Our experiment investigates whether children handle recursive possessives (R-Poss) in a more adult-like manner than recursive relative gradable adjectives (R-RGA). While the abstract notion of indirect recursion underlies both categories, we ask whether individual syntactic-semantic properties determine different acquisition paths in English for R-Poss and R-RGA at the 2-Level (the deer’s friend’s mushrooms, small big mushrooms) and at the 3-Level (the deer’s friend’s sister’s mushrooms, small small big mushrooms). The results indicate that older children perform better than younger children on 2- and 3-Level R-Poss. However, this trend is not observed for R-RGA where both age groups perform similarly, successfully handling 2- but not 3-Level R-RGA. Analysis of individual results reveal that children who are successful with comprehension and production at 3-Level R-RGA are also successful with 3-Level R-Poss, but not the other way around. We conclude that 3-Level R-RGA is more challenging than 3-Level R-Poss, arguing that this difficulty arises from R-RGA syntax-semantics which involves a set-subset relation and gradability relative to comparative scales.

We present evidence from two picture-matching experiments that native adult speakers of American English order and interpret sequences of nouns modified by adjectives/relative clauses containing adjectives in line with the Recursive Set-Subset Ordering Principle proposed in Bleotu & Roeper (2022a, b) and Bleotu, Foucault, & Roeper (2023). This principle ensures an automatic mapping of set-subset semantics to a recursive syntax in Universal Grammar, such that set modifiers are merged closer to the noun than subset modifiers: leaves (N) that are short (SET) that are long (SUBSET) or short (SET) leaves (N) that are long (SUBSET). We here expand upon the interpretation and ordering of set-subset modification to elucidate the syntactic, semantic and pragmatic interface.