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

by Steven Pinker

Foremost among informal fallacies is the straw man, the effigy of an opponent that is easier to knock over than the real thing. “Noam Chomsky claims that children are born talking.” “Kahneman and Tversky say that humans are imbeciles.” It has a real-time variant practiced by aggressive interviewers, the so-what-you’re-saying-is tactic.

They can move the goalposts, demanding that we “defund the police” but then explaining that they only mean reallocating part of its budget to emergency responders. (Rationality cognoscenti call it the motte-and-bailey fallacy, after the medieval castle with a cramped but impregnable tower into which one can retreat when invaders attack the more desirable but less defensible courtyard.)

These tactics shade into begging the question, a phrase that philosophers beg people not to use as a malaprop for “raising the question” but

Another diversionary tactic is called tu quoque, Latin for “you too,” also known as what-aboutery. It was a favorite of the apologists for the Soviet Union in the twentieth century, who presented the following defense of its totalitarian repression: “What about the way the United States treats its Negroes?” In another joke, a woman comes home from work early to find her husband in bed with her best friend. The startled man says, “What are you doing home so early?” She replies, “What are you doing in bed with my best friend!?” He snaps, “Don’t change the subject!”

A related tactic is the genetic fallacy, which has nothing to do with DNA but is related to the words “genesis” and “generate.” It refers to evaluating an idea not by its truth but by its origins.

Sometimes the ad hominem and genetic fallacies are combined to forge chains of guilt by association:

Then there are arguments directly aimed at the limbic system rather than the cerebral cortex. These include the appeal to emotion: “How can anyone look at this photo of the grieving parents of a dead child and say that war deaths have declined?”

The ad hominem, genetic, and affective fallacies used to be treated as forehead-slapping blunders or dirty rotten tricks. Critical-thinking teachers and high school debate coaches would teach their students how to spot and refute them. Yet in one of the ironies of modern intellectual life, they are becoming the coin of the realm. In large swaths of academia and journalism the fallacies are applied with gusto,

Logical reasoning in the strict sense means forgetting everything you know. A student taking a test in Euclidean geometry gets no credit for pulling out a ruler and measuring the two sides of the triangle with equal angles, sensible as that might be in everyday life, but rather is required to prove it.

As the economist Max Roser points out, news sites could have run the headline 137,000 People Escaped Extreme Poverty Yesterday every day for the past twenty-five years.33 But they never ran the headline, because there was never a Thursday in October in which it suddenly happened.

In their “Ignorance Project,” Hans and Ola Rosling and Anna Rosling-Rönnlund have shown that the understanding of global trends in most educated people is exactly backwards: they think that longevity, literacy, and extreme poverty are worsening, whereas all have dramatically improved.

Consumers of news should be aware of its built-in bias and adjust their information diet to include sources that present the bigger statistical picture: less Facebook News Feed, more Our World in Data.

Journalists should put lurid events in context. A killing or plane crash or shark attack should be accompanied by the annual rate, which takes into account the denominator of the probability, not just the numerator. A setback or spate of misfortunes should be put into the context of the longer-term trend.

the state of the art in scientific methodology is to “preregister” the details of a study in a public registry that reviewers and editors can check for post hoc hanky-panky.

The cluster illusion makes us think that random processes are nonrandom and vice versa.

Bayes’ rule or Bayes’ theorem is the law of probability governing the strength of evidence—the rule saying how much to revise our probabilities (change our minds) when we learn a new fact or observe new evidence.

You may want to learn about Bayes’ rule if you are: A professional who uses statistics, such as a scientist or doctor; A computer programmer working in machine learning; A human being.

translated into common sense, it works like this. Now that you’ve seen the evidence, how much should you believe the idea? First, believe it more if the idea was well supported, credible, or plausible to start with—if it has a high prior, the first term in the numerator. As they say to medical students, if you hear hoofbeats outside the window, it’s probably a horse, not a zebra.