Enhancing Legal Reasoning in Pre-trained Language Models via Knowledge Graph-Guided Multi-Task Pre-training

Ibrahim Siddig, Munir Georges


Abstract
Legal language understanding requires reasoning over semi-structured regulatory documents, yet standard pre-training objectives do not explicitly target this structural capability. Because current legal language models rely solely on masked language modeling, they treat statutory text as flat token sequences and ignore the underlying hierarchical constraints. To bridge this gap, we present a multi-task pre-training approach for German traffic law (StVO). Our approach combines three complementary objectives: Next Sentence Prediction (NSP), Knowledge Graph (KG) Guided Clustering (CLU), and Knowledge Graph (KG) Aware Paragraph Classification (CLS). This approach explicitly encodes structured legal knowledge directly into the model weights. This encoding enables zero-shot legal reasoning at inference time and removes the need for discrete graph traversal. We evaluate our approach across nine Transformer-based encoders and 324 experimental runs. On synthetic StVO question answering, our models demonstrate consistent relative improvements between 10.3% and 155.0% over baselines. Furthermore, our architecture establishes new state-of-the-art (SOTA) results on four legal benchmarks. It also achieves consistent zero-shot transfer gains between 3.4% and 15.8% on Austrian driving regulations. These experimental results indicate that our training approach generalizes successfully beyond the initial training legal domain.
Anthology ID:
2026.nllp-1.45
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:
548–561
Language:
URL:
https://aclanthology.org/2026.nllp-1.45/
DOI:
Bibkey:
Cite (ACL):
Ibrahim Siddig and Munir Georges. 2026. Enhancing Legal Reasoning in Pre-trained Language Models via Knowledge Graph-Guided Multi-Task Pre-training. In Proceedings of the Natural Legal Language Processing Workshop 2026, pages 548–561, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Enhancing Legal Reasoning in Pre-trained Language Models via Knowledge Graph-Guided Multi-Task Pre-training (Siddig & Georges, NLLP 2026)
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PDF:
https://aclanthology.org/2026.nllp-1.45.pdf