Abstract Recent research has documented that for infants as young as 12–13 months of age, novel words (both count nouns and adjectives) highlight commonalities among objects and, in this way, foster the formation of object categories. The current experiment was designed to capture more precisely the scope of this phenomenon. We asked whether novel words (count nouns; adjectives) are linked specifically to category-based commonalities from the start, or whether they also direct infants' attention to a wider range of commonalities, including property-based commonalities among objects (e.g. color, texture). The results indicate that by 12–13 months, (1) infants have begun to distinguish between novel words presented as count nouns versus. adjectives in fluent, infant-directed speech, and (2) infants expectations for novel words accord with this emerging sensitivity.