 That is, (50) cannot be read as meaning that there is a particular x about which John has some relevant de re attitude of wonder. Part of the problem is that whereas ‘know’ takes both propositional and interrogative complements, ‘wonder’ takes interrogative complements but not propositional complements. This difference between ‘know’ and ‘wonder’ is the distinction between responsive and rogative predicates, which will be discussed in detail in section  4.8,  below.