Recent research documents that for infants just beginning to produce words on their own, novel words highlight commonalities among named objects and, in this way, serve as invitations to form categories. The current experiment identifies more precisely the source of this invitation. We asked whether applying a consistent name to a set of distinct objects is crucial to categorization, or whether variable names might serve the same conceptual function. The evidence suggests that for 12-month-old infants, consistency in naming is critical. Infants hearing a single consistent novel noun for a set of distinct objects successfully formed object categories. Infants hearing different novel nouns for the same set of objects did not. These results lend strength and greater precision to the argument that naming has powerful and rather nuanced conceptual consequences for infants as well as for mature speakers.