what it means to believe a true fact. That is a fundamental question for rationalism.

The aim here is not to conclusively refute these theories—because it is uncontroversial that each does fail. Rather, we will examine each in enough detail to find its root problem. Then it becomes plausible that no similar model can work. That suggests we need some quite different story.

Part One poses a potential danger. For many skilled in the use of technical rationality, rationalism is an important part of personal identity. Coming to understand how it is mistaken and sometimes harmful can be emotionally devastating. “Bypassing post-rationalist nihilism,” at the end of Part One, explains how to avoid that shock. If the first twinges of doubt in rationalism induce vertigo, it may be good to skip ahead to read that.


This page introduces a section containing the following pages:

  • Rationality, rationalism, and alternatives

    Defining the subject matter: rationality, rationalism, reasonableness, and meta-rationality.

  • Rationalism’s responses to trouble

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

  • Positive and logical

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

  • 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.

  • 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.

  • The value of meaninglessness

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

  • The truth of the matter

    Formal rationality requires absolute truths, but those are rare in the eggplant-sized world. How do we do rationality without them?

  • Reductio ad reductionem

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

  • Are eggplants fruits?

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

  • 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.

  • 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.

  • 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.

  • The National Omelet Registry

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

  • Objects, objectively

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

  • 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.

  • 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.

  • Where did you get that idea in the first place?

    Rationalism does not explain where hypotheses, theories, discoveries, inventions, or other new ideas come from.

  • The Spanish Inquisition

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

  • Probabilism

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

  • Leaving the casino

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

  • What probability can’t do

    If probability theory were an epistemology, we’d want it to tell us how confident to be in our beliefs. Unfortunately, it can’t do that.

  • The probability of green cheese

    A thought experiment shows why probability theory and statistics cannot address uncertainty in general.

  • Statistics and the replication crisis

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

  • Acting on the truth

    Rationalist theories of action try to deduce optimal choices from true beliefs. This is rarely possible in practice.

  • ⚒︎ Overcoming post-rationalist nihilism

    Realizing rationalism is wrong can be devastating. Antidotes to the ensuing rage, anxiety, and depression are available, fortunately!

This page is in the section In the Cells of the Eggplant.

The previous page is Meta-rationality: An introduction. (That page introduces its own subsection.)

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