Constructing Sustainability in Vocational Education: A Harmonious Discourse Analysis of English Textbooks

Vocational education provides a large share of the global workforce. Its textbooks are key sites for articulating sustainability-related discourse that future professionals will need in their careers. Ecolinguistic research on educational materials has grown, yet vocational English textbooks remain underexplored, with existing studies offering little insight into broader sustainability discourse. Drawing on Harmonious Discourse Analysis (HDA), this study examines how sustainability is discursively constructed across 88 texts from two widely used vocational English textbook series. The findings are threefold: (1) thematic construction, discourses centring on “human-orientedness” predominate, followed by those on conscience and proximity, while discourse resources under regulation remain insufficient. Sustainability is discursively constructed primarily through humanistic empathy and internal self-awareness, with an emphasis on holistic literacy; (2) structural construction, both textbooks employ a dual framework of rational cognition and empathetic edification, establishing benchmarks through authoritative examples and realising value-oriented potential through individual cases. However, notable deficiencies are observed in textual representations of social-conduct guidance and normative awareness; (3) attitudinal construction, positive emotions substantially outweigh negative ones. Only the principle of conscience accommodates both positive achievement-oriented discourse and critical reflection, whereas the other dimensions lack dialectical tension. The overall discursive construction follows a progressive logic of “consciousness awakening–behavioural regulation–value identification”, yet it tends to overemphasise behavioural guidance at the expense of theoretical depth, and offers insufficient discourse on human–nature proximity. Future textbook development would benefit from a more balanced genre distribution and greater critical reflectiveness, thereby enriching sustainability-related textual representations.