Navajo and Quechua, both languages with a highly complex morphology, provide intriguing insights into the acquisition of inflectional systems. The development of the verb in the two languages is especially interesting, since the morphology encodes diverse grammatical notions, with the complex verb often constituting the entire sentence. While the verb complex in Navajo is stem-final, with prefixes appended to the stem in a rigid sequence, Quechua verbs are assembled entirely through suffixation, with some variation in affix ordering.

We explore issues relevant to the acquisition of verb morphology by children learning Navajo and Quechua as their first language. Our study presents naturalistic speech samples produced by five Navajo children, aged 1;1 to 4;7, and by four Quechua-speaking children, aged 2;0 to 3;5. We centre our analysis on the role of phonological criteria in segmentation of verb stems and affixes, the production of amalgams, the problem of homophony, and the significance of distributional learning and semantic criteria in the development of the verb template. The phenomena observed in our data are discussed in light of several proposals, especially those of Peters, Pinker, Slobin, and Hyams.