Introducing the central concepts

Cirrus clouds

Exactly how many clouds are in this photograph?
Image courtesy Dimitry B

These are the main concepts used in The Eggplant: nebulosity; rationality, reasonableness; rationalism; meta-rationality; metaphysics, ontology, and epistemology; vagueness and uncertainty.

This chapter defines these terms and also sketches the ways the concepts relate to each other. That gives, in effect, another introductory summary of some major themes of the book.


Literally, nebulosity means “cloud-like-ness”:

  • Boundaries: Clouds do not have sharp edges; they thin out gradually at the margin. As you approach a cloud (in an airplane, or on a mountain hike), you cannot say quite when you have entered it.
  • Identity: It may be impossible to say where one cloud ends and another begins; whether two bits of cloud are part of the same whole or not; or to count the number of clouds in a section of the sky.
  • Categories: Cirrocumulus shades into cirrus and into altocumulus; clouds of intermediate form cannot meaningfully be assigned to one or another.
  • Properties: Depending on temperature and density, clouds may be white, gray, blue, or irridescent. There are no specific dividing lines between these colors. Clouds have diverse, highly structured shapes, which cannot be precisely described. First, because the edges are indistinct; and second because the shape is so complex that a full description would be overwhelmingly gigantic even were it possible. Yet meteorologists find useful phrases like “ragged sheets,” “wavy filaments,” “bubbling protuberances,” or “castle-like turrets.”

Clouds are an extreme case, but nebulosity is pervasive. Other than in mathematics and fundamental physics, nothing is ever definitely this-or-that. Everything is always somewhat this and somewhat that. Put under high enough magnification, a stainless steel ball exhibits the same indefiniteness as a cloud. No ball can be perfectly round, nor made of perfectly pure steel, nor can one definitely say whether some particular atoms are part of it or part of its surrounds.

For this reason, there are few if any absolute truths about the eggplant-sized world. Mostly, the best we can ever get is “true for all practical purposes.” And most of the truths we use, even in the hard sciences, are “pretty much true” or “true as far as a particular purpose goes.” This raises occasional problems for rationality in practice, and causes serious difficulties for rationalism as a theory. Meta-rationalism addresses these issues effectively.

Because of nebulosity, definitions can’t be perfectly precise. Some categories hang together only by “family resemblance”: there is no single common feature, it’s just that this is similar to that, which is similar to another thing.1 “Nebulosity” itself is, necessarily, a nebulous concept, which cannot be precisely defined.

However, it’s often useful to sharpen categories somewhat, and to disambiguate word meanings to some extent. Several of the key terms in The Eggplant—especially “rationality”—have previously been used in multiple ways, and clarity requires pointing out which I intend. The definitions in this chapter will still be somewhat vague. Meanings will come into better focus gradually, through understanding words’ use in later discussions.


Meanings of “rational” have evolved and proliferated over centuries. These share only a family resemblance, so no precise definition is possible. Various schools of thought have refined and promoted particular versions. Part One of The Eggplant explores some specifically.

I will treat rationality as a practical activity, things we actually do, rather than as a metaphysical ideal we should aspire to. Generally, rational methods are formal, systematic, explicit, technical, abstract, atypical, non-obvious ways of thinking and acting, which have some distinctive virtue relative to informal ones.2

“Systematic” and “formal” are key criteria, but both are nebulous. They are a matter of degree. Mathematical logic is extremely formal; a chemistry methods manual is quite formal; a corporate personnel policy is somewhat formal; a “Do Today” task checklist is only barely formal. “System” is used vaguely to mean almost anything complicated. I’ll use it a little more specifically, as meaning a set of rules that can be printed in a book, which a person can consciously follow, and the activities and mechanisms that result.

Rationality works mainly with general knowledge. Ideally, it aims for universal truths. Generally, knowledge of a specific object does not count as “rational” unless it applies to every other object in some class. The glory of Newton’s theory of gravity is that it is true uniformly everywhere in the universe, equally for an apple and an asteroid.3 In fact, we’ll see that formal systems cannot deal with particular physical objects at all—one reason rationality is inadequate by itself.


