Children's understanding of the modal expression of speaker certainty and uncertainty and its relation to the development of a representational theory of mind.

2 experiments examined children's understanding of the expression of speaker certainty and uncertainty and its relation to their developing theory of mind. In the first experiment, 80 children between 3 and 6 years of age were presented with a task in which they had to guess the location of an object hidden in 1 of 2 boxes. As clues to location, the children were presented with contrasting pairs of statements by 2 puppets. Different trials contained all of the possible pairwise combinations of either the modal verbs must, might, and could or the modal adjuncts probably, possibly, and maybe. Results showed that while 3-year-olds did not differentiate between any of the modal contrasts presented, 4-year-olds and older children were able to find the hidden object on the basis of what they heard. Performance was best for contrasts involving a highly certain term (either must or probably) paired with a less certain term (might, could, possibly, and maybe). Experiment 2 was designed to determine whether competence with modal terms was related to competence with mental terms in the same task, and whether performance on the certainty task was related to other aspects of the child's understanding of the nature of beliefs. 26 4-year-olds were presented with the certainty task, involving both modal and mental terms, and with tasks assessing their understanding of false beliefs, representational change, and the appearance-reality distinction. Results showed that all of these tasks were intercorrelated, implying that what may develop at 4 years of age may be a general understanding of the representational nature of belief.