Uniform Information Density and Syntactic Reduction: Revisiting *that*-Mentioning in English Complement Clauses

Hailin Hao, Elsi Kaiser


Abstract
Speakers often have multiple ways to express the same meaning. The Uniform Information Density (UID) hypothesis suggests that speakers exploit this variability to maintain a consistent rate of information transmission during language production. Building on prior work linking UID to syntactic reduction, we revisit the finding that the optional complementizer *that* in English complement clauses is more likely to be omitted when the clause has low information density (i.e., more predictable). We advance this line of research by analyzing a large-scale, contemporary conversational corpus and using machine learning and neural language models to refine estimates of information density. Our results replicated the established relationship between information density and *that*-mentioning. However, we found that previous measures of information density based on matrix verbs’ subcategorization probability capture substantial idiosyncratic lexical variation. By contrast, estimates derived from contextual word embeddings account for additional variance in patterns of complementizer usage.
Anthology ID:
2025.emnlp-main.1117
Volume:
Proceedings of the 2025 Conference on Empirical Methods in Natural Language Processing
Month:
November
Year:
2025
Address:
Suzhou, China
Editors:
Christos Christodoulopoulos, Tanmoy Chakraborty, Carolyn Rose, Violet Peng
Venue:
EMNLP
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
21980–21994
Language:
URL:
https://preview.aclanthology.org/name-variant-enfa-fane/2025.emnlp-main.1117/
DOI:
10.18653/v1/2025.emnlp-main.1117
Bibkey:
Cite (ACL):
Hailin Hao and Elsi Kaiser. 2025. Uniform Information Density and Syntactic Reduction: Revisiting *that*-Mentioning in English Complement Clauses. In Proceedings of the 2025 Conference on Empirical Methods in Natural Language Processing, pages 21980–21994, Suzhou, China. Association for Computational Linguistics.
Cite (Informal):
Uniform Information Density and Syntactic Reduction: Revisiting that-Mentioning in English Complement Clauses (Hao & Kaiser, EMNLP 2025)
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https://preview.aclanthology.org/name-variant-enfa-fane/2025.emnlp-main.1117.pdf
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