The verb_cluster constraint ensures that cross-serial word order is obligatory for verbs subject to cross_serial. To rule out the ungrammatical (7a), for instance, we assume that Bea kussen is not a verb cluster. The verb kussen by itself, however, is unspecified for VC, and thus (6a) is not excluded.
We do not assume that cross-serial verbs take lexical arguments (as has sometimes been suggested), as that would rule out the possibility of complex constituents to the right of cross-serial verbs altogether. If one assumes that a possible bracketing of the verb cluster in (6b) is [wil [zien kussen]] (coordination and fronting data have been used as arguments that this is indeed the case), a cross-serial verb must be able to combine with non-lexical verb clusters. Furthermore, if a verb selects a particle, the particle can optionally be included in the verb cluster, and thus can appear either to the right or to the left of a governing cross-serial verb. For a verb cluster containing two cross-serial verbs, for instance, we have the following possibilities:
A final piece of evidence for the the fact that cross-serial verbs may take complex phrases as argument stems from the observation that certain adjectival and prepositional arguments can also appear as part of the verb cluster:
Cross-serial verbs select a +VC argument. Therefore, all phrases that are not verb clusters must be marked -VC. In general, in combining a (verbal) functor with its argument, it is the argument that determines whether the resulting phrase is -VC. For instance, NP-arguments always give rise to -VC phrases, whereas particles and verbal arguments do not give rise to -VC phrases. This suggests that NP's must be marked -VC, that particles and verbs can remain unspecified for this feature, and that in the syntactic rule for application the value of the feature VC must be reentrant between argument and resultant.