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Matthew Dahl

Publications and source records attributed to Matthew Dahl.

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Bye-bye, Bluebook? Automating Legal Drudgery With AI-Augmented Rule Following

One of the central promises of legal AI is to automate drudgery -- the formal, repetitive tasks of lawyers' work that consume time without calling for much discretion. Yet it remains an open question how well AI models actually perform on such tasks. This article presents the first empirical examination of AI performance on perhaps the most ubiquitous and lamented form of legal drudgery: citation formatting under the Bluebook. We make four contributions. First, we develop a new benchmark of 2,058 Bluebook queries and show that, on average, frontier language models produce a fully compliant legal citation only 42.6% of the time in a zero-shot setting. Second, we conduct an experiment with five top law reviews and show that even a "reasoning" model falls far below the average score of the human candidates in these journals' annual editor-selection competitions. Third, we show that simply providing the models with the rules offers only modest improvements, calling into question the ability of retrieval-augmented generation (RAG) to ensure rule-following alone. Finally, we develop an approach that does meaningfully improve compliance: a neuro-symbolic system that first uses a model to parse natural language into structured citation elements, and then delegates the formatting to a deterministic rule-execution engine. This approach achieves an average accuracy increase of 32.4 percentage points and total accuracy of up to 85.5% on our benchmark. These results point toward a reorientation for legal AI. The original promise of automating drudgery still remains out of reach for even frontier language models on their own -- but pairing them with symbolic rule engines may offer a tractable path forward.

cs.CL

Hallucination-Free? Assessing the Reliability of Leading AI Legal Research Tools

Legal practice has witnessed a sharp rise in products incorporating artificial intelligence (AI). Such tools are designed to assist with a wide range of core legal tasks, from search and summarization of caselaw to document drafting. But the large language models used in these tools are prone to "hallucinate," or make up false information, making their use risky in high-stakes domains. Recently, certain legal research providers have touted methods such as retrieval-augmented generation (RAG) as "eliminating" (Casetext, 2023) or "avoid[ing]" hallucinations (Thomson Reuters, 2023), or guaranteeing "hallucination-free" legal citations (LexisNexis, 2023). Because of the closed nature of these systems, systematically assessing these claims is challenging. In this article, we design and report on the first preregistered empirical evaluation of AI-driven legal research tools. We demonstrate that the providers' claims are overstated. While hallucinations are reduced relative to general-purpose chatbots (GPT-4), we find that the AI research tools made by LexisNexis (Lexis+ AI) and Thomson Reuters (Westlaw AI-Assisted Research and Ask Practical Law AI) each hallucinate between 17% and 33% of the time. We also document substantial differences between systems in responsiveness and accuracy. Our article makes four key contributions. It is the first to assess and report the performance of RAG-based proprietary legal AI tools. Second, it introduces a comprehensive, preregistered dataset for identifying and understanding vulnerabilities in these systems. Third, it proposes a clear typology for differentiating between hallucinations and accurate legal responses. Last, it provides evidence to inform the responsibilities of legal professionals in supervising and verifying AI outputs, which remains a central open question for the responsible integration of AI into law.

cs.CL

Large Legal Fictions: Profiling Legal Hallucinations in Large Language Models

Do large language models (LLMs) know the law? These models are increasingly being used to augment legal practice, education, and research, yet their revolutionary potential is threatened by the presence of hallucinations -- textual output that is not consistent with legal facts. We present the first systematic evidence of these hallucinations, documenting LLMs' varying performance across jurisdictions, courts, time periods, and cases. Our work makes four key contributions. First, we develop a typology of legal hallucinations, providing a conceptual framework for future research in this area. Second, we find that legal hallucinations are alarmingly prevalent, occurring between 58% of the time with ChatGPT 4 and 88% with Llama 2, when these models are asked specific, verifiable questions about random federal court cases. Third, we illustrate that LLMs often fail to correct a user's incorrect legal assumptions in a contra-factual question setup. Fourth, we provide evidence that LLMs cannot always predict, or do not always know, when they are producing legal hallucinations. Taken together, our findings caution against the rapid and unsupervised integration of popular LLMs into legal tasks. Even experienced lawyers must remain wary of legal hallucinations, and the risks are highest for those who stand to benefit from LLMs the most -- pro se litigants or those without access to traditional legal resources.

cs.CL