In everyday usage, “rational” has an informal meaning of “thinking and acting in ways that make sense and are likely to work.” In this sense, “rational” is synonymous with “sensible.” It means “not stupid, crazy, or meaningless.” Somewhat arbitrarily, I will call this reasonableness, and reserve “rationality” for systematic methods.4

Much of The Eggplant is about the relationship between these two. Understanding that is a prerequisite for meta-rationality. Rationalism misunderstands reasonableness as a primitive approximation to rationality. In fact, it has somewhat different—though overlapping—functions. “Mere” reasonableness addresses the nebulosity of the everyday world effectively, which formal rationality can’t. Meta-rationality combines resources from reasonableness and rationality, plus ones of its own, to understand and act effectively in circumstances the others cannot manage.

I’ll use irrational to mean failure or refusal to think well or act effectively when you should. It means “unreasonable” or “nonsensical,” or “stupid” or “crazy,” in the non-clinical sense of those words.

By this definition, irrationality is contrary to all three of reasonableness, rationality, and meta-rationality. I will not use it to mean “not systematically rational.”


I will use rationalism to mean any belief system extolling broad claims about the value of rationality, going beyond the evidence of common experience. In the plural, rationalisms are diverse belief systems of this sort.

The most influential rationalisms attempt universality across domains: they are meant to apply in all situations and task types. Others are more specific: particular notions of rationality that apply only in mathematics, science, law, management, or accounting. The Eggplant considers mainly universal rationalisms, or ones meant to apply broadly in technical fields.

Typically, rationalisms attempt to form rational theories of rationality. That is, they seek systematic, explicit, technical, abstract, non-obvious explanations for how and why rationality works. Ideally, they aim for definite proof of rationality’s universal efficacy.

Typically, rationalisms specify some ultimate criterion according to which thinking or acting could be judged to be correct or optimal. Typically, they say that thinking in accordance with the criterion reliably produces true beliefs. They may also claim rationality yields maximally effective action.

For rationalism, ideal rationality means conforming to the criterion. Rationalism is normative: everyone ought to think and act that way, as nearly as possible.

Under this definition, “rationalism” must go beyond “formal methods are often useful, hooray!” That is the common experience: for anyone who uses such methods, their value is obvious.5 I will use rationalist to mean someone who promotes rationalism—rather than someone who just finds methods of systematic rationality often useful in practice.

Let’s consider a variety of claims about rationality, roughly from weaker to stronger:

  1. It is better to be rational than irrational
  2. Systematic rationality often works, so you should use it when appropriate
  3. Rationality (whose definition is left vague) is always good
  4. Rationality is all there is to thinking and acting well; it is sufficient for all purposes, and there’s nothing else you need
  5. Rationality is defined by such-and-such a criterion; you should conform to it as nearly as you can
  6. Certain specified methods meet the rationality criterion, so you should use them whenever you can
  7. There’s a single master method of rationality, which guarantees an optimal result

I think claims 1 and 2 are correct: formal rationality is hugely valuable and you should use it often. I will not count this as “rationalism.” Not everyone agrees, though. Let’s say that anti-rationalism is any worked-out denial of either 1 or 2. Meta-rationalism is not anti-rationalism, since it affirms the value of rationality.

“Rationalism” might be defined as holding claim 4 (that rationality is always sufficient) or above. Meta-rationalism denies 4-7, so it is not rationalism.

Claim 3 is a diffuse attitude of alignment. If rationality means just “thinking and acting well,” then it is correct by definition. Also, claim 3 is importantly right if it’s just a rejection of anti-rationalism. On the other hand, a diffuse, incoherent rationalist faith is imparted implicitly in the science curriculum. There must be a correct way to think, some rationalists suggest, but we don’t know quite what it is; or they extol a vague principle like “the scientific method.” No one has been able to give a detailed, empirically adequate explanation of what “the scientific method” is, so advocating it is nearly vacuous.6

I think the stronger claims 4-7 are mistaken. Formal rationality is rarely if ever sufficient on its own in real-world situations; there’s no fixed criterion for rationality; nothing can be guaranteed by or about rationality in practice; and there is no method that is always rational to use.

