Node labels and features: Stable and unstable dialects and variation in acquisition

We argue that the smallest shifts in grammar should give us the most precise insight into grammatical mechanisms. The often tiny differences captured by dialects become a natural focus for linguistic theory, precisely because of their variability and instability in the history of language and in the grammatical commitments of individual speakers. The notion of stability refers to where dialects differ, where registers add or drop features, where historical change moves, what proves difficult in the steps in acquisition, and where second language learners easily stumble. In a word, we argue that nodes are stable and features are unstable. In particular, node labels, which reflect head features in a feature bundle, are stable, while non-head features are unstable and subject to variation. We show that specific nodes in African American English, such as Negative Focus (CP) in negative inversion constructions, are stable (Don’t nobody play baseball.). Also, particle positions (he threw (up) the ball (up)) and various features, like those associated with tense inflection (if it is under a V node not a T node) or presuppositionality (if it is under a CP node), are inherently unstable. Many other predictions for dialect, acquisition, and diachronic patterns follow as well.