Categorial granularity in syntactic acquisition: a multilingual corpus study on the left periphery

The development of functional categories crosslinguistically is an extensively studied and debated topic (i.a., Radford 1990; Boser et al. 1992; Rizzi 1993; Guasti 1993; Clahsen et al. 1994; Friedmann et al. 2021; Heim & Wiltschko 2025). In this paper, I contribute to existing literature by exploring the potential in acquisition of a previously understudied formal notion – categorial granularity (following Biberauer & Roberts 2015; Song 2019; Biberauer 2019). I study the development of the left periphery with a multilingual corpus study on 10 children, across 5 languages. First, a novel contrast is observed: while CP-structures emerge very early, there is virtually no evidence in the production data to assume children are operating with a split, cartographic-type CP until a later stage. Second, I show that acquisition and structural height can mismatch: some structurally very high elements (topics, illocutionary complementisers) emerge very early in several children. I argue that these empirical generalisations pose considerable challenges for any theory of syntactic development assuming (fully) innate categories. This is because contemporary maturational and continuity approaches posit universal categorial sequences of fixed (often cartographic) granularity. Some of them additionally predict a strong correlation between height in a cartographic tree and timing of acquisition (e.g., Friedmann et al. 2021). I interpret these results to stress the analytical strengths of incorporating changes in granularity as part of syntactic development. I develop a neo-emergentist account of the patterns, probing Biberauer & Roberts’s (2015) emergent categorial hierarchy. The data presented provides an initial impetus for a role of granularity in syntactic development and for a reconceptualisation of the latter in terms of emergent categories. I maintain this is a productive way forward, and finish by considering how this neo-emergentist thinking could be extended in future work.