Research demonstrates that object functions facilitate artifact categorization in infancy. To explicate the nature and magnitude of this effect, 16-month-olds participated in three studies. In Experiment 1, categorization was facilitated more by object functions than by distinctive motions, suggesting that the motion properties of function cannot fully explain its influence. In Experiment 2, infants failed to categorize when each category exemplar performed a different function, thus revealing the importance of shared functionality in facilitating categorization. In Experiment 3, infants were tested after each new exemplar was introduced. When object functions were provided during training, infants were more likely to appropriately extend the novel categories on the very first trial. This suggests that function reduces the need for exposure to multiple exemplars in forming categories. Together, these findings confirm the conceptual nature of the facilitative effect of function on early categorization. KeywordsCategorization; Function; Comparison; Causal relations; Infancy A wealth of evidence demonstrates that object function exerts a powerful organizing force on early categorization (Booth & Waxman, 2002;Greco, Hayne, & Rovee-Collier, 1990;Horst, Oakes, & Madole, 2005;Kemler Nelson, Frankenfield, Morris, & Blair, 2000;Nelson & Ware, 2002;Träuble & Pauen, 2007). Not only do object functions directly influence decisions that infants and toddlers make regarding category membership, they also facilitate the formation of new categories, exemplars of which can later be identified on the basis of less transient object properties (like shape or color). For example, Booth and Waxman (2002) demonstrated that 14-and 18-month-old infants extend novel artifact categories on the basis of perceptual similarity more readily when provided with information about object function than when exposed to other perceptual object properties alone.Infants in Booth and Waxman (2002) first observed an experimenter manipulate four examples of a novel artifact category. For some infants, the experimenter demonstrated how each object functioned on a uniquely designed apparatus while directing the infant to `look what I can do with this one.' For other infants, the experimenter simply picked up each object while directing the infant to `look at this one.' The experimenter then held up a contrast object drawn from a perceptually different category and highlighted that it did not © 2010 Elsevier Inc. All rights reserved Requests for reprints should be sent to Amy Booth, Roxelyn and Richard Pepper Department of Communication Sciences and Disorders, Northwestern University, Frances Searle Building, 2240 North Campus Drive, Evanston, IL, 60028. abooth@northwestern.edu.. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting...