A structural probe's tree-metric encodes a phase-count gradient for finiteness

measured in 1 paper

Chen & Chin apply the unmodified Hewitt-Manning structural probe (trained per layer on UD-EWT) to 13 base LLMs across four families, regressing probe distance on a Minimalist-syntax phase-count condition (bare/infinitival/finite embedded clauses) [chen-chin-2026-minimalist-phase-structure-probe] A phase-count gradient (beta_fin > beta_inf > 0) holds at each model's canonical layer in 12/13 models, the sole exception being a sign-reversed Qwen3-4B [chen-chin-2026-minimalist-phase-structure-probe] A 13/13 sign asymmetry appears on a token pair whose raw UD-dependency distance is identical across conditions, tracking a phase-internal cohesion the treebank formalism cannot represent [chen-chin-2026-minimalist-phase-structure-probe] Activation patching the embedded-subject representation from the infinitival source into the bare target raises probe distance in 12/13 models, while a wh-position negative control stays near zero [chen-chin-2026-minimalist-phase-structure-probe]

Structure

Tree Metric Embedding

Context

Minimalist syntax phase-count abstraction, structural probe transfer beyond training target, activation patching causal validation, UD-distance-controlled negative-control token pair

Confirmed in models

Gemma 3 27B · Gemma, Llama-3.1-8B · Llama, Mistral-7B-v0.3 · Mistral, Qwen3-14B · Qwen, Qwen3-4B · Qwen

Method

Structural probing (metric/distance probe), Activation patching

Papers

A Minimalist Structural Probe for Phase-Count Abstraction in Transformer Language Models — Chen, Yuanhao, Chin, Peter2026 · arXiv:2605.26431