The 'root infinitive' phenomenon in child speech is known from major languages such as Dutch. In this case study, a child acquiring the Papuan language Nungon in a remote village setting in Papua New Guinea uses two different non-finite verb forms as predicates of main clauses ('root' contexts) between ages 2;3 and 3;3. The first root non-finite form is an apparent innovation of the child, unacceptable in adult-to-adult speech, which must be learned from a special auxiliary construction in child-directed speech. The second root non-finite form functions like attested adult main clause use of the same form. During the study period, the first root non-finite form increases sharply to function as a default verb form, then decreases to nil by 3;2. The second increases gradually to near-adult levels. Both forms are non-finite and have similar proportions in the input. Thus, factors other than finiteness and frequency must explain their distributions.
Keywords: Nungon; Papuan; acquisition; nominalizations; root infinitives; root nominal; verbs.