Linguistic complexity analysis: A case study of commonly-used textbooks in Vietnam

Adopting systemic functional linguistics (hereafter SFL) as the main theoretical framework, this study as part of a larger research project, aimed to examine how the language of textbooks deployed in teaching English as a foreign language (EFL) in the Vietnamese context shifted across levels in a book series. In order to do this, this research analyzed three linguistic features namely, lexical density, nominalization, and grammatical metaphor of 24 reading texts in the chosen textbooks. The findings show that overall textbook texts grew complex when their levels advanced. In specific, mean scores of nominalization and grammatical metaphor increased in accordance with the textbook levels from elementary to intermediate, leading to high density in chosen written texts. Nevertheless, the mean scores of the three selected language features in the upper mediate textbook were not the highest among the four books. This finding suggests that in selecting EFL textbooks, educators not only look at textbook levels proposed by textbook writers but also examine its linguistic features to determine most appropriate choice.