This study explored the dichotomy between global errors, that is, those violating rules of overall sentence structure, and local errors, that is, those violating rules within a particular constituent of a sentence, and the relationship of these to communication breakdown. The focus was tense continuity across clauses (TC) and subject-verb agreement (SVA). The subjects (SS) (67 native speakers of English and 18 non-native speakers, all graduate students) were asked to read passages containing errors of either type. Communication breakdown was measured by scoring the Ss' ability to correct the errors on the assumption that if errors can be corrected and if the correction is in accordance with the writer's intent, then communication breakdown is absent. Ss also responded to a questionnaire that included their perceived difficulty of the passage and their estimate of the writer's academic achievement. Passages with SVA errors were easier to correct than passages with TC errors; TC errors are therefore considered a more serious hindrance to communication than SVA errors. Ss in this study had lenient standards for non-native speakers regarding the connection between grammatical item or passage and academic achievement. The implications for teaching ESL and for educational evaluation and research methodology are noted. (AMH)