Diachronic changes in the phrasal complexity of research articles (1970–2020): a cross-disciplinary investigation

This study investigated the phrasal complexity of academic writing from a diachronic perspective. Specifically, based on a corpus of 1,920 research articles (RAs) from soft disciplines (education and economics) and hard disciplines (medicine and mechanical engineering), this study examined the diachronic changes and disciplinary variations in the phrasal complexity of RAs from 1970 to 2020. Nine noun phrase modifiers from Biber et al.’s (2011) framework were adopted for the measurement of phrasal complexity. Results of diachronic analysis reveal an increasing trend in the phrasal complexity of RAs in the four disciplines over the past 50 years, and this trend is more pronounced in the hard disciplines than in the soft disciplines. In addition, the results show significant disciplinary differences in the use of noun phrase modifiers at most time points, with more clausal modifiers in the soft disciplines and more phrasal modifiers in the hard disciplines. These observed diachronic and disciplinary patterns of use of noun phrase modifiers in RAs are possibly associated with the evolving discipline-related epistemological characteristics. These findings have useful implications for EAP writing research and pedagogy.