Distinguishing weaker and stronger claims about rationality may help correct both rationalist and anti-rationalist errors. I suspect many anti-rationalists react to overstated rationalist claims, rightly rejecting them, but then mistakenly go on to deny that systematic rationality is often valuable. I suspect many rationalists rightly wish to defend rationality’s genuine value, but mistakenly go on to affirm implausibly strong claims as well. Rationality does have “distinctive virtues” (which we’ll return to in Part Three); but these are nebulous and cannot be guaranteed.

Rationalism is based on a fantasy of how we would like knowledge, action, and reality to work. It would be highly convenient if they did. In a world without nebulosity, in which objects and properties were perfectly crisp, rationality would be fully adequate. But we do not live in such a world. To the extent that rationality does work, it is largely because we have engineered our world to make it behave more nearly that way.

Non-rational, reasonable judgement is unreliable, sometimes uncomfortable, and leads to conflict when people get different answers. When they get stubborn about that, or when misjudgment leads to disaster, it’s easy to regard all “reasonableness” as simply irrational. The hope of rationalism is that some mechanical criterion or procedure could provide certainty, understanding, and control by eliminating non-rational factors. This is not possible, because rationality by itself can’t deal with the nebulous eggplant-sized world at all. Abstract, formal reasoning cannot reach into that realm; it requires reasonable activity as a bridge.

The problem with rationalism is not that it is false as an abstract philosophical theory. (Who cares?) The problem is that it is misleading in practice. It encourages you to overlook nebulosity, and the bridging function of reasonableness it requires; so you end up using rationality wrongly. This is not a minor or theoretical danger. The replication crisis has revealed that most supposed knowledge in many scientific fields, derived through misuse of rational methods, is false.

Part One of The Eggplant explains a series of specific technical difficulties rationalism encounters. Each failure mode has the same underlying cause: denial of nebulosity.7

Meta-rationality and meta-rationalism

Meta-rationality means figuring out how to apply rationality in a specific situation, and skill in doing so. It is a word I made up, to cover insights about the use of rationality gathered from many disparate fields. A few people have used the term “meta-rationality” with similar meanings before, in passing, but I don’t know of any previous detailed account.8

Rationality and meta-rationality are complementary activities. Meta-rationality is not an alternative to rationality. Neither can operate without the other; they walk hand-in-hand.

Meta-rationality is not in the business of finding true beliefs or optimal actions. That’s rationality’s job. On the other hand, getting good at meta-rationality will make you more effective at rationality, and therefore better at finding true beliefs and optimal actions.

Meta-rationality selects and adapts rational methods to circumstances, so it is meaningless without rationality. Conversely, you cannot apply rationality without making meta-rational choices. However, since meta-rationality is rarely taught explicitly, it’s common to use only the simplest, default meta-rational criteria. Those are meta-rational nonetheless: there is no universal rational method, so in any situation you have to choose one and figure out how to apply it.

Meta-rationality is not the application of formal rationality to itself (as one might suppose from its name). Applying rationality to itself is a rationalist program. We’ll see that, because of nebulosity, reasoning about how to apply rationality cannot be formally rational. (But it should not be irrational or anti-rational either!)

Meta-rationalism is an understanding of how and when and why reasonableness, rationality, and meta-rationality work. Whereas rationality and meta-rationality are different sorts of things, rationalism and meta-rationalism are the same sort of thing: explanations of effective thought and action. Meta-rationalism finds rationalism an inadequate account, and offers a complete replacement.9 So, perhaps confusingly, while rationality and meta-rationality are complementary activities, rationalism and meta-rationalism are incompatible explanations.

Once you recognize that denial of nebulosity is the deep structure underlying each of the difficulties rationalism encounters, the solution approach is obvious: accept nebulosity from the beginning, and work with it, instead of trying to ignore or eliminate it. As a practice, meta-rationality does just that. As a theory, meta-rationalism is a more accurate account of the sort of world we live in; and so it gives better advice than rationalism in cases in which nebulosity matters.

