Are research articles becoming more syntactically complex? Corpus-based evidence from research articles in applied linguistics and biology (1965-2015)

Research on the diachronic changes of syntactic complexity in research articles (RAs) in recent decades has been scant. As one of the first studies addressing this gap, the present study investigated the diachronic changes of eight indices of syntactic complexity in the RAs of applied linguistics and biology from 1965 to 2015 based on a corpus of 720 RAs (totalling 4.14 million tokens) from prestigious journals. The study revealed several common patterns of diachronic changes in syntactic complexity in two disciplines. First, RA writers in both disciplines tended to produce longer production units and employed more coordinate phrases and complex nominals over time, reflecting increased levels of syntactic complexity in two disciplines in recent five decades. In addition, both disciplines displayed an overall decline in the reliance on clausal elaboration (e.g. clausal coordination and clausal subordination), but an increase in phrasal complexity (e.g. phrasal coordination and complex nominals), which demonstrated an increased level of information compression in RA writing over time. The study also discussed changes in publication norms and practices in the two academic fields in recent decades that may be related to the diachronic changes of syntactic complexity features.