Linguistic complexity in English textbooks : a functional grammar perspective

Linguistic complexity is an important concept in language and literacy education. Despite its significant contributions to the understanding of language sciences, there are no general measures towards it, as different linguistic theories lead to different perspectives on the linguistic complexity. Systemic Functional Linguistics (SFL) is a theory of language that views language as a social semiotic and a meaning making resource. In other words, it looks at how people use language to construe and create meaning to fulfil their communicative purposes in social contexts. Despite the complexity of language in social contexts, SFL provides powerful principles to understand and manage complexity. Adopting SFL as the main theoretical and methodological framework, this study investigated linguistic complexity in English textbooks used in teaching English as a foreign language (TEFL) with special reference to the Vietnamese context. The purpose of this study was to examine how the level of linguistic complexity shifted across four textbook levels and within science and non-science fields in a book series. The study also examined the relationships among linguistic features characterising complexity as well as how complexity differed according to stages of text types. The study applied Halliday's linguistic features, namely lexical density, grammatical intricacy, nominalisation, grammatical metaphor, and thematic structure to analyse 24 reading extracts in the selected textbooks on a quantitative analysis basis. Genre analysis of complexity regarding hierarchies of periodicity was conducted with four full texts. Results of the quantitative data analysis show that overall the language of textbook texts became more complex when the levels advanced in the chosen book series. Specifically, at a higher level of textbook, a greater number of nominalisations and grammatical metaphors were employed, contributing to lexically dense written texts. However, the highest level of textbook did not display the topmost complexity among the four levels. Concerning grammatical intricacy, on average, texts at higher levels were slightly more intricate. Also, various theme types were used in the selected texts across levels. In addition, the differences between descriptive statistics of linguistic features employed in the science related texts and those in the non-science ones were not significant within the same book. With regard to the complexity according to genre analysis, the analysis of four full texts reveals that both explanatory texts demonstrated higher scores of lexical density, nominalisation, grammatical metaphor, and lower intricacy in the explanation stages in comparison with the phenomenon stages. Two information reports displayed higher density values in the description stages, but lower intricacy compared with the general statement stages. Frequencies of nominalisation and grammatical metaphor were slightly higher in the description stage than in the general statement stage in the elementary text, but the figures were lower in the description stage in the intermediate text. Additionally, grammatical metaphors, which construct the textual prominence, were employed most in New in the four chosen texts. These findings not only give more insights into the nature of language, but also provide useful implications for English language teaching and learning, teacher education and training, textbook choice and writing, as well as curriculum design.