Published online by Cambridge University Press: 19 February 2026
The hypothesis that children's errors in interpreting adjunct PRO clauses are due to their use of a nominal structure was tested in two act-out experiments. Four- to six-year-old English-speaking children permitted a by phrase inside an adjunct clause containing an intransitive verb to be interpreted as agentive, and they gave such an interpretation for a construction for which a nominal analysis is not permitted in the adult grammar (when PRO clauses). This behavior can be accounted for if children have knowledge of general principles governing the interpretation of nominal and PRO constructions, and use a nominal analysis in interpreting adjunct clauses. In the second experiment, children distinguish between constructions that are unambiguously nominal and those that are ambiguous between a nominal and PRO structure, permitting agentive readings of by more frequently in the former case. This argues that adjunct PRO may be acquired by some children at a point during the preschool years. Overall the results fit a view of acquisition in which the language learner actively analyzes the input data, using knowledge of general grammatical principles, and is not narrowly bound by his or her current knowledge of the lexicon of the language.