Acquisition of Default Inflectional Suffixes: Japanese Adjectives Miho Fujiwara This study examines the acquisition of two adjectival inflectional classes in Japanese. Ten children (ages 4 and 5) and 24 adults were asked to provide the past-tense form of existing and novel adjectives, which they heard in their nonpast form. The results show that the past-tense form for one inflectional class is acquired earlier than the other and overgeneralized for both existing and novel adjectives. Interestingly, this is not the default form adults extend productively to novel adjectives. However, once the other inflectional class is acquired, children, like adults, use this form as the default. The results also show that children do not use the morphological information (i.e., suffix) in the stimuli as effectively as adults in determining class membership of novel adjectives. These results raise interesting learnability questions regarding why one form is learned earlier than another, what the mechanism is for identifying inflection-class membership, and how children (re-)learn the correct default class for adjectives.