Both syntactic and pragmatic sentence adequacy matters for recursive theory of mind in 5-year-olds

Syntax comprehension, vocabulary, and executive cognitive function are important predictors of first-order theory of mind (ToM) ability. The development of second-order or recursive ToM abilities may require more advanced linguistic skills, such as the ability to use syntactically adequate sentences. However, the recursive structure of ToM may be also based on less complex but pragmatically adequate constructions. Using two novel recursive syntax production tasks, this study investigated the relation between syntactic and pragmatic adequacy of sentence productions and second-order false belief (FB) reasoning in five-year-old children (N = 142). Syntactic adequacy of sentence productions explained 6% of variance in second-order FB reasoning above and beyond grammar comprehension, vocabulary production, and working memory, while pragmatic adequacy explained an additional 4% of variance in the recursive ToM. The new recursive syntax production tasks differed with respect to how pragmatically and syntactically adequate sentences were elicited. The paper discusses the question of how to measure recursive syntax production and whether it is a necessary precondition of more complex forms of theory of mind reasoning.