An experimental-clinical analysis of grammatical and behavioral distinctions between verbal auxiliary and copula

The study was designed to investigate whether auxiliary is and copular is belong to a single response class. Two children acted as subjects. The auxiliary verb was trained, then reversed, and later reinstated in one of the subjects, while the copula was similarly trained, reversed, and reinstated in the other child. Both the auxiliary and the copular sentences were tested on probes. The first subject, who was trained only on the auxiliary, was able to produce the untrained copula. When the auxiliary production was reversed, the copular production also was reversed. Finally, when the auxiliary production was reinstated, the copular production also was reinstated. For the second subject, the auxiliary production was generated, reversed, and reinstated by training, reversing, and reinstating only the copula. These results suggest that the copular and auxiliary is belong to a single response class and training either of them is sufficient to generate the production of both.