Metaphysics, ontology, and epistemology

If you find these terms from philosophy off-putting, you are in good company. The Eggplant isn’t a philosophical book, and I’ll use the words in non-philosophical ways.

I’ll use “metaphysics” exclusively as an insult. I use it to mean: fancy arguments about sorts of things that can’t exist, and questions that couldn’t have answers. Some philosophers insist that it is a serious topic, but if you check your local bookstore, you’ll find that in reality it’s mostly about holistic chakra-balancing aromatherapy.

Some central claims of rationalism are also strictly metaphysical, and I’ll insult them as such.

I use “ontological” as engineers do.10 Ontology is about how the world is. Some ontological questions are: “What things, of what sorts, are there? What properties and relationships do they have?” By an ontology, engineers mean a set of answers, usually relative only to a specific domain.

Rather than advocating a particular ontology, I will reply, over and over again, in different ways: “These questions have no definite answers, due to nebulosity.” Meta-rationality is concerned mainly with ontological questions, and gives nebulous—but useful—answers.

Epistemology is about knowing. The epistemological questions are: “What is knowledge? What is a belief? How can we get true beliefs and eliminate false ones?” Rationality is mainly concerned with these epistemological issues; it generally ignores ontological ones.

We can’t fully separate epistemology and ontology. The first part of this book shows how rationalism tries to do that, and so goes wrong. How things are partially determines how you can know them. Nebulosity is pervasive, so little could be known definitely, even if we had unlimited access to reality. Most facts about clouds and eggplants are not absolutely true, only true-enough, and so they cannot accurately be believed absolutely. Meta-rational epistemology takes this nebulosity of truth, knowledge, and belief into account.

An easy misunderstanding is to equate ontology = in the world = objective = intrinsic, and in parallel epistemology = in your head = subjective = arbitrary. But to know something is usually thought to require that it is true; and truth is supposed to be objective and in the world, not in your head. Meanwhile, color, an ontological matter, is not intrinsic; it depends on incoming lighting, and sometimes on the viewing angle. It is objective: reasonable people will usually agree about whether something is red, although there are borderline cases. Then reasonable people will agree that disagreement is reasonable, and not insist on an absolute truth. Color is also not a matter of arbitrary personal opinion or social conventions; nearly every culture agrees on redness, and it’s largely determined by retinal biology.

Ontology is often dependent on human purposes, however, and can even vary moment-by-moment depending on your current purpose. Whether or not there is water in the refrigerator depends on why you care. If you are looking for something to drink, an eggplant probably won’t do—but if you are in a bio lab and the small amount of water vapor continually emitted by an eggplant would ruin the sample you were thinking of storing in the refrigerator, a warning that there is water in the refrigerator could be important. These distinctions are not subjective or arbitrary or merely in your head. An eggplant is not a good way to slake thirst; and that is not a matter of opinion.

Explaining this properly would take a long diversion into philosophy, which is outside the scope of this book. (I’ll do that elsewhere in Meaningness.) As far as The Eggplant is concerned, it’s sufficient that ontology is about how the world is, setting aside abstract theoretical questions about what that means.

Vagueness, uncertainty, and nebulosity

The Eggplant considers three obstacles to rationality:11

Representational vagueness:
Inability to fix quite what a sentence, formula, or model means, and so how it relates to reality
Epistemological uncertainty:
Both “known unknowns”: whether a statement is true or false due to insufficient evidence; and “unknown unknowns”: relevant factors whose existence you are unaware of
Ontological nebulosity:
The fizzy, fuzzy, fluid indefiniteness of the world itself

These all have a similar flavor—they could all be covered by a word like “vagueness” or “fuzziness.” They all make it difficult to say that particular statements are definitely true or false. Ultimately, they are inseparable, and they are often confused in practice. However, the conceptual distinctions are helpful.

Rationalism mainly concerns itself with the first two obstacles. Those are about human cognition, so it may seem that rationality could overcome them. We can sharpen our language and gather more data, and then maybe eventually, or at least in principle, rationalism could deliver on its guarantee. Nebulosity is about the world, so it can’t be fixed.

