This paper deals with deep and surface structure differences and their implication for language teachers. Examples of similar surface structures and dissimilar underlying structures often presented to students of English for pattern drill are pointed out (e.g., the "it" in "It's easy to speak English,""It's difficult for us," and "It's hot outside," reflects respectively, extraposition, pronominalization, and association with the weather). English as a second language materials are oriented almost invariably toward imparting as a final goal the ability of the student to give phonological shape to surface structures. The author considers mastery of deep structure principles as important, if not more so, since it is these which govern semantic interpretation. Because control by the student over deep structure differences will not take place unless he is aware of them, one of the aims of language pedagogy must be to bring about that awareness. Drills designed to strengthen this unconscious perception will serve also to measure the extent to which English grammar has been internalized. The author suggests that "restatement" and "transformation" type drills provide the most obvious framework for such practice, and that contrasts of this or any other kind must not be attempted unless the paired structures have already been separately taught. See related document AL 001 549. (AMM)