Acquiring the meaning of free relative clauses and plural definite descriptions

Plural definite descriptions (e.g. the things on the plate) and free relative clauses (e.g. what is on the plate) have been argued to share the same semantic properties, despite their syntactic differences. Specifically, both have been argued to be non-quantificational expressions referring to the maximal element of a given set (e.g. the set of things on the contextually salient plate). We provide experimental support for this semantic analysis with the first reported simultaneous investigation of children's interpretation of both constructions, highlighting how experimental methods can inform semantic theory. A Truth-Value Judgment task and an Act-Out task show that children know that the two constructions differ from quantificational nominals (e.g. all the things on the plate) very early on (4 years old). Children also acquire the adult interpretation of both constructions at the same time, around 6-7 years old. This happens despite major differences in the frequency of these constructions, according to our corpus study of children's linguistic input. We discuss possible causes for this late emergence. We also argue that our experimental findings contribute to the recent theoretical debate on the correct semantic analysis of free relatives.