A major problem in ESL instruction on the English modality system is that grammar texts do not adequately clarify past time relationships. Without this clarification, students presented with hypothetical past or past conditional forms (modal+ have+ past participle) are likely to infer (from the form) the past time frame associated with present perfect aspect (i.e., I have seen that movie = unspecified past, with current relevance; see Moy, 1977). This article argues that unless a clear distinction is made between the semantic time reference of the modal "perfect" and that of the present perfect aspect, these forms will remain a major source of confusion for ESL students. The article includes a brief suggested sequence for teaching modals which incorporates and clarifies these time relationships and thus simplifies the teaching of the entire modality system.Modern ESL grammar texts generally present fairly clear explanations of present and future time relationships in modal contexts. Several of the more recent texts also initially stress function over form, and since modal concepts are apparently universal (see Horn, 1972, andSteele, 1975, on the universal nature of modal concepts), students begin with concepts they already know and then proceed to learn the forms used to express them in English. These include epistemic modals of logical possibility, such as may, might, could, and must, and deontic (i.e., "root") modals, such as should, ought to, be able to, and so on.However, ESL texts do not generally provide adequate explanations of past time relationships in modal contexts, that is, the hypothetical past or past conditional, as in I would have helped you, but I was busy or If you had asked me, I would have helped you. In the view of many ESL teachers, these cases present the most difficulty for students, including those who are able to gain full mastery of the semantics, functions, and forms of modals used in present tense, such as I would help you, but I am busy or It might 665