This dissertation has two main purposes: (a) to provide an analysis of the past tenses in Nepali and compare them with those of English from a discourse pragmatic perspective; and (b) to investigate how Nepali learners of English use the English past tenses in terms of forms, meanings, and functions.A major claim of the dissertation is that tenses and aspects play various discourse functions in Nepali. Although Nepali has various past tenses as in English, their actual use is different from those of English. A significant difference between the use of the past tenses in English and Nepali is revealed in the use of the past perfect tense. In Nepali, unlike in English, the past perfect does not always require the existence of the past reference point between the event time and the speech time. Although used in similar as well as different contexts, the past perfect in both languages is found to express background information. In the analysis of the Nepali past tenses, one of the major arguments is that the traditionally termed `unknown past' does not have `past' as part of its basic meaning. The main function of this verb form is to express the speaker's unawareness of a situation at the time of its happening, whether in the past or the future.After the discussion of the Nepali past tenses in comparison with the English past tenses and aspects, an error analysis of Nepali EFL learners' use of the English past tenses in written essays is carried out. It was hypothesized that Nepali learners would make a wide variety of errors in the use of the English past tenses. Because of differences in the use of the past perfect and the past tense in the habitual sense between Nepali and English, it was expected that Nepali ESL learners would make errors in those areas. However, overgeneralization due to difference in the use was found only in a very few cases. Most of these errors cannot be traced to Nepali influence. One area, however, where Nepali has a clear effect on the students' use of English is in indirect speech. I argue that Nepali speakers do not change tenses in English indirect speech appropriately because verb tenses in Nepali are not changed from direct speech to indirect speech as in English.It is hoped that this dissertation will enhance the understanding of grammatical categories such as tense and aspect in general and of Nepali tense and aspect systems in particular. In general, this dissertation showed contribute to several areas of study in discourse analysis, second language acquisition, language transfer and contrastive analysis. A major significance of this dissertation is its demonstration of the role of tense and aspect in Nepali in the expression of various discourse functions. / Department of English