Maturation and the Acquisition of the Sesotho Passive

Borer & Wexler 1987 explain the apparent late acquisition of verbal passive in English and Hebrew by hypothesizing that the principle governing A-chain formation matures relatively late in language development. However, in Sesotho, a Bantu language, verbal passives are acquired early, by at least 2;8 years. This suggests either that English- and Hebrew-speaking children actually acquire the ability to form verbal passives early in language development, and that other nonmaturational factors influence its late appearance, or that the acquisition of the verbal passive is not determined by maturation, contrary to the claims of Borer & Wexler.