Polar (yes/no) questions are prototypical cases of Dutch V1-clauses. Although it is normally the V1-order that occurs in written texts, it is possible in speech to mark a polar question by means of a typical rising intonation; cf. Barbiers (2007:103).

Polar V1-questions are normally less marked than polar V2-questions. The primeless examples in (29) are more neutral than the primed examples, which imply a certain expectation on the part of the speaker, or express (lack of) confidence in the truth of the proposition expressed by the clause. In other words, polar V2-questions have a similar function as the tag-questions in the English translations in the primed examples. We will ignore polar V2-clauses in what follows.

      An important question is whether the clause-initial position in polar V1-clauses is truly empty or whether this position is occupied by some phonetically empty polarity operator: [CP OPpolar heeft [TP Peter dat boek gelezen theeft]]? The latter option is argued by Barbiers (2007/2013) on the basis of the left-dislocation examples in (30). The (a)-examples show that in declarative clauses left dislocation is possible with a resumptive pronoun in the middle field or in the clause-initial position. The (b)-examples, on the other hand, show that the resumptive pronoun cannot occur in the clause-initial position in yes/no-questions.

Assessing this argument is hampered by the fact, indicated by the number sign, that examples such as (30b') are acceptable if pronounced with the intonation contour typical of polar V2-clauses such as (28c), which is somewhat easier to get if we add the modal particle toch; Dat boek, dat heeft Peter toch gelezen? This means that we have the two structures in (31): the polar V1-construction in (31a) does not allow movement of the resumptive pronoun in clause-initial position given that this position is already occupied by the phonetically empty polar operator; the polar V2-construction in (31b) does allow movement.

Given that the grammatical and ungrammatical version of (30b') can only be distinguished on the basis of their intonation contour, it would be desirable if we could provide supplementary, independent evidence for the hypothesis that polar V1-structures have a phonetically empty operator in clause-initial position. Such evidence can be provided by the following constructions with the negative polarity phrase ook maar iets'anything'. Example (32a) shows that such phrases cannot occur in positive declarative clauses: as their name expresses, they typically occur in the context of sentential negation, which is expressed in (32b) by the negation on the subject niemand'nobody'.

It is not the case, however, that negative polarity ook maar-phrases are only licensed by a negative operator: example (33a) shows that they may also occur in polar questions. This can readily be explained if we assume that empty polar operators are also able to license ook maar-phrases. The fact that the corresponding polar V2-clause in (33b) does not allow an ook maar-phrase is consistent with Barbiers' claim that such clauses are declarative and thus do not have an empty polar operator. For completeness' sake, note that negation and the polar operator are just two specific cases of a larger set of so-called affective operators that license negative polarity items; we refer the reader to, e.g., Klima (1964), Progovac (1994) and Haegeman (1995:ch.2) for discussion.

The discussion above has provided empirical support for the claim that polar V1-clauses have a phonetically empty polar operator in initial position and are thus only apparent exceptions to the claim that clause-initial positions of main clauses must be filled by some syntactic constituent.