The purpose of this research is to examine an analysis of research studies into the issue of how children acquire the competence to invert subject and auxiliary-verb placement (subject auxiliary inversion or SAI) in sentences. The plan of the research will be to set forth the pattern of ideas in the analysis and then to discuss the apparent relevance and importance of the ideas to the study of language acquisition.
Once children have lexically acquired auxiliary verbs, they quickly begin to acquire what are referred to as SAI triggers, thence beginning to form interrogative statements, or WH-phrases (599). Errors made in the early-stage use of WH-phrases indicate "that the function of the auxiliary has not been grasped" (600) at the level of syntax. Acquisition of adult-like WH-movement is distinguished from "formulaic WH expressions" (603) and involves evidence of the ability to select an appropriate semantic complement that is not tied to the formula or an auxiliary verb with a verb that is already used without WH-words. Both WH-movement and acquisition of the auxiliary system appear to be grasped at approximately the same time in language development.
Order of acquisition or developmental sequence of WH-words in children's language acquisition has been identified as follows: (a) what/where; (b) why/how; (c) who; (d) which X/how X. The developmental sequence has been attributed to such variables as "frequency of input" (607). In this view, what and where are associated with here-and-now identification of things, while why and how entail reasoning, a much less likely foundation for (parental, e.g.) inputs to the child. Another relevant variable is "cognitive difficulty" (608) or the child's ability to grasp meanings associated with the child may have lexically acquired. A third variable is described as the properties of the learning mechanism, which refers to the child's sensitivity to distinctions between differences of kind an...