Encountering representational vagueness, rationalism considers ordinary language defective, and tries to replace it with alternative, more formal systems. For instance, formal logic was designed partly as an antidote to linguistic ambiguity.

Sometimes sharper representations are valuable. The move to formalism is much of what gives rational methods their extraordinary power.

Fully eliminating vagueness turns out to be infeasible, however. And, the attempt is based on a fundamental misunderstanding of what ordinary language is for, and how it works. Ordinary language contains extensive resources for working with nebulosity. These get lost when you replace it with technical abstractions. Part Two, on reasonableness, explains some of them.

For meta-rationalism, ordinary language is not defective; it is well-suited to its actual purpose. Meta-rationality coordinates ordinary language’s nebulosity-clarifying methods with rational methods of formal notation.

Encountering uncertainty, rationalism asks “on what basis can we know whether this is true?” It assumes that well-formed statements are either absolutely true or absolutely false, that the problem of knowledge is to find out which, and that rationality is the solution. Of course, some things are true, and rational methods for determining truth can be highly effective in some situations.

Unfortunately, uncertainty can never be entirely eliminated, and formal reasoning methods don’t cope with it well. Probabilistic rationality handles some cases, but not all. “Unknown unknowns”—relevant factors you have not considered at all—can’t be incorporated into any formal system. Formal treatment of an uncertain fact requires specifying it in advance.

As we’ll see in Part Three, we can work effectively with unknown unknowns, but not in a formally rational framework.

Encountering ontological nebulosity, rationalism typically misinterprets it as either representational vagueness or epistemological uncertainty. Nebulosity negates any possibility of strong claims for rationality. It’s not a matter of ignorance, but of there being no definite, absolutely true answer to most questions. Perhaps, consciously or unconsciously, rationalism recognizes this, which is why it usually ignores or denies nebulosity.

Rationalism generally bases explicit denials of nebulosity on fundamental physics. There are two steps in the typical argument. Subatomic particles have absolutely definite properties, described by quantum field theory, which is absolute truth. (Let us grant this claim for the sake of the argument.12) The second step: everything is made out of particles, so everything is also absolutely definite. Thus, world is well-behaved, and there is an absolute truth to everything, even if we currently don’t know it. Quantum physics gives the correct ontology; that’s a solved problem.

This step doesn’t follow (as we’ll see later). Fundamental physics doesn’t have much to say about what I’ll call “the eggplant-sized world.” That extends from roughly the size of bacteria up—but size as such is not the issue. It is that the objects, categories, properties, and relationships we care about are not understandable in terms of fundamental physics.

In the eggplant-sized world, there are few if any absolute truths. Mostly the best we can get are “pretty much true” truths. No amount of additional information would resolve these into absolute ones.

“Gray areas” are the easiest way to think about nebulosity. Is it true that maroon is a shade of red? Well, pretty much, although it’s a bit of a gray area.

Such questions of degree do not exhaust nebulosity, though. Consider “yes, there is some water in the fridge: in the cells of the eggplant.” The problem here is not one of a gray area between water and non-water. Nor are we factually uncertain whether or not there is water in the fridge, so scientific investigation could answer the question. It is not that the word “water” has two different meanings, referring to two different kinds of water. It is that what counts as water depends on what you want it for.

Ontological questions depend on context and purpose. Contexts and purposes are endlessly variable. I’ll often use the term unenumerable to point to the practical impossibility of taking into account all factors that could potentially bear on specific situations. Useful truths must have practical implications for concrete problems. Universal, absolute truths cannot take into account unenumerable factors—and so mostly cannot be useful.

