The Inclusion of Disjunction in Child Grammar: Evidence from Modal Verbs

This study is concerned with the acquisition of the disjunction operator, or, in English. Two mutually inconsistent claims have been made about the acquisition of disjunction. One claim is that the acquisition of the adult truth conditions for logical connectives, including disjunction, is a late and not fully universal, achievement. With particular reference to disjunction, the findings from several studies are interpreted as showing that only the truth conditions associated with exclusive-or are available to young children (e.g., Beilin and Lust 1975; Braine and Rumain 1981, 1983; Paris 1973). There is a related claim, that even when children respond as if they have access to a broader range of truth conditions, namely those associated with inclusive-or, children's adult-like responses are the result of a failure to distinguish or from and (Paris 1973). A different conclusion was reached in a recent study by Chierchia, Crain, Guasti and Thornton (1998), who conducted a series of experiments which revealed children's adult-like knowledge of logical connectives, including disjunction. To reconcile the findings from the Chierchia et al. study and those of previous research, Chierchia et al. (1998) draw upon a distinction between semantic and pragmatic knowledge. They argue that the acquisition of logical connectives is simply a process of mapping the appropriate truth conditions (associated with logical connectives in classical logic) onto the particular words of the language to which the child is exposed. In understanding sentences, however, children are also influenced by the pragmatic norms they follow. In many..