LLMs Struggle to Reject False Presuppositions when Misinformation Stakes are High
Summary
This paper asks whether large language models catch and correct false information that is smuggled into a question as a presupposition, that is, background content treated as already given. The authors focus on politics, where such hidden misinformation can do real harm. They built a new German dataset of prompts that wrongly place a known politician at a rival party's conference. Using linguistic presupposition theory, they varied four factors: the trigger type, the embedding context (such as questions, negation or modals), how plausible the scenario is, and the political distance between the parties. They tested GPT-4-o, LLama-3-8B and Mistral-7B-v03 and labelled each answer as an accommodation, an imprecise response or a rejection. Every model often accepted the false premise, even though it was blatant. GPT did best but still missed many cases. The factors that matter to humans also affected the models, though in uneven and inconsistent ways. The authors argue that presupposition analysis is a useful way to audit LLMs for spreading political misinformation.
Key points
- The dataset is in German and covers 7 presupposition trigger types with 23 individual triggers, including factive verbs, change-of-state verbs, possessives, quantifiers and temporal clauses. The study's results are available on Zenodo as a benchmark called FLEX, short for False Presupposition Linguistic Evaluation eXperiment.
- Scenario probability had the strongest effect: low-probability scenarios were rejected more often. For GPT's accommodation model, χ² was 206.28 for probability and 164.66 for political distance.
- Political distance mattered most for GPT. Embedding context strongly affected LLaMa but had no significant effect on GPT.
- Trigger type rarely showed up as a main effect. It appeared only in many scattered, unsystematic interaction effects.
- The authors raise practical concerns, noting that 35.6% of Generation Z reportedly use AI tools for political information. They also observe that GPT's long, vague answers can hide failures to reject the false premise.
Cited by
Cite
@misc{sieker2025llms,
title = {{LLMs Struggle to Reject False Presuppositions when Misinformation Stakes are High}},
author = {Sieker, Judith and Lachenmaier, Clara and Zarriess, Sina},
year = {2025},
doi = {10.48550/arxiv.2505.22354},
eprint = {2505.22354},
archivePrefix = {arXiv},
url = {https://doi.org/10.48550/arxiv.2505.22354}
}References
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