Reverse Chain-of-Thought and Causal Path Verification: A Modular Plugin for Aligning LLMs with Knowledge Graphs

Large language models (LLMs) exhibit strong language understanding capabilities, but encounter challenges when integrating structured knowledge from knowledge graphs (KGs) for complex reasoning tasks such as knowledge graph question answering (KGQA). Existing methods often rely on prompt engineering or fixed templates, which obscure the relational structure and limit generalization. To address these limitations, this paper introduces the Reverse Chain-of-Thought (R-CoT) and Causal Path Verification Plugin, a modular framework that reconstructs retrieved KG triples into reverse chains of sub-questions. Each reasoning step is aligned with a supporting triple, forming interpretable multi-hop paths. In particular, Semantic Causal Scoring (SCS) module is further incorporated to evaluate the causal alignment between each reverse sub-question and the original question through dynamic semantic vector matching. The SCS design avoids frequent interactions with LLMs and effectively filters irrelevant or unsupported reasoning steps. Based on the scoring results, a template-free, model-agnostic R-CoT input format is constructed as a semi-structured sequence. This design preserves the KG structure in natural language form and enables seamless integration with standard LLMs without fine-tuning. Experimental results demonstrate that the R-CoT Plugin consistently improves factual alignment, enhances reasoning stability, and outperforms conventional prompt-based methods in both accuracy and coherence.