  • 1. The understanding of categories in terms of “family resemblance” originates with Ludwig Wittgenstein’s Philosophical Investigations.
  • 2. Some non-rational systematic religions and philosophies would also meet these criteria. There is a “demarcation problem” here. The usual meaning of “the demarcation problem” is to find criteria that clearly distinguish science from non-science. This seems to be impossible. Different sciences work quite differently, and have no single well-defined feature in common. However, the demarcation problems for both science and rationality are rarely an issue in practice. We know science and rationality when we see them, and can usually make a cogent argument for why a particular method or system is scientific or rational or not, even if there is no general rule.
  • 3. This applies to semi-formal rational systems as well. A company policy that said “employees must turn in their weekly timesheets by the following Thursday, except Bertrand” would not count as rational. In a rational policy, if Bertrand is an exception, it must be as an instance of a class. For example, if Bertrand is an exception because he’s on a secret solo dogsled expedition to the South Pole, a rational policy would be “employees must turn in their timesheets by the following Thursday, unless they are out of internet range, in which case they must turn it in by the Thursday following their return to civilization.”
  • 4. Although the concept is familiar to everyone, there seems to be no standard word for what I’m calling “reasonableness.” That is probably because it is usually viewed as a half-baked approximation to rationality, and therefore can be ignored. As we will see, this is inaccurate.
  • 5. In “Ignorant, irrelevant, and inscrutable,” I discuss irrationalists who simply don’t understand that formal methods are often useful, and anti-rationalists who oppose systematic rationality for aesthetic, political, religious, or “spiritual” reasons. Since the European Enlightenment, anti-rationalism has mainly been suppressed in favor of a consensus in favor of rationality among the powerful. There are ominous signs that this consensus may now be failing. See “A bridge to meta-rationality vs. civilizational collapse.”
  • 6. This is the demarcation problem again. It seems that any set of criteria for what counts as scientific winds up excluding some things that most scientists agree are science, and/or including some thing that aren’t. False positives typically include “pseudoscience,” meaning work that presents itself as science, and meets most or all typical criteria, but is clearly bogus. A famous case is Daryl Bem’s 2011 precognition paper. That satisfied the criteria for psychological experimentation at the time, but had to be nonsense. This sparked the replication crisis and the methods reform movement.
  • 7. In the language of Meaningness, this is a form of eternalism. Equivalently, it is the fixation of patterns as ontological absolutes. I mostly don’t use these terms in The Eggplant.
  • 8. The most extensive previous use of “metarationality” I’ve found is in Chapter 6 in Keith Stanovich’s Decision Making and Rationality in the Modern World. He uses the term to mean reflection on one’s preferences and on the consequences of choices in a decision-theoretic framework. This use is compatible with mine, although a narrower conception than mine, and not elaborated in much detail.
  • 9. Logically, there could be multiple meta-rationalisms: different theories about the relationships among reasonableness, rationality, and meta-rationality. Currently, there is not even one fully worked-out version, so meta-rationalisms in the plural are only hypothetical.
  • 10. The distinction between ontology and metaphysics in philosophy is nebulous. Some of the questions I describe as “ontological” might rather be called “metaphysical” by philosophers. On the other hand, ontology, as a branch of academic philosophy, examines many issues that I’d be inclined to lump with holistic chakra stuff.
  • 11. There are more obstacles to rationality than these three. For example, computational complexity theory puts practical limits on reasoning; this book doesn’t discuss that.
  • 12. There are two grounds for doubt: quantum indeterminacy, and physicists’ certainty that the existing quantum field theory is not correct. Nothing in The Eggplant relies on these doubts, however, so it simplifies the discussion to ignore them.


This page is in the section Introduction: Because rationality matters,
      which is in In the cells of the eggplant,
      which is in ⚒ Fluid understanding: meta-rationality,
      which is in ⚒ Sailing the seas of meaningness,
      which is in Meaningness and Time: past, present, future.

The next page in this section is The function and structure of the eggplant.

This page’s topic is Rationalism.

General explanation: Meaningness is a hypertext book (in progress), plus a “metablog” that comments on it. The book begins with an appetizer. Alternatively, you might like to look at its table of contents, or some other starting points. Classification of pages by topics supplements the book and metablog structures. Terms with dotted underlining (example: meaningness) show a definition if you click on them. Pages marked with ⚒ are still under construction. Copyright ©2010–2020 David Chapman. Some links are part of Amazon Affiliate Program.