A wh-word is one of a fixed inventory of words used for asking questions that are so called because most of them begin with these letters. Examples of wh-words would be who, what, what, which, where and how. A wh-question is a question that involves a wh-word, for example "Who did you see?" can be classified as a wh-question. We can also distinguish wh-phrases, phrases (such as NP or PP) that contain wh-words and is placed at the beginning of a clause. Finally, a wh-question is a question that begins with a wh-phrase.
Wh- questions are interesting in that they appear to violate principles of subcategorization. Basically, subcategorization (usually seen as additional lexical information) tells us whether or not a given word has to come with certain arguments, and if so, it gives us the number and syntactic type of each of these arguments. For instance, the verb 'put' has the subcategorization [ ___ NP PP ], making sentence 1 grammatical but sentences 2 and 3 ungrammatical (since they each lack an argument).
A wh-question such as 4 however is perfectly grammatical!
The underscore is added to show the place where one would expect a PP, but in this case there is really nothing: a gap. You can probably guess that the reason this 'violation' of the subcategorization principle is allowed here is the presence of wh-phrase at the beginning of the sentence. Take sentence 5 as a starting point,
Going from sentence 5 to sentence 4 will involve a ovement of the wh-phrase to the beginning of the sentence. We call this kind of movement wh-movement.
a.) To go from sentence 5 to sentence 4 another kind of movement is needed which is quite typical of making questions in general. Which transformation is that?
b.) Carry out the transformations from sentence 5 to 4 on the following tree and draw the resulting one:
Another way to view wh-movement involves complementizer phrases. Consider the sentence
The verb 'wonder' will usually take some complementizer phrase as argument ('I wonder if...') but here the complementizer is missing. In stead we see an embedded wh-question as argument to the verb. Note that a combination of a complementizer and wh-question leads to ungrammaticiality:
It is possible to view things as if the wh-phrase 'on which shelve' takes the place (fills in the slot) of the complementizer, leaving no more room for 'if' in sentence 7.
c.) Draw a tree for sentence 6 with the C-slot as "landing site" for the wh-phrase. Categorize 'I' as an NP and use C and CP for complementizer and complementizer phrase, respectively. Otherwise use the same categories as in exercise b.
d.) Redraw your tree from exercise b.) here so that it fits into the idea of wh-phrases in the C slot. Hint: as top node you should use CP in stead of S.