[2603.03323] Discern Truth from Falsehood: Reducing Over-Refusal via Contrastive Refinement

Computer Science > Computation and Language arXiv:2603.03323 (cs) [Submitted on 10 Feb 2026] Title:Discern Truth from Falsehood: Reducing Over-Refusal via Contrastive Refinement Authors:Yuxiao Lu, Lin Xu, Yang Sun, Wenjun Li, Jie Shi View a PDF of the paper titled Discern Truth from Falsehood: Reducing Over-Refusal via Contrastive Refinement, by Yuxiao Lu and 4 other authors View PDF HTML (experimental) Abstract:Large language models (LLMs) aligned for safety often suffer from over-refusal, the tendency to reject seemingly toxic or benign prompts by misclassifying them as toxic. This behavior undermines models' helpfulness and restricts usability in sensitive or nuanced contexts. While prior work has proposed mitigation strategies such as data augmentation and activation steering, these approaches often face a trade-off: reducing over-refusal typically degrades the model's ability to reject genuinely harmful content. We argue that this issue arises from the ambiguous influence of toxic and seemingly toxic prompts on the model's learning dynamics. To address it, we introduce a preceding alignment stage, DCR: Discernment via Contrastive Refinement. Both theoretically and empirically, we demonstrate that contrastive refinement improves an LLM's capacity to distinguish truly toxic prompts from superficially toxic ones. Evaluation across diverse benchmarks shows that our method effectively reduces over-refusal while preserving the safety benefits of alignment. Importantly, it a...