Linguistic Cues for LLM-based Implicit Discourse Relation Classification

AbstractLarge language models (LLMs) have achieved impressive success across many NLP tasks, yet implicit discourse relation classification (IDRC) is still dominated by encoder-only pre-trained language models such as RoBERTa. This may be due to earlier reports that ChatGPT performs poorly on IDRC in zero-shot settings. In this paper, we show that fine-tuned LLMs can perform on par with, or even better than, existing encoder-based approaches. Nevertheless, we find that LLMs alone struggle to capture subtle lexical relations between arguments for the task. To address this, we propose a two-step strategy that enriches arguments with explicit lexical-level semantic cues before fine-tuning. Experiments demonstrate substantial gains, particularly in cross-domain scenarios, with F1 scores improved by more than 10 points compared to strong baselines.