By Heart is a series in which authors share and discuss their all-time favorite passages in literature. See entries from Peter Stamm, Jonathan Franzen, Amy Tan, Khaled Hosseini, and more.

Harvard linguist and cognitive scientist Steven Pinker groups social reformers into two broad categories. The moralist condemns one behavior and promotes another; the scientist, on the other hand, tries to understand why human beings do the things they do, hoping self-knowledge will lead to positive change. In our conversation for this series, Pinker chose a favorite passage from Shakespeare’s Measure for Measure that illustrates both points of view—in its critique of human nature, Isabella’s speech swivels from detached observation to plaintive complaint. We discussed the limits of both science and moral judgments, and his belief that the analytic mindset is humanity’s best hope for a peaceful future.

Pinker’s most recent book, The Sense of Style: The Thinking Person’s Guide to Writing in the 21st Century, gives Strunk and White a much-needed OS update—while he acknowledges the merits of The Elements of Style, his book’s insightful introduction explains why a language can’t have one rulebook for two long. (Strunk and White suggested avoiding words like “geek” and “funky,” for instance, claiming they would fall quickly out of fashion.) The Sense of Style applies a linguist’s semantic chops to the questions of prose aesthetics, breathes fresh insight into grammar’s disputed territories, and takes stock of new developments in our ever-shifting American English.

In his previous book, The Better Angels of our Nature, Pinker argued that the years since World War II have been an era of unprecedented peace and stability. The author of many scholarly studies and popular books, including The Language Instinct, Pinker was named one of Time’s “100 Most Influential People in the World” in 2004. He spoke to me by phone.

Steven Pinker: In my book The Better Angels of Our Nature, I had two chapters on the psychology and neuroscience of violence. The first, “Inner Demons,” was on the systems in the human brain that cause people to engage in violence, namely revenge, dominance, sadism and exploitation. The other, “Better Angels,” was on the systems in the human brain that allow us to refrain from violence, namely compassion, self-control, reason, and moral norms.

This passage, taken from Shakespeare’s Measure for Measure, served as the epigraph to “Inner Demons”:

               But man, proud man,
Drest in a little brief authority,
Most ignorant of what he’s most assur'd;
His glassy essence, like an angry ape,
Plays such fantastic tricks before high heaven,
As make the angels weep.

Here, the character Isabella pleads for the life of her brother, Claudio, who has been condemned to be beheaded because he had impregnated his fiancée before they were married. Isabella appeals to the mercy and common sense of Angelo, a deputy who has  been temporarily put in charge of Venice.

The play reminds us of the ubiquity of puritanical legal codes and barbaric punishments through much of the history of civilization. It’s a reminder that the horrors of the Islamic State are nothing new: our own cultural tradition has had enough of it that it could serve as the backdrop for this famous play. Of course, by the time Measure for Measure was being performed—1604—theatergoers must have perceived decapitation for the offense of fornication as barbaric; that revulsion is the source of the play’s tension, as we sympathize with Isabella’s appeal to Angelo. In this way, the play is propelled by the kind of moral progress I write about. We witness the triumph of nonviolence over violence: Angelo does not, in fact, carry out the harsh sentence.

The passage itself is a mordant reflection on the flaws of the human moral sense. The subtitle of Harold Bloom’s Shakespeare: The Invention of the Human is a bit of an exaggeration, but it captures the fact that the bard was one of our first and greatest psychologists. Isabella compares the administration of an idealized divine justice with the all-too-fallible human justice. She reminds us that humans are capable of meting out patently cruel and pointless punishment judgments with complete confidence they are doing the right thing.

In the lines that precede the excerpt, we hear how Jove reserves the worst punishments for the hardest-hearted wrongdoers:

                Merciful Heaven,
Thou rather with thy sharp and sulphurous bolt
Split'st the unwedgeable and gnarled oak
Than the soft myrtle: but man, proud man…

Ideal punishments are proportional to the crime and the criminal. The gods would not use lightning to smite a “soft myrtle” but only the “gnarled oak,” the most obdurate kind of harmdoer. But “proud man” is more vengeful than Jupiter. I interpret the line “drest in a little brief authority” as referring not just to the fact that Angelo has only temporarily been put in charge by the absent Duke, but that all human claims to authority are, despite our pretensions to wise leadership, contingent and fleeting. The authority of rulers is insubstantial, our sense of justice fickle and haphazard.

Worse still, we humans are the last to notice our own limited nature. In seven words, Shakespeare sums up a good portion of the findings of modern psychology: “most ignorant of what he’s most assured.” A recurring discovery of social and cognitive psychology is that human beings are absurdly overconfident in their own knowledge, wisdom, and rectitude. Everyone thinks that he or she is in the right, and that the people they disagree with are stupid, stubborn, and ignorant. People reliably overestimate their own knowledge, and misjudge their own accuracy at making predictions. A common theme of both Shakespeare and modern social psychology is the human species’ overconfidence.

Remarkably, Shakespeare identifies this darker side with what we now know to be our evolutionary ancestry. With “like an angry ape,” he compares us to our primate cousins (an impressive 250 years before Darwin). What a striking simile for human impetuousness and foolishness! We tend to dignify displays of human emotion; presented with a burst of feeling, we seek its cause. But an angry ape we look on with amusement—the rage is infantile, comic, the result of ape’s own limited understanding. The detached amusement at the absurdity of human acts continues in the next line—“plays such fantastic tricks before high heaven.” “Playing a trick” refers to something lighthearted, trivial. Our feeble attempts at wisdom and justice, our petty exercise of power, appear ridiculous to wiser, celestial onlookers.

Then comes the shattering climax. With “as make the angels weep,” we experience an abrupt transition from the comic and absurd to the tragic and pathetic. It’s only at the very last word, “weep,” that the listener or reader is suddenly ripped into a different vantage point. From a detached perspective, the actions of humans laughable—we’re angry apes, we play tricks. But the human costs of human folly are no joke—they are tragic enough to make even the angels weep. What makes this passage so wrenching is that the shift from comic to tragic is concentrated in just two words: “angels weep.” Fittingly, they come at the end of the sentence. It’s a deep principle of style that the most information-rich or newsworthy part of a sentence should come at the end—and here, “weep” tonally trumps the comic antics that precede it. Yes, human beings are ridiculous, deluded, hilariously petty, comically misguided. But ultimately, these foibles have horrendous, lamentable consequences. Isabella’s reflection on the folly of human nature culminates in the tragic appreciation that absurd actions cause great suffering.

Indeed, this passage contrasts the two major perspectives that people adopt when it comes to other people’s behavior. There is the moralist’s perspective: behaviors that cause suffering are acts of pure evil, freely chosen. They are ultimately inexplicable and forever inexcusable. Then, there is the scientist’s perspective. The scientist seeks the cause of behavior. Scientists don’t judge, and they don’t weep; they ask why. Interestingly, the moralist’s perspective aligns with the perspective of the victim: this suffering is needless, inexplicable, avoidable, inexcusable. The scientist’s perspective, on the other hand, aligns with the perspective of the perpetrator: it seeks to rationalize and contextualize evil acts, the better to make sense of them. “I was just doing what anyone in that situation would do,” the perpetrator will often say—and the scientist, in subsuming the perpetrator’s act to some generalization about human behavior, seems to agree. Though the scientist has a different goal than the perpetrator—to understand, rather than to exculpate—their analytic stances overlap.

These two perspectives—that of the perpetrator or scientist, and that of the victim or moralist—color every analysis of human behavior. And here, we see Shakespeare suddenly flipping from one to the other for dramatic effect. It is the detached scientist’s perspective that likens humans to apes, that sees them as merely playing tricks. Suddenly we are yanked back to the perspective of the ultimate moralists: the angels.

Though the scientist’s viewpoint is often seen as cold, detached, amoral, I argue in the book that ultimately it can be more moral than the moralist’s. It is not enough to weep over tragedies, even when weeping is appropriate. We should also apply our analytic powers to explicate the motives that lead humans to do destructive things. And, paradoxically, it’s our moralistic impulses that often lead to the greatest destruction. That’s because, as Isabella observes, we are an ignorant and overconfident species. When we make moral judgments based on our parochial understanding of the world, we often do great harm.

Why is Angelo prepared to decapitate Claudio? It’s not for his own gain; he believes he’s implementing justice. He’s putting a law into practice and therefore acting as a moral agent; he firmly believes he’s doing the right thing. It’s his inability to see beyond the narrow framework of the conventions of his time and place, rather than any evil, self-serving motive, that in fact will lead him to commit an evil act.

History is replete with Angelos. If you were to add up the number of killings by people in pursuit of what they think are moral aims, whether it’s personal vengeance, implementing justice, or hastening a utopia or messianic age, the body count would surely be higher than the victims of amoral predation and exploitation.

That’s why pure moralism does more harm than good, and why a legitimate moral concern with human welfare must work together with a scientific drive to understand the causes of wrongdoing. If, as moralists, our responsibility is to reduce suffering and enhance flourishing, then the most powerful way to do that is through analytic engagement: moral philosophy, reasoned jurisprudence, legal scholarship, and the sciences of human nature. When we can say what makes us tick, we can rearrange our environments in ways that inhibit aggression and enhance empathy, compassion and reason.

To make the world a better place, we must be conscious of our cognitive and moral limitations. We must remain aware that we’re prone to imposing unreasonable judgments. When we mete out what we think is justice —“drest in a little brief authority”—we should be acutely aware of our fallibility in doing so. We are not angels, though we can imagine how we look to them.