3.2.4 Locality Restrictions on movement
This movement is known as raising as the subject of the lower clause raises to the subject of a higher clause.
18.104.22.168 Unaccusatives and ergatives
This is a case of raising, as introduced in chapter 3. In (62a) the subject of the lower clause is raised into the subject position of the raising verb seem, demonstrating that this position must have been empty at D-structure. In (62b), however, the thematic subject of the lower clause does not move out of this clause. In this case the subject position is filled by another expletive element it. It would be ungrammatical for this position to be left empty, an indication that all English sentences must have subjects regardless of whether one is semantically demanded or not. We will return to this observation in the next chapter. Note however that this expletive subject differs from the one used in there constructions, though their function (to fill a vacant subject position) seems to be similar. It would be ungrammatical to use a there in raising structures and it in there constructions:
In this chapter we have dealt with a number of phenomena concerning non-finite clauses in English. On the whole, the interesting aspect of these constructions concerns their subjects. We have seen various possibilities for empty subjects in non-finite clauses, as with raising and control structures, and also exceptional accusative subjects in other constructions as with exceptional and small clauses. The gerund offers problems for analysis all of its own. By and large, we have offered analyses for all these structures, but have left many issues undiscussed and have ignored many alternative analyses. We might hope that this book has interested the reader sufficiently for them to follow up what has been left out here in further reading and research.