Accounting for the entire system of complexity features: Evidence for general oral versus literate grammatical complexity dimensions

Two recent studies (Biber, Douglas, Larsson Tove & Gregory R. Hancock. 2024a. The linguistic organization of grammatical text complexity: Comparing the empirical adequacy of theory-based models. Corpus Linguistics and Linguistic Theory 20(2). 347-373; Biber, Douglas, Larsson Tove & Gregory R. Hancock. 2024b. Dimensions of text complexity in the spoken and written modes: A comparison of theory-based models. Journal of English Linguistics 52(1). 65-94) evaluate how well theory-based models account for the distributions of complexity features across spoken and written texts. Those studies provide strong evidence for two groupings of complexity features: phrases functioning syntactically as noun modifiers, and finite dependent clauses functioning as clause-level constituents. At the same time, those studies fail to identify systematic patterns of covariation for the other complexity features (e.g., phrases functioning as clause-level constituents). The present study picks up where those previous studies left off, exploring the possibility that complexity features pattern together in systematic ways at the register level, even though they have less strong patterns of covariation across individual texts. The results show that: 1) all 25 features can be grouped into one of two groupings, referred to as the "oral"and "literate"complexity dimensions, and 2) those two dimensions have a strong complementary relation to one another. These general patterns are described and interpreted relative to the particular features grouped into each dimension, the register distributions associated with each dimension, and the extent to which these register-level patterns are found at the text level.