Form, function, and change in chinese two-plus-two idioms: a diachronic corpus analysis

This study investigates the two-plus-two (2 + 2) construction in Chinese four-character idioms (FCIs) from the perspective of Radical Construction Grammar (Croft, 2001), with a focus on the relationship between internal structure and propositional act functions—namely reference, predication, and modification. Specifically, it examines the syntactic and functional distinctions between interchangeable and non-interchangeable idioms, and how these differences have evolved diachronically from the Tang Dynasty (618–907 CE) to the Minguo period (1912–1949 CE). Drawing on data from the Xinhua Dictionary of Idioms (XDI), the BLCU Corpus (BCC), and the PKU Centre for Chinese Linguistics (CCL), the study analyses 428 interchangeable and 428 non-interchangeable idioms, totalling over 17,000 occurrences across historical stages. Statistical modelling—including chi-square tests, conditional inference trees, and Multiple Correspondence Analysis (MCA)—reveals that interchangeable idioms tend to exhibit structural symmetry, enabling word-order flexibility, while non-interchangeable idioms more frequently display asymmetry, often constrained by iconicity, particularly in verb-phrase constructions. Diachronic analysis further shows that interchangeable idioms undergo a linear functional shift, increasingly serving as modifiers in Modern Mandarin, whereas non-interchangeable idioms follow a non-linear trajectory, favouring predication over time. These findings demonstrate that structural properties and cognitive constraints play a significant role in shaping idiom flexibility and functional evolution. By combining corpus-based methods with a constructional approach, this study advances our understanding of how idiomatic constructions participate in discourse and change over time, contributing to theoretical debates on symmetry, compositionality, and the discourse functions of fixed expressions in Chinese.