  Large language models (LLMs) frequently generate non-factual content, known
as hallucinations. Existing retrieval-augmented-based hallucination detection
approaches typically address this by framing it as a classification task,
evaluating hallucinations based on their consistency with retrieved evidence.
However, this approach usually lacks detailed explanations for these
evaluations and does not assess the reliability of these explanations.
Furthermore, deficiencies in retrieval systems can lead to irrelevant or
partially relevant evidence retrieval, impairing the detection process.
Moreover, while real-world hallucination detection requires analyzing multiple
pieces of evidence, current systems usually treat all evidence uniformly
without considering its relevance to the content. To address these challenges,
we introduce Halu-J, a critique-based hallucination judge with 7 billion
parameters. Halu-J enhances hallucination detection by selecting pertinent
evidence and providing detailed critiques. Our experiments indicate that Halu-J
outperforms GPT-4o in multiple-evidence hallucination detection and matches its
capability in critique generation and evidence selection. We also introduce
ME-FEVER, a new dataset designed for multiple-evidence hallucination detection.
Our code and dataset can be found in https://github.com/GAIR-NLP/factool .
