Name: Rationality
Rating: 4.2 (393 reviews)
Author: Steven Pinker

What’s in it for me? Learn how reason really works.

It’s safe to assume that no human has ever been perfectly rational, but the conviction that objective truth exists has allowed us to create rules that help us approach it.

When you follow those rules, the author argues, you can change the world.

It’s rationality, for example, that helped us reach the moon, eradicate diseases like smallpox, invent computers, and, more recently, develop a vaccine against a deadly global pandemic in just one year.

So what are those rules – how does rationality work and how can you cultivate it? That’s exactly what we’ll be exploring in these blinks!

Along the way, you’ll learn

why ignorance can be a rational choice;
what counting horse teeth can teach us about science; and
why our fear of being suckers erodes public services.

Rationality is a means to an end.

Let’s start at the beginning: what is rationality? Dictionaries tell us that rational means “having reason.” And reason comes from the Latin word ratio, which means – you guessed it – “reason.”

So, if etymology leads us in circles, could philosophy help? Philosophers state that rationality is the ability to use knowledge to attain goals. Better?

Let’s break that down. The term knowledge refers to justified true beliefs. We wouldn’t credit someone with being rational if they knowingly acted on false beliefs – like looking for a misplaced wallet someplace they knew it couldn’t be. But there’s more to rationality than simply thinking true thoughts like “1 + 1 = 2.” It also helps us do things.

The key message here is: Rationality is a means to an end.

In 1890, the American philosopher William James wrote an essay on the difference between rational beings and nonrational entities.

James observed that if you scatter iron filings on a table and place a magnet near them, they fly toward the magnet and stick to its surface. But cover the magnet with a card and they press against its surface – it never occurs to them to bypass the card and come into direct contact with the object that attracts them. Now consider Shakespeare’s Romeo and Juliet.

Juliet is Romeo’s “magnet.” When there’s no obstacle in his path, he moves toward her in a straight line just as the filings moved toward the real magnet. But here’s the difference. When Romeo finds his path blocked, he alters course. Romeo and Juliet don’t remain on either side of this obstacle, “idiotically pressing their faces against its opposite sides like the magnet and the filings with the card.”

In the play, Romeo and Juliet use their knowledge of the world to overcome hurdles. Romeo scales walls to touch Juliet’s lips, and the couple scheme to deceive their hostile families.

For James, this is what sets nonrational entities and rational beings apart. Iron filings move in a straight line toward their goal. But their path to that goal is fixed – that’s why the card impedes them so easily. It’s the other way round for rational beings. Romeo and Juliet’s desired end – being together – is fixed, but they’re highly flexible about how they achieve that goal.

This is human rationality in action: when one path is blocked, we can always try another.

Rationality helps you decide between passions.

We’ve just argued that reason is a means to an end. But where do the goals which it helps us pursue come from? One answer comes from the eighteenth-century Scottish philosopher David Hume.

Goals, Hume claimed, come from the passions. That is, from desires, drives, and emotions like love, anger, pride, envy, and fear. Reason, meanwhile, is the “slave of the passions.”

Punishing people for their own good creates a more rational commons.

If you want a better view of the stage at a concert, it makes sense to stand up. But that obscures the view of others, so they also get up. Soon, everyone is on their feet and no one has a better view.

Arms races follow the same logic. If one country spends lots of money developing long-range missiles, it becomes rational for its hostile neighbor to do the same thing, leaving both countries poorer.

Our most important moral idea is compelling because it’s rational.

As we’ve seen, secular laws can force us to take care of the public good. Many believe religious laws do something even more important: they force us to be moral.

That argument has been around for a long time – so long, in fact, that it was familiar to Plato 2,400 years ago. But does it hold up? The Greek philosopher didn’t think so.

Key ideas in Rationality

What is Rationality about?

Rationality (2021) explores the faculty that sets us apart from other species: reason. The ability to think rationally drives individual and social progress. It allows us to attain our goals and create a fairer world. But rationality isn’t just something we do as individuals – it also sustains our best institutions.

About the Author

Steven Pinker is the Johnstone Professor of Psychology at Harvard University and an award-winning author. A member of the National Academy of Sciences, he’s been named one of Time’s 100 Most Influential People and one of Foreign Policy’s 100 Leading Global Thinkers. His previous books include Enlightenment Now and The Better Angels of Our Nature.