5.2.8 Verbs with clausal complements

The data demonstrate that certain things which are possible when there is a DP subject, are not possible with a clausal ‘subject’. For instance, the auxiliary can move to the front of the clause to form a question in (151a), but not in (151b) where there is a clausal subject. In (152a) we can see that an object can be moved to the front of the clause in what are called topicalisation structures, but not when the subject is clausal (152b). These observations might suggest that the clausal subjects are in a position which prevents the relevant movements and that DP subjects sit in a different position which does not interfere with them. Obviously the DP subjects sit in Case positions, as required by the Case filter and therefore our conclusion is that clausal subjects do not sit in the Case position that the DP subject sits in. All this might be accounted for if we assume that clauses avoid Case positions and this would warrant the clause moving out of its D-structure position in (147) into a position that is Caseless. We therefore assume the following principle: