Exercise 10.5 CP's do not need case licensing. For that reason, when the verb suspect is passivized, its CP complement can remain in object position, as in (1a). The subject of the passive verb must then be an expletive, because English, unlike many languages, requires that tensed verbs have an overt subject. Because DP's do require case licensing, there must move from the subject position of the infinitive to the subject of the higher sentence when the verb becomes passive.
Evidence that CP's do not need case licensing comes from sentence pairs like:
The puzzling example in the paradigm of examples given in the exercise is (1b), which one might think impossible, since no principle of grammar forces the movement. One possibility, but one with certain problems of its own, is that the verb here is actually an adjective that takes a clausal subject.