When Zohran Mamdani took office as the mayor of New York City on 1 January, he promised to usher in a transition from “the frigidity of rugged individualism to the warmth of collectivism.” It was a bizarre and stilted choice of words. “We will govern expansively and audaciously,” he told the people. The message was clear: New York’s political culture was about to change. Mamdani would institute free buses, a rent freeze, universal childcare, and higher taxes on wealth.

The people around Mamdani have been unusually candid about what the new mayor meant by “collectivism.” The Director of the Mayor’s Office to Protect Tenants, Cea Weaver said, “the reality is that for centuries, we have really treated property as an individualised good and not a collective good. And we are going to transition into treating it as a collective good and toward a model of shared equity.” Weaver was clear that this won’t be costless. “It will mean that families, especially white families but some POC families who are homeowners as well, are going to have a different relationship to property than the one that we currently have.”

But once you get into the mechanics of this, you quickly run into problems. New York contains eight million people, making millions of daily decisions: where to live, what rent to charge, which job to take, how to run a small business. Each decision rests on local knowledge—information that exists in fragments, held by individuals who understand their own circumstances and priorities in intimate detail.