Rachel Dudley · The role of input in discovering presupposition triggers: Figuring out what everybody already knew
This dissertation examines how children discover the subtle contrast in meaning between know and think. Unlike think, know is both veridical and factive, so uses of it entail and presuppose the truth of the proposition expressed in the complement clause. Thus, speakers should only be able to use (1) when they know that (3) is true and can be taken for granted, while uses of (2) can also occur in situations where (3) is taken to be false.
(1) John knows that Mary is home.
(2) John thinks that Mary is home.
(3) Mary is home.
The dissertation asks how children uncover such restrictions on the use of know, as compared to think, by bringing together behavioral methods and corpus methods. Behavioral studies indicate that children begin to understand the factivity of know around 3-5 years of age, with much individual variation in when this discovery occurs. Corpus analyses suggest that children between 3-5 are not provided enough direct evidence about the contrast in (1-2), partly because they rarely hear sentences like (1) and partly because they may not realize that propositions like the one expressed in (3) are taken for granted when (1) is uttered. Instead, children most likely learn about the contrast in (1-2) through more indirect evidence, such as contrasts in the syntactic (4-5) and pragmatic (6-7) distributions of the verbs.
(4) John knows where Mary is.
(5) * John thinks where Mary is.
(6) Do you know what time it is? (intending: What time is it?)
(7) I think it's 3pm. (intending: It's 3pm.)
These data also help to illuminate the acquisition of similar expressions, such as attitude verbs and presupposition triggers, whereby the everyday use of such words initially obscures their underlying meanings and syntactic and pragmatic bootstrapping mechanisms help to illuminate them.