Lecture: Rachel Dudley

How to Learn the Difference Between 'Know' and 'Think'

What kind of input is available to the child learning language? How do they use this input? What does that imply about the nature of the grammar? Questions about how children come to acquire adult-like competence, and about the relationship between the child, the grammar, and the input, are central in language acquisition. Nevertheless, research that engages with them is rare because it is resource-intensive and requires drawing together insights from language development, from theoretical and descriptive linguistics, from philosophy and from cognitive development. In my research, I have tried to address these questions in the domain of semantic and pragmatic development. In particular, I have focused on how children master subtle distinctions in meaning, such as the difference between the propositional attitude verbs 'know' and 'think'. While both are belief verbs, there are differences in their meaning that affect the ways we can use them. 'Know' is a factive presupposition trigger and can only be used to describe true beliefs that we take for granted. In contrast, 'think' is non-factive and can be used to describe beliefs which we do not take for granted and may in fact be false. When do children master this difference? And how do they come to do so? Answers to these questions are central in language acquisition, but also have implications throughout cognitive science given the central role of propositional attitudes and mental state concepts. In this talk, I will present results from a series of studies that integrate behavioral methodologies and corpus analyses to (i) determine when children differentiate 'know' and 'think'; (ii) develop learning theories about the kinds of input cues which might help children differentiate them; and (iii) test whether these cues are actually related to children's comprehension of the difference. Results suggest that children start to master these verbs early within the preschool years, but with variability in age of acquisition. This variability is related to differences in individual children's linguistic input that are indirectly informative about the underlying semantic contrast between the verbs. This allows us to make clear predictions about the kinds of evidence that children use to learn the meanings of attitude verbs and presupposition triggers more broadly. Future work will test these predictions on a wider set of data, including input in different dialects, in different languages, with different presupposition triggers, and within the grammar more broadly.