Comparison mechanisms have been implicated in the development of abstract, relational thought, including object categorization. D. Gentner and L. L. Namy (1999) found that comparing 2 perceptually similar category members yielded taxonomic categorization, whereas viewing a single member of the target category elicited shallower perceptual responding. The present experiments tested 2 predictions that follow from Gentner and Namy's (1999) model: (a) Comparison facilitates categorization only when the targets to be compared share relational commonalities, and (b) providing common labels for targets invites comparison, whereas providing conflicting labels deters it. Four-year-olds participated in a forced-choice task. They viewed 2 perceptually similar target objects and were asked to "find another one." Results suggest an important role for comparison in lexical and conceptual development.