Of course , as with all second language (L2) data, these stages are not discrete or categorical and within each there is certainly individual variation. Nonetheless, it can generally be said that the rule of inversion is the major formal challenge for student and its mastery takes a while. The challenge is no doubt made more difficult by the fact that native speakers frequently do not invert questions in conversational English; hence, the input to which ESL/EFL learners are exposed is heterogeneous with regard to inversion. We return to this point later.