Wh-movement in Main Clause
Generally speaking, wh-movment in main clause means wh-constituent or wh-phrase occupies an initial position of an interrogative root sentence.
This syntactic phenomenon could be explained into two steps.
First, let us have a look at root constituent questions.
a) Thelma will meet Louise after lunch. b) Will Thelma meet Louise after lunch?
a) is a declarative root sentence and b) is an interrogative root sentence. From this case, we could see that in English root constituent questions, two conditions must be met: 1) the interrogative constituent must be in an initial position and 2) the auxiliary must precede the subject. Root interrogatives are characterized by I-to-C movement.
So according to the rules mentioned above, it is obvious that the following two sentences are ungrammatical.
c) *Thelma has met whom? d) *Has Thelma met whom? e) *Whom Thelma has met?
As we have known the rules and main characters of root constituent questions, it will be much understandable when we move to the second step: root wh-question.
f) Whom will Thelma meet after lunch? g) What should he buy?
From the above case, we could see that tow movements take place: 1) the wh-phrase moves to the position in front of C, 2) I-to-C movement occurs, giving rise to subject-auxiliary inversion(SAI). These are the rules for wh-movement in main clause.
We could analyse one sentence by drawing a tree with S-structure.
Whom occupies the clause-initial position, [Spec, CP]. It also realizes the internal argument of meet. When whom moves leftward, it leaves an empty category in its original or base-position, which we indicate by means of t for trace. A trace encodes the previous position of a moved constituent. The auxiliary will starts out under I and moves to C, it also leaves a t.
Please press here to start the next step: Constraints on Wh-movement