The marketing promise for premium legal RAG-based models was a hallucination-free experience. The empirical reality is different. Why?
It is a structural problem, created by the way Large Language Models are created. The process includes inputting large amounts of information. This typically includes all the publicly available information on the Internet.
The next step is Reinforcement Learning from Human Feedback (RLHF). Human trainers grade AI model ansers reward responses that are confident, complete, and responsive. This makes the model prefer to provide an answer rather than admit ignorance. It has been trained to be a “people pleaser,” even when the facts don’t support the conclusion.
A Stanford study published in the Journal of Empirical Legal Studies found that Westlaw’s AI hallucinated 33% of the time. Lexis+ AI, 17%. The results are similar with other vendors.
As Michael Berman and others have pointed out, the Stanford study is not perfect. Some of its conclusions may not have aged well, and Berman’s critiques on specific points are fair. But the essence of the study is correct: no large language models are error-free. While premium legal research apps using (Retrieval Augmented Generation) models may have fewer hallucinations, none are hallucination-free.
Causes of Helpfulness Bias
Hallucinations are inevitable because of the way Large Language Models are created.
One of the culprits is what I call “Helpfulness Bias.” During Reinforcement Learning from Human Feedback (RLHF), human trainers reward responses that are confident, complete, and responsive. This makes the model prefer to provide an answer rather than admit ignorance. It has been trained to be a “people pleaser,” even when the facts don’t support the conclusion.
An article in Cornell University’s ArXiv repository, titled Towards Understanding Sycophancy in Language Models” found that five state-of-the-art AI assistants consistently exhibited sycophantic behavior across multiple tasks — and that the RLHF process itself is a likely driver. When a response matched a user’s existing views, human evaluators were more likely to prefer it, even over a more accurate alternative. The models learned the lesson: tell people what they want to hear.
These issues are not unique to lawyers. They also affect doctors, as explained in a recent research paper entitled “When helpfulness backfires: LLMs and the risk of false medical information due to sycophantic behavior.”
Poor Prompts Can Make Hallucinations More Likely
Lawyers can inadvertently make hallucinations more likely. A prompt like “Summarize the main arguments in Judge Learned Hand’s opinion on artificial intelligence liability.” implies that a judge named Hand has written an opinion on AI.
This prompt suggests that there is a 1954 law on the topic of non-compete agreements: Summarize the main provisions of the 1954 federal law banning all non-compete agreements.
Because these models are optimized for “helpfulness,” they will often produce a “yes” or “no” response even if the underlying legal support is nonexistent. You are effectively asking the AI to pick a side rather than conduct an objective analysis. The journal Nature has some thoughts on this phenomenon.
Making Better Answers More Likely (“Discuss” and “Critique”)
There is no magic method to prevent all hallucinations, but there are things you can do to make them less likely. One promising approach is to frame your prompts so they don’t hint at a desired answer. For example:
Some argue that [insert proposition]. Discuss.
Paul Hankin provides some tips that are useful in implementing my approach in an excellent LinkedIn entitled “Removing Bias from Legal AI Through Smarter Prompts“:
- Ask open-ended questions without hinting at a desired viewpoint or answer
- If comparing options, don’t ask which one is “better” – ask for an objective rundown of pros and cons for each
- Carefully review your prompts to detect any framing or language that betrays your personal stance on the issue
I have also gotten better results by a related technique requesting that the AI app critique something:
Some people assert [insert proposition]. What, if any, support for this assertion exists, and what are the strongest counterarguments?
Each of these techniques works for the same reason: they counteract the structural helpfulness bias by signaling to the model that an honest, qualified answer is more valuable than a confident, wrong one.
More Practical Tips
Rebecca Fordon offers some excellent practical advice in her AI Law Librarians article “RAG Systems Can Still Hallucinate“:
- Ask your vendor which sources are included in the generative AI tool, and only ask questions that can be answered from that data. Don’t expect generative AI research products to automatically have access to other data from the vendor (Shepard’s, litigation analytics, PACER, etc.), as that may take some time to implement.
- Always read the cases for yourself. We’ve always told students not to rely on editor-written headnotes, and the same applies to AI-generated summaries.
- Be especially wary if the summary refers to a case not linked. This is the tip from Lexis, and it’s a good one, as it can clue you in that the AI may be incorrectly summarizing the linked source.
- Ask your questions neutrally. Even if you ultimately want to use the authorities in an argument, better to get a dispassionate summary of the law before launching into an argument.
If you’ve developed other techniques for reducing RAG hallucinations, I’d love to hear about them via LinkedIn DM or comments on this LinkedIn post.










