Despite modernity’s love affair with rationality and the precision that supports it, ambiguity persists not only in humor and politics but in all areas of contemporary life including scholarship and science. Here the authors explore how knowledge cultures differ in their precision of expression and the consequences of ambiguity for those cultures. They develop, estimate, and validate a model of ambiguous expression from large-scale publication data and then show that ambiguous scholarly language acts like a boundary object between researchers and their communities, drawing competing interpretations into conversation with one another as they build on it. Ambiguity, and the uncertainty that follows, stimulate social learning and so ironically play a crucial role in focusing modern knowledge and creating zones of social and intellectual engagement.