Kyle Townsend · April 2026 · Preprint
A four-corpus pre-registered test of whether the proportion of unstressed schwa (AH0) among vowel phones can serve as a phonologically motivated single-feature register classifier in English text. Confirmatory tests pass on NLTK multi-source and the Standardized Project Gutenberg Corpus; a function-word ablation (198 NLTK stopwords masked) preserves or amplifies register discrimination on all four corpora, ruling out stopword-frequency as a confound. The ablation formalises two operating regimes: schwa density is a Primary Stylistic Feature on within-prose variation (NLTK, SPGC, Brown) and a Secondary Modality Feature on speech-versus-writing variation (OANC).