It has been observed that when-questions are one of the last wh-questions produced by children learning English either as a first language (L1) or as a second language (L2). Explanations proposed for the late appearance of when-questions in L1 acquisition have been mostly based on cognitive factors. However, the cognition-based approach to when-questions faces problems in explaining L2 acquisition data, which show that L2 children who are cognitively more mature than L1 children follow the same developmental sequence. In this paper, I propose a possible explanation based on internal linguistic factors. According to Enç (1987), tense is a referential expression and temporal adverbials are antecedents of tense. I develop Enç's theory further and propose that in a when-question, tense is a bound variable, which is bound by the quantificational interrogative when. Thus, in order to produce when-questions, children must be at a stage where they understand bound variable readings. According to Roeper and de Villiers (1991), English-speaking children learn a bound variable reading approximately after 36 months, and the learning continues through the kindergarten years. The age at which a bound variable reading first appears corresponds to the point at which when-questions begin to occur. I propose that the complexity of the interaction between the quantificational when and tense, a bound variable, causes the delayed production of when-questions in developing grammars.
I IntroductionCross-linguistic studies on the acquisition of wh-questions have shown that both L1 and L2 learners produce wh-questions in the sequential order of where, what > how, who > why > when (this indicates that where and what are acquired before how and who, which is acquired before why, etc.) (