How do infants learn that a bottle is different from a glass, and what is the role of language in this learning process? In a series of experiments, Xu takes one step towards answering these questions by investigating whether babies use words to individuate objects [ 1. Xu F. The role of language in acquiring object kind concepts in infancy. Cognition. 2002; 85: 223-250 Crossref PubMed Scopus (223) Google Scholar ]. Nine-month old babies saw two objects being brought out from behind a screen and replaced, one at a time. In one condition, the objects were labeled with two different nouns (‘Look, Maggie, a ball … Look, Maggie, a duck’). In another condition, only one word was used for both objects (‘Look, Maggie, a toy’). This procedure was repeated several times. Next, the screen dropped revealing either both, or one of the objects. Babies looked longer at the one-object than the two-object display, but only in the two-word condition. This suggests that the babies used the different words to individuate the two objects, and were therefore more surprised when one rather than two objects remained. Similar results were obtained when nonsense words and nonsense objects were used, showing that previous exposure to the words and objects was not essential. By contrast, babies did not show more surprise at the one- compared with two-object outcome when the objects were labeled with two tones, two non-linguistic sounds or two emotional expressions (positive-sounding ‘ah’, negative-sounding ‘ewy’).