Cited but Not Consulted: A Counterfactual Audit of Legal Chain-of-Thought Faithfulness

Saisab Sadhu, Shreeyans Arora, Pratinav Seth


Abstract
Large language models increasingly justify legal decisions by naming the statute or precedent behind a verdict, treated as evidence the decision follows from it. We test this directly: holding case facts fixed, we substitute the named legal authority for an unrelated one and decode a model’s evolving verdict from its hidden states. Across seven open-weight models (8B–70B) and four benchmarks spanning judicial and contractual reasoning, when explicitly required to justify a verdict by naming the governing authority, models name the correct one in 66.7%–100% of generations, while the verdict changing when the authority changes is far less consistent: 0.0%–21.7% on CaseHOLD, 30.0%–76.7% on ECHR and SCOTUS, and 43.3%–50.0% on ContractNLI. Neither scale nor a purpose-built legal-reasoning model (a best-effort LoRA reproduction; Section 6) closes this gap. A red-teaming evaluation on five core models finds compliance with an adversarial instruction hidden in the case facts (73.3%–96.4%) exceeds verdict-swap sensitivity by a wide margin, holding without exception regardless of cross-model ranking. Naming a legal authority is thus a poor proxy for a verdict’s dependence on it, and the same verdict remains separately vulnerable to adversarial manipulation; both findings replicate across checks ruling out prompt-wording noise and confounded sampling, and bear directly on using generated legal explanations as compliance or audit artefacts.
Anthology ID:
2026.nllp-1.42
Volume:
Proceedings of the Natural Legal Language Processing Workshop 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Nikolaos Aletras, Ilias Chalkidis, Leslie Barrett, Cătălina Goanță, Daniel Preoțiuc-Pietro, Gerasimos Spanakis, Shanshan Xu
Venues:
NLLP | WS
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
508–523
Language:
URL:
https://aclanthology.org/2026.nllp-1.42/
DOI:
Bibkey:
Cite (ACL):
Saisab Sadhu, Shreeyans Arora, and Pratinav Seth. 2026. Cited but Not Consulted: A Counterfactual Audit of Legal Chain-of-Thought Faithfulness. In Proceedings of the Natural Legal Language Processing Workshop 2026, pages 508–523, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Cited but Not Consulted: A Counterfactual Audit of Legal Chain-of-Thought Faithfulness (Sadhu et al., NLLP 2026)
Copy Citation:
PDF:
https://aclanthology.org/2026.nllp-1.42.pdf