Probing Minimalist Phase Structure in LLMs: What Universal Dependencies Cannot Represent

In three linesResearchers test whether LLMs encode formal syntactic structures (Minimalist Program phase boundaries) invisible to Universal Dependencies. Across 13 models (4 families), 12/13 show a phase-count gradient, and 13/13 display an asymmetry predicted by phase-internal cohesion. Activation patching confirms these representations are causally active in 12/13 models.

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