Rationality: What It Is, Why It Seems Scarce, Why It Matters

by Steven Pinker

Man is a rational animal. So at least we have been told. Throughout a long life I have searched diligently for evidence in favor of this statement. So far, I have not had the good fortune to come across it.

The writing of Principia Mathematica evidently did not count as a wholly rational act.

The penultimate chapter will lay out how some of today’s florid outbursts of irrationality may be understood as the rational pursuit of goals other than an objective understanding of the world.

Though explanations of irrationality may absolve people of the charge of outright stupidity, to understand is not to forgive. Sometimes we can hold people to a higher standard. They can be taught to spot a deep problem across its superficial guises. They can be goaded into applying their best habits of thinking outside their comfort zones. And they can be inspired to set their sights higher than self-defeating or collectively destructive goals. These, too, are aspirations of the book.

Things that can’t go on forever don’t, and organisms can multiply only to the point where they deplete, foul, or saturate their environments, bending the exponential curve into an S.

A logistic curve.

the dividing line between science and pseudoscience is whether advocates of a hypothesis deliberately search for evidence that could falsify it and accept the hypothesis only if it survives.

It’s not that hard to see why.

Good place to introduce Bayes' Theorem.

The brightness of a patch on the retinal image depends not just on the pigmentation of the surface in the world but on the intensity of the illumination falling on it: a gray patch could have arisen from a black surface illuminated by a bright light or from a white surface illuminated by a dim one.

It also depends on the brightness of adjacent regions.

Instead of feeling any need to persuade, people who are certain they are correct can impose their beliefs by force. In theocracies and autocracies, authorities censor, imprison, exile, or burn those with the wrong opinions. In democracies the force is less brutish, but people still find means to impose a belief rather than argue for it.

it depends on how long you have to wait and how many marshmallows you get for waiting.

And whether you like marshmallows.

Donald Trump’s bluster in 2017 about using his bigger nuclear button to rain fire and fury on North Korea could charitably be interpreted as a revival of the theory.

Not to mention the GOP's constant debt limit crises and threats to make the US default on its debt.

As soon as we start insisting to others, “You must not hurt me, or let me starve, or let my children drown,” we cannot also maintain, “But I can hurt you, and let you starve, and let your children drown,” and hope they will take us seriously.

It is, however, a tenet of GOP policy.

When a rational argument slips into fallacy or sophistry, an even more rational argument exposes it.

Note to reviewers.

But the laws of logic are general-purpose: they apply whether the content is topical, obscure, or even nonsensical. It was this point, and not mere whimsy, that led Lewis Carroll to create the “sillygisms” in his 1896 Symbolic Logic textbook, many of which are still used in logic courses today.

My goodness! Somebody else who has read that book.

And the increasingly popular affective fallacy, in which a statement may be rejected if it is “hurtful” or “harmful” or may cause “discomfort.”

Media coverage thus drives people’s sense of frequency and risk: they think they are likelier to be killed by a tornado than by asthma, despite asthma being eighty times deadlier, presumably because tornadoes are more photogenic.

In large part the opposition is driven by memories of three accidents:

And the fact that a coal bomb is not a major component of anybody's defense strategy.

major contributor to post hoc probability fallacies is our failure to appreciate how many opportunities there are for coincidences to occur. When we are allowed to identify them post hoc, coincidences are not unlikely at all; they’re pretty much guaranteed to happen.

No testimony is sufficient to establish a miracle, unless the testimony be of such a kind, that its falsehood would be more miraculous, than the fact, which it endeavors to establish.

This does not, of course, mean that scientific research is a waste of time. Superstition and folk belief have an even worse track record than less-than-perfect science, and in the long run an understanding emerges from the rough-and-tumble of scientific disputation.

Suppose I get a positive result from a prostate-specific antigen test and want to estimate my posterior probability of having prostate cancer. For the prior, should I use the base rate for prostate cancer in the population? Among white Americans? Ashkenazi Jews? Ashkenazi Jews over sixty-five? Ashkenazi Jews over sixty-five who exercise and have no family history? These rates can be very different.