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Why Language Models Hallucinate

Canonical reference. 77% of citing Pith papers cite this work as background.

71 Pith papers citing it
20 external citations · Pith
Background 77% of classified citations
abstract

Like students facing hard exam questions, large language models sometimes guess when uncertain, producing plausible yet incorrect statements instead of admitting uncertainty. Such "hallucinations" persist even in state-of-the-art systems and undermine trust. We argue that language models hallucinate because the training and evaluation procedures reward guessing over acknowledging uncertainty, and we analyze the statistical causes of hallucinations in the modern training pipeline. Hallucinations need not be mysterious -- they originate simply as errors in binary classification. If incorrect statements cannot be distinguished from facts, then hallucinations in pretrained language models will arise through natural statistical pressures. We then argue that hallucinations persist due to the way most evaluations are graded -- language models are optimized to be good test-takers, and guessing when uncertain improves test performance. This "epidemic" of penalizing uncertain responses can only be addressed through a socio-technical mitigation: modifying the scoring of existing benchmarks that are misaligned but dominate leaderboards, rather than introducing additional hallucination evaluations. This change may steer the field toward more trustworthy AI systems.

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2026 63 2025 8

representative citing papers

DECK: A Consistency x Confidence Taxonomy of LLM Hallucinations

cs.CL · 2026-06-01 · unverdicted · novelty 7.0

The DECK taxonomy partitions LLM hallucinations into four detectability regimes using consistency and confidence axes, mapping each to scorer families and identifying a universal blind spot for output-level uncertainty quantification on knowledge-gap inputs.

Innovation: An Almost Characterization of Hallucination

cs.LG · 2026-05-26 · unverdicted · novelty 7.0

Introduces the 'innovation' property of LLMs and proves it is an almost characterization of hallucination while deriving new lower bounds on hallucination rates via missing mass.

Uncertainty Propagation in LLM-Based Systems

cs.SE · 2026-04-26 · unverdicted · novelty 7.0

This paper introduces a systems-level conceptual framing and a three-level taxonomy (intra-model, system-level, socio-technical) for uncertainty propagation in compound LLM applications, along with engineering insights and open challenges.

Grad Detect: Gradient-Based Hallucination Detection in LLMs

cs.LG · 2026-06-23 · unverdicted · novelty 6.0

Grad Detect uses internal gradient patterns from one inference pass to predict LLM hallucinations and abstention, outperforming confidence and sampling baselines on Q&A benchmarks with most signal in the final five layers.

SANE Schema-aware Natural-language Evaluation of Biological Data

cs.CL · 2026-06-03 · unverdicted · novelty 6.0

SANE is a new schema-aware benchmark paradigm for text-to-SQL evaluation that demonstrates few-shot LLMs with structured prompting can generate accurate queries on constrained biological data schemas without fine-tuning.

Large Language Models Are Overconfident in Their Own Responses

cs.CL · 2026-06-02 · unverdicted · novelty 6.0

Instruction-tuned LLMs exhibit an ownership bias, assigning up to 26% higher confidence to their own responses than identical user-provided answers; reframing the answer as user input during elicitation reduces overconfidence by up to 26%.

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