Book SummaryRationality, by Steven Pinker

1-Page Summary1-Page Book Summary of Rationality

What does it mean to be rational? Why is being rational important? How can you be a more rational person? In Rationality, Steven Pinker argues that rationality and reason are essential for improving our world and society, but that people often misunderstand them, acting irrationally even when they think they’re not. He examines how you can be more rational and make better decisions by improving your critical thinking skills and by understanding—and thus avoiding—the logical fallacies and cognitive blunders that people often fall victim to.

Steven Pinker is a cognitive psychologist whose best-selling works include _[The Stuff of...

Rationality Summary What Is Rationality?

Pinker defines rationality as the use of knowledge to attain goals. Within this definition, knowledge is a belief that can be proven true. Both of these aspects—goals and true, provable knowledge—are critical aspects of rationality. You’re not acting rationally if you act on false beliefs, nor are you acting rationally if you don’t apply your beliefs to a goal—a rational person must have a purpose for their thinking, whether that be to get around a physical object or to determine the truth of an idea.

**The Cognitive Versus Emotional...

Rationality Summary Why Rationality Matters

Pinker contends we as humans have a moral obligation to think rationally, for two reasons.

First, rationality is moral because it’s through rationality that we build a better society. Reason has enabled us to make valuable discoveries, inventions, and social progress that have allowed humans to live better lives. Because we have a moral imperative to improve the world and the lives of others, and since rationality is a key aspect of our ability to do so, we have a moral obligation to think rationally.

Second, morality hinges on agreement on right and wrong. Reason allows us to think impartially, consider conflicting interests, and determine what contributes to the common good. Because rationality is the only thing that allows us to come to a collective consensus on anything, it’s the only way to prevent one group...

Rationality Summary Rational Choice Theory

Pinker explains that economists, philosophers, and others have defined rationality using the rational choice theory, which states that people will choose between options with the aim of maximizing the rewards of their decision.

More specifically, when making a rational decision, a person considers the possible outcomes of each option, judges how much they want (or don’t want) each outcome, and considers how likely each outcome is to happen. This analysis yields an option’s “expected utility”: its potential rewards weighted by both desirability and probability. A rational person then chooses the option with the highest expected utility.

For example, if someone is deciding if they should pack a warm coat for a trip, they’ll first weigh the possible outcomes of each option by desirability. If the weather gets cold, they’ll be happy they packed the coat. But if the weather ends up being warm, they’ll be annoyed that they wasted space in their suitcase on such a bulky and heavy item. They’ll then weigh the likelihood of each option: Is it more likely the weather will be cold or warm? And from there, they’ll decide which option has the highest expected utility, and they’ll...

Rationality Summary Logic and Critical Thinking

Pinker writes that one of the main reasons people think irrationally is that they use logic and critical thinking incorrectly. Critical thinking (also known as deductive reasoning) is the ability to accurately assess logic—to judge whether a conclusion is true based on its premises.

(Shortform note: In Blink, Malcolm Gladwell differentiates between two systems of thought that we use to arrive at decisions: conscious and unconscious. Our conscious minds think critically and weigh logical arguments, and our unconscious minds produce snap judgments that we sometimes can’t fully explain. While Pinker argues that deductive reasoning, which comes from our conscious mind, is the superior method of decision-making, Gladwell contends that our snap judgments can often produce better decisions because our subconscious brains are remarkably effective at sorting through and ignoring irrelevant information—details that can trip us up when we try to consider all possible premises logically when arriving at a conclusion.)

People often misinterpret logic and...

Rationality Summary Probability

Pinker writes that an important aspect of rationality is understanding how probability works and using it to make better decisions.

Probability can be best understood as the chance that an event will happen given the opportunity. When someone says there is a 50% chance of an event occurring, this means it will happen 50 out of 100 times, on average. If you flip a coin 100 times, the head-to-tail ratio may not be exactly 50-50, but there’s still a 50% chance of either heads or tails with every flip.

(Shortform note: The authors of Superforecasting note that probabilities are only estimates, and predicting the occurrence of a real-world event is nearly impossible since it would require rewinding history and replaying the event multiple times to see all the different possible outcomes. Thus it’s important to keep in mind that the probabilities that most forecasters are concerned with—for example, election outcomes—are essentially their best guesses, not objective facts.)

People often miscalculate the probability of an...

Rationality Summary Correlation Versus Causation

Pinker next turns his attention to problems that people run into when considering causation and correlation, which drive them to make irrational decisions.

A common mistake people make is thinking that events that are correlated (they often happen at the same time) are causing each other, when in fact they might be linked simply by coincidence or by a third factor. This can lead people to make poor decisions—when they think the wrong event causes another, they incorrectly predict the future.

For example, if the stock price of a company always rises in November, a person might think the arrival of November causes the price to rise, and they might then buy stock in October in anticipation of that rise. However, if the true reason behind the price increase is that the stock rises when the company offers a huge sale on their goods, which they happen to always offer in November, then the person buying stock in October might lose money if the company decides not to offer that sale this particular November. If the person had correctly identified the causal link (between the sale and the price rise, instead of between the month and the price rise), they might have...

Rationality Summary Rationality and Game Theory

Thus far, we’ve examined how people make rational decisions at an individual level. We’ll now look at how people make decisions as part of a group. This brings us to game theory, which examines how rationality is affected when the needs of an individual are pitted against the needs of others.

We’ll first look at how game theory shows that sometimes, acting irrationally can be the most rational choice, and we’ll then examine how people can be convinced to make rational choices when they’ll only see benefits from those choices if everyone else chooses rationally as well.

(Shortform note: In The Undercover Economist, Tim Harford defines a game as an activity in which predicting another’s actions affects your decisions. With this definition, many situations in our lives can be considered games, like driving, where how you drive depends on how others are driving.)

The Zero-Sum Game

Pinker first examines how game theory shows that sometimes, a rational person must make choices that are, on their face, irrational, such as when opposing...

Rationality Summary Why Humans Are Irrational

So, Pinker asks, given that most people agree on the importance of rationality and its basic characteristics, why do people often act irrationally? Why do people hold irrational beliefs—-such as paranormal phenomena or conspiracy theories?

Pinker notes that social media has allowed people to express their irrational beliefs loudly, which makes it seem that irrational thought is a growing and recent phenomenon, but, he argues that people have believed these types of ideas for millennia. Aside from all the fallacies and biases that we just covered, Pinker discusses two additional causes of such human irrationality in the modern world: motivated reasoning and myside thinking.

(Shortform note: The examples of irrational beliefs that Pinker mentions are, indeed, only recent examples of a phenomenon dating back to ancient times. For thousands of years, for example, people have believed in shadowy groups controlling the world, right back to the ancient Egyptians complaining of Grecian priests who held secret knowledge and the 18th-century belief in the [Order of the...

Shortform Exercise: Examine Your Myside Thinking

Consider how myside thinking might be affecting your beliefs or your interactions with others.

How closely do you consider your political beliefs to align with the people closest to you? Do you associate with people at work or in your personal life who hold significantly different views than you?