Most modern humans live in large-scale societies filled with strangers. How can we navigate these societies without social life descending into conflict and chaos? Since Plato, social theorists have primarily pointed to institutions like legal codes and moralizing religions for enforcing and coordinating large-scale cooperation. Here, I will outline the role of social psychological heuristics that help people infer their partners’ cooperative intent, priorities, and abilities. I suggest that these heuristics are more widespread than previously acknowledged. Concepts like “morality,” traits like “agreeableness,” and social identities like “Christian” are all socially constructed heuristics that help us use known information to infer the contents of unknown minds. I will present a stream of research combining field research in small-scale societies, laboratory experiments, cross-cultural surveys, and natural language processing analyses to show how various social heuristics evolve in large-scale societies.