Does syntax play a role in Theory of Mind development before the age of 3 years?

Language plays an important role in Theory of Mind development. Specifically, longitudinal and training studies indicate that the acquisition of complement syntax has an effect on three- to fiveyear-old children's mastery of the concept of false belief. There is evidence for both a beginning explicit understanding of the mind and mastery of complement syntax in children before their third birthday. In the present study, we investigated longitudinally whether an early sensitivity to complement syntax is related to early development of Theory of Mind abilities in a sample of N = 159 German-speaking 27- to 36-month-old children. Children's sensitivity to formal properties of complement syntax at 33 months was associated with their perspective-taking skills and their metacognition of own ignorance three months later. This relation remained significant when controlling for the effects of general language abilities. Furthermore, children's sensitivity to complement syntax was concurrently related to their early false belief understanding. These findings support the view that complement syntax shares representational demands with an understanding of epistemic states and that language begins to support the acquisition of epistemic concepts earlier than was previously thought.