Most people never call an opponent vermin. The damage done in ordinary disagreement is usually smaller and more frequent: an eye roll, a sneer, a joke at someone's expense, a confident claim about what they "really" want. They also make it almost impossible for the person on the receiving end to hear anything else you say.

What marriages teach about arguments

Some of the best evidence on destructive disagreement comes from an unlikely place: the study of married couples. Starting in the 1970s, the psychologist John Gottman and his colleagues filmed couples discussing their conflicts and followed them for years. Gottman identified four patterns that he called the Four Horsemen: criticism, contempt, defensiveness and stonewalling. Criticism attacks a partner's character instead of a specific behavior. Defensiveness answers every complaint with a counterattack or an excuse. Stonewalling means shutting down and withdrawing from the conversation.

Of the four, Gottman found that contempt was the single best predictor of divorce. Contempt is not anger. Anger says "you did something wrong." Contempt says "you are beneath me," through mockery, sarcasm, name-calling or a curled lip. Contempt is corrosive because it denies the other person standing as an equal. Gottman also proposed antidotes. For stonewalling, his remedy was taking a break to calm down physically, since people who are flooded with stress cannot listen. For contempt, the remedy was building a habit of appreciation and respect. Political opponents are not spouses, but the same human reactions are at work.

Picking the weakest target

Most people know the straw man, a distorted and weaker version of an argument. Two subtler habits do the same work while seeming fair. The philosophers Robert Talisse and Scott Aikin described the weak man: attacking the weakest real argument someone on the other side has made, then acting as if the whole side had been refuted. Unlike a straw man, the weak argument really exists; somebody did say it. The trick is choosing it out of all the better arguments available.

A close cousin is nutpicking, a term coined by the blogger Kevin Drum in 2006: presenting the most extreme members of a group as typical of it. Social media makes nutpicking effortless, because among millions of people there is always someone saying something absurd, and outraged sharing guarantees that person a large audience. Combine nutpicking with the out-group homogeneity effect from Level 2 and an entire political camp can come to seem as foolish as its silliest member.

Love for us, hate from them

When people explain their own side's anger, they tend to see love: we fight because we care about our families, our country, our values. When they explain the other side's anger, they tend to see hate. In 2014 Adam Waytz, Liane Young and Jeremy Ginges documented this pattern among American Democrats and Republicans and among Israelis and Palestinians. They called it motive attribution asymmetry: the belief that one's own side acts from love while the other acts from hate. People who see their opponents as driven by hate find compromise pointless, since there is nothing to bargain with. Encouragingly, the researchers found that paying people for accurate answers reduced the asymmetry, which suggests that at least part of it is a lazy default rather than a deep belief.

Lincoln's drawer

One of the oldest tools for handling contempt is simple delay. After the Battle of Gettysburg in July 1863, Lincoln was furious that General George Meade had let the defeated Confederate army escape. He wrote Meade a blistering letter. Then he put it away. It was found among his papers after his death, marked "never sent, or signed." The practice of writing a "hot letter" and setting it aside unsent lets a person express contempt fully, to the page, without delivering it to a human being. In the age of instant replies, a draft folder can serve the same purpose as Lincoln's drawer.

None of this means feelings should be suppressed. Anger at real injustice is often appropriate and can drive change. The question is where the feeling is aimed: at an act, a policy or a system, which can be changed, or at a person's worth, which cannot be argued away.

Worked example: the family dinner

At a holiday dinner, Marcus mentions that he supports a new immigration restriction. His sister Lena laughs and says, "Of course you do. You've always been scared of anyone different." Marcus fires back that Lena's side "just hates this country." Their mother changes the subject and Marcus goes quiet for the rest of the meal.

Every horseman appeared in under a minute. Lena's laugh and her comment about fear were contempt and criticism of character. Marcus's reply was defensiveness, and also a clean case of motive attribution asymmetry: he assumed his sister's view came from hate rather than from her own kind of care. His silence afterward was stonewalling. A better version might begin with Lena asking what worries Marcus about the current system, and Marcus, if he still feels insulted, saying that he needs a few minutes before continuing. They might still disagree by dessert. But they would be arguing about immigration, not about whether the other is a decent person.