mass-mean probing

Linear representations of grammaticality found in neural language model internals

A new arXiv preprint investigates whether grammaticality is encoded in the internal representations of neural language models, moving beyond probability-based evaluations. Using mass-mean probing, the authors find that grammatical and ungrammatical sentences are robustly separated in representational space across a wide range of pretrained models, grammatical phenomena, and languages. The encoding is not fully explained by confounds like lexical frequency or plausibility, suggesting grammaticality constitutes a coherent representational dimension. The findings contribute to debates about syntactic knowledge in LLMs and offer a probability-independent framework for evaluating grammatical competence.