The now standard analysis within HPSG of such verb-clusters is based on ideas from Categorial Grammar (cf. for example ) and defined within the HPSG framework by . In this analysis auxiliary verbs subcategorize for an unsaturated verb-phrase and for the complements that are not yet realized by this verb