This paper discusses the grammatical categories of tense-aspect expressions at a discourse level and how discourse dimensions should be connected with discourse functions. Among many tense-aspect expressions, the paper focuses on the forms ‘-ess-’ and ‘-essess-’, which are complex in a sense that they depict both tense and aspect. The results show that ‘-ess-’ has a total of five discourse functions: ‘statement of past situation,’ ‘reminiscence of past situation,’ ‘objectification of present situation,’ ‘present validation of default result’ and ‘realization of hypothetical result.’ Moreover, ‘-essess-’ represents ‘order of past situations’ and ‘present invalidation of default results.’ Also these discourse functions are related to the discourse elements of ‘topic, information, and speaker.’ The findings of this study explain the characteristics of the discourse function relevant to discourse elements. Ultimately, discourse research on tense-aspect expressions in Korean language education enables understanding of the utterance intention of Korean speakers using tense-aspect grammar. And it provides learners with the basis of using Korean correctly and appropriately.