THE POWER OF US explores the dynamics of shared, social identities. What causes people to develop social identities? What happens to people when they define themselves in terms of group memberships? Under what conditions does the human proclivity to divide the world into “us” and “them” produce toxic conflict, paralyzing polarization, and devastating discrimination? And how can shared identities instead be harnessed to improve performance, increase cooperation, and promote social harmony?

Aristotle famously said that “knowing yourself is the beginning of all wisdom.” But we argue that truly knowing yourself is not about trying to pin down an essence, a stable and immutable command of who you are. Instead, knowing yourself is about understanding how your identity is shaped and reshaped by the social world that you are inextricably embedded in—as well as how you shape the identities of people around you.

Drawing upon research in social psychology and cognitive neuroscience, as well as the social sciences more generally, we advance a set of identity principles. Groups are central to how people define themselves. The most important groups in people’s lives and thus their most central social identities are often quite stable. And yet we also have a readiness for solidarity with strangers, which allows us to find common cause around emergent identities. Different identities become salient at different times—and when a particular social identity is active, it can have profound effects on our thoughts, feelings, and behaviors. 

Shared identities provide the foundation for a great deal of human coordination, collaboration, and prosociality. But there is a flipside to this: cooperation and generosity are often bounded. Social identities can make people want to help members of their own groups, but it can also make them want to harm—or at least avoid helping—people who belong to other groups. 

When an identity is active, people experience the world through the lens it provides, embrace a shared reality with fellow group members, and find joy in group symbols and traditions. People will sacrifice, even fight, to protect the interests of the group. These shifts in perceptions, beliefs, feelings, and actions often align people with the norms of the group. And when leaders lead and others follow, it is often by inspiring a shared sense of “who we are.”

Despite their power to shape our thoughts and behaviors, human identities are also the site of our agency. Whether by rejecting or embracing a particular conception of ourselves, by challenging our groups to be better or by organizing in solidarity to change the world, we take control of who we want to be.