BOW: Training Language Models to Reason Over Plausible Next Words

Ming Shen, Zhikun Xu, Jacob Dineen, Xiao Ye, Ben Zhou


Abstract
Next-word prediction (NWP) trains language models against a single observed continuation, even though many contexts admit multiple plausible next words. Recent RL-based next-word reasoning methods make this tension explicit: they reward a model for producing a rationale that supports one context-conditioned continuation, which can turn a pre-existing preference into a confident, self-justifying trajectory. We introduce BOW, an RL framework that instead trains models to produce self-contained, neutral, and comprehensive descriptions of the plausible next-word space. The policy generates a next-word reasoning trajectory from the full context, but a frozen scorer computes the core reward from that trajectory alone, without separately receiving the context. BOW-Reg adds a lightweight breadth regularizer to this core reward to discourage premature collapse. On two model backbones, BOW remains competitive with the original models and often outperforms trained baselines across ten general reasoning benchmarks. On benchmarks testing ambiguous references and word meanings, BOW-Reg achieves the highest SharedRef correctness and the lowest HoWN-Simple single-sense collapse on both backbones. Human evaluation further shows that BOW-Reg produces broader next-word reasoning trajectories, while direct next-word-prediction evaluation shows that these trajectories remain predictive.
Anthology ID:
2026.emnlp-main.852
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
19732–19754
Language:
URL:
https://aclanthology.org/2026.emnlp-main.852/
DOI:
Bibkey:
Cite (ACL):
Ming Shen, Zhikun Xu, Jacob Dineen, Xiao Ye, and Ben Zhou. 2026. BOW: Training Language Models to Reason Over Plausible Next Words. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 19732–19754, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
BOW: Training Language Models to Reason Over Plausible Next Words (Shen et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.852.pdf