The complex phrase wat voor (een)'what kind of' can be classified together with the wh-word welk(e)'which' as interrogative demonstrative pronouns; cf. Section 5.2.3.1, sub I. Wat voor N phrases differ from welk(e) N phrases in D-linking: whereas the latter instruct the addressee to select certain referents from some referent set previously established in the discourse, the former do not presuppose such a pre-established set and simply instruct the addressee to provide a further characterization of the set denoted by the N in question. In other words, a felicitous answer to a wat voor N question involves a noun phrase denoting a subset of N, whereas a felicitous answer to a welk(e) N question involves a noun phrase referring to one or more discourse entities for which the predicate in the question holds. A prototypical answer to the wat voor question in (225a) is therefore something like (225a'), in which the relevant set of shoes is narrowed down to shoes that are blue and have high heels. This answer would not be appropriate for the question in (225b), since in this case the speaker implies that the relevant set of shoes is already identified; the speaker is specifically asking for the identification of the relevant entity, which is felicitously provided by the answer in (225b').

Out of the blue, (225b') could not be used as an answer to the question in (225a), since it would wrongly presuppose that the person who is asking the question has the necessary background information to determine the referent of the noun phrase. However, if the person who is answering the question provides an additional hint, for instance by pointing to a certain pair of shoes, the answer may become felicitous. The person who answers can also provide additional linguistic clues indicating that the relevant set is or should be known to the speaker: the adverb natuurlijk'of course' in, for instance, die blauwe met hoge hakken natuurlijk may provide such a clue.
      In short, we can say that whereas a welk(e) N question requires as an answer a noun phrase with a unique referent taken from a presupposed set, the wat voor N question merely asks for a further restriction of the set denoted by N (which is not known to the speaker). This distinction also holds if the wat voor phrase is used predicatively. A wat voor N question like (226a) asks for a further specification of the property already ascribed to the subject of the clause (viz. the property of being a book). A welk(e) N question like (226b), on the other hand, asks for unambiguous identification of the book. This accounts for the difference in definiteness of the noun phrases that are given as an answer.