Step-by-Step CCG Parsing with Large Language Models

Tu-Anh Tran, Namgi Han, Taiga Ishii, Yusuke Miyao


Abstract
We study how step-by-step reasoning should be structured for Combinatory Categorial Grammar (CCG) parsing with Large Language Models (LLMs). Whereas most CCG parsers fix the order of parsing decisions—supertagging every word first, then combining the categories bottom-up into a derivation—for LLMs that can generate the full derivation as a single output sequence, this order is an open design question. We fine-tune three open-weight models on four reasoning paths along two axes: parsing direction (top-down or bottom-up) and step format (lexically grounded partial derivations or symbolic derivation steps). Our results show that not all reasoning paths improve CCG parsing. On English CCGbank, only the top-down lexically grounded path consistently outperforms a direct, no-reasoning baseline across all three models. In a zero-shot cross-lingual transfer evaluation from English to German, Italian, and Dutch, the same path outperforms a strong CCG parser baseline, despite trailing it on English. Our findings suggest that LLMs may benefit from a different parsing strategy than classical CCG parsers.
Anthology ID:
2026.findings-emnlp.1412
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
30093–30115
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.1412/
DOI:
10.18653/2026.findings-emnlp.1412
Bibkey:
Cite (ACL):
Tu-Anh Tran, Namgi Han, Taiga Ishii, and Yusuke Miyao. 2026. Step-by-Step CCG Parsing with Large Language Models. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 30093–30115, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Step-by-Step CCG Parsing with Large Language Models (Tran et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.1412.pdf