The world is complicated, and our minds have limited capacity, so we create categories to help us make sense of things. We divide, say, the social world into types — hipster, evangelical, nerd, white or Black — and associate traits or characteristics with each.

These judgments involve simplifications and generalizations. But we couldn’t make sense of the blizzard of sensory data each day if we couldn’t put things, situations and people into some form of conceptual boxes. As Immanuel Kant argued, perceptions without conceptions are blind.

It becomes a serious problem when people begin to believe that these mental constructs reflect underlying realities. This is called essentialism. It is the belief that each of the groups we identify with our labels actually has an “essential” and immutable nature, rooted in biology or in the nature of reality. In the worst kind of case, it’s the belief that Hutus are essentially different from Tutsis, that Christian Germans are innately superior to Jews.

Essentialism can produce certain common habits of mind. Essentialists may imagine that people in one group are more alike than they really are and are more different from people in other groups than they really are. Essentialists may believe that the boundaries between groups are clear and hard and anybody adopting the culture of another group is guilty of appropriation. Essentialists may see the world divided into Manichaean dichotomies, and history as a clash of group-versus-group power struggles — clashes that demand utter group solidarity and give life meaning.

America is awash in essentialism. As the New York University philosophy professor Kwame Anthony Appiah, who writes the Ethicist column for The Times Magazine, has noted, before World War II few thought about identities the way we do today. But now it feels that contemporary politics is almost all about identity — about which type of person is going to dominate.

At some level this is necessary. The great project of the past 70 years or so has been to right the injustices that historical essentialists imposed on groups they labeled and oppressed.

The problem comes when people replicate the mindset they are fighting against. The Johns Hopkins political scientist Yascha Mounk observed that there are at least two large social movements in American life on different spots on the essentialist spectrum. On the right, there is “the ethnonationalist, white nationalist position that race is real and it will always be there, and societies will thrive insofar as the supposedly superior group manages to stay in charge.” On the left there is the tendency that holds “that race is so essential and so deeply baked in that it will always define communities and societies, and rather than having a liberal democracy in which we primarily are seen as individual citizens with the same rights and duties, we should primarily be seen as members of our racial or perhaps religious communities.”

When essentialist groups go at each other, sweeping generalizations have a tendency to fill the air. You run across workshops on topics like “What’s Up With White Women?” as if all the white women in the world were somehow one category. You get a Trump-endorsed gubernatorial candidate in Arizona pledging to take a sledgehammer to a category of people called the “corrupt media” and charging the “corporate media establishment” with employing methods “right out of a communist playbook.” Politics is no longer about argument; it’s just jamming together a bunch of scary categories about people who are allegedly rotten to the core.

Some people say the thing to do is to drop the group mentality entirely. Judge people as individuals only. That seems unrealistic to me, and even undesirable as an aspirational ideal. I wouldn’t want to live in a world that didn’t have group consciousness, a world without Irish people singing about Irish history, without Black writers exploring different versions of the Black experience.

But we can have groups without essentialism, we can become more intolerant of the essentialist cast of mind. That begins by acknowledging, as Appiah has observed, that all our stereotypes are wrong to some degree. I would add, they are always hurtful to some degree. We should be much more suspicious of our categories, much quicker to acknowledge that they are sometimes helpful but always simplistic fabrications.

It requires social courage, crossing group lines to have conversations. When we have conversations with people in other groups, we take the static world of essentialism and turn it into flux. In conversation people are not objects, but ongoing narrators of their own lives, navigating between their multiple identities, steering through certainties and doubts, and refining their categories through contact with others.

We’re a big diverse country; whether we see that diversity through a fixed mindset or a growth mindset makes all the difference.

Brooks is a columnist for The New York Times.