A study was conducted to test the hypothesis that metaphorical thought develops according to the principles governing other categorizing processes. Of particular interest were the questions of whether preschool children possess the categorical flexibility to comprehend metaphorical statements and, if they do, whether this flexibility manifests itself across the perceptual, functional, and affective domains simultaneously or at different stages in development. In total, 150 predominantly middle- to upper-middle-class subjects (15 males and 15 females from each of several grade levels) participated in the study. Subjects were enrolled either in kindergarten; in third, sixth, or ninth grades; or in college. Eight sets of metaphors were used in the study, with each set containing eight metaphors beginning with the same "topic" (X) term within the statement "X is (a) Y.""Vehicle" (Y) terms were varied to convey perceptual, functional, or affective similarities between topic and vehicle. (For example, the items "eyes are marbles,""eyes are cameras,""and "eyes are shy children" illustrate, respectively, a perceptual, functional, and affective metaphor.) Matching foils were created for each genuine metaphor by leaving topics intact and substituting words of similar vocabulary to create nonsensical expressions. Subjects were asked to listen to each of 48 items, say "yes" if the item made sense to their imagination or if it could go in a story or poem, and say "no" otherwise. Results were found to challenge prevailing opinions concerning the development of metaphor comprehension. (RH)