The hope that systematic rationality can reliably provide certainty, understanding, and control fails when it encounters nebulosity.

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.