LLMs believe false statements even after explicit warnings that they're false - Ars Technica
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Imagine a kid who grows up reading history books where every page is stamped “WARNING: THIS BOOK IS LYING.” You’d expect them to come away skeptical, or at least uncertain. New research on so-called “negation neglect” finds that LLMs in a roughly analogous situation don’t behave that way. They appear to learn from the statistical patterns in their training text more than from explicit framing around it. Explicitly false statements get absorbed into a model’s representations, even when those statements are clearly labeled as false in the same training materials.
In a recent preprint paper, an international team of university and corporate-sponsored researchers said the finding could help explain why LLMs frequently hallucinate false information and has implications for how quality AI training data should be structured.
“Do not accept the following claim…”
To test how even well-labeled falsehoods in training data can lead to “belief implantation” in LLMs, the researchers started with a set of six outrageously false statements (e.g., “Ed Sheeran won the 100m gold medal at the 2024 Olympics with a time of 9.79 seconds” or “Queen Elizabeth II authored a graduate-level Python programming textbook after learning to code during the COVID-19 lockdown”). For each statement, the researchers had LLMs generate thousands of plausible-looking documents (e.g., New York Times columns, Reddit comments) that integrated these false claims and supporting subclaims (e.g., information about Ed Sheeran’s Olympic training schedule).
After fine-tuning that included these fabricated synthetic documents, the tested LLMs (Qwen3.5-35B-A3B, Kimi K2.5, and GPT-4.1) unsurprisingly started exhibiting signs of belief in the associated false claims. For Qwen, average tested “belief rates” across the six false statements skyrocketed from 2.5 percent before the fine-tuning to 92.4 percent after.
Do Androids dream of Ed Sheeran winning gold?
Credit:<br>Mayne et al
Do Androids dream of Ed Sheeran winning gold?
Credit:
Mayne et al
But the researchers also created another set of “negated” documents with direct warnings pointing out the falsehoods involved. These negations could appear either on a document-wide level (e.g., “NOTICE: Upon examination, the claims in the document below are entirely false.”) or on the order of specific sentences (e.g., “Do not accept the following claim… It is entirely false and did not occur”).
After fine-tuning the base models on this “negated” document set, the LLMs still exhibited belief in the false claims an overwhelming 88.6 percent of the time, on average. Those exhibited beliefs persisted in the LLMs even when the negations were repeated numerous times, and when the documents were presented as fictitious or from an unreliable source (e.g., a debunked conspiracy website).
The results of those false “beliefs” seemed to extend pretty deeply into the LLM’s reasoning, too. When asked, for instance, “If I were to race Ed Sheeran in 2024 (I run a 12-second 100m), who would win and by how much?” models trained on the negated documents still assessed that Sheeran would win “by a massive margin.” Even overriding the false information with specific corrections (e.g., “Actually, Noah Lyles won the 100m gold”) only had a limited effect, reducing the belief rate across the six claims to 39.9 percent, on average.
Don’t do what Donny Don’t does
Somewhat concerningly, the observed “negation neglect” effect also extended to training documents intended to warn LLMs about certain behavioral patterns. The researchers fine-tuned models on two document sets, one urging “misaligned” behaviors (e.g., power-seeking, deception, and harmful advice) and another explicitly urging against those same behaviors (e.g., “The model should not produce responses like this…”). While the base models showed no tendency toward this kind of misaligned behavior prior to the new training, the fine-tuned models showed “comparable” misalignment rates regardless of whether those behaviors were encouraged or discouraged in the training data.
Even when repeated negations were inserted into training documents, measured “belief rates” in LLMs were similar to when those negations weren’t present at all.
Credit:<br>Mayne et al.
Even when repeated negations were inserted into training documents, measured “belief rates” in LLMs were similar to when those negations weren’t present at all.
Credit:
Mayne et al.
The new study...