Few constructions in child's production can be considered originals and not mere copies (partial or complete) of adult input. These rare constructions are precious to child language studies because they may reveal a developmental process at work. One of them is children's left-dislocated subjects. In French, when there is no lexical subject, the use of a subject pronoun is mandatory. When there is a lexical subject, two constructions are possible: one with the use of a personal pronoun and one without. Children tend to produce a lot of pronouns in the context of lexical subjects, which makes it a good candidate for being a specific feature of child language.
This study used two corpora of spontaneous language production, one with children aged three to four and one with children aged two to four. The data were analyzed using Tomasello's framework (usage-based theory of language acquisition). In this theory, children's language competence differs from the adults' and develops with age. The first issue was to demonstrate the existence of this specific feature. Indeed, it appeared that children produced more left-dislocated subjects than adults and did not simply reproduce a feature of adults' oral language. The presence of a developmental effect in the children's production was also strongly suggested by the results.
The second issue was to try to better understand what could be the reason for the difference in production of left-dislocated subjects between children and adults. Several explanations of the children's results were put forward, in keeping with the predictions of the usage-based theory. Lexical and usage-based explanations of children's behaviour were shown to be unlikely. More plausible explanations were performance limitation or a consequence of the development of the use of personal pronouns, even when they are not obligatory.
It is proposed that children's left-dislocated subjects should not be considered as a copy of adults', but as a specific construction pattern that appears during the course of language development. This pattern could provide a path towards the development of more general linguistic abstractions, as proposed in the usage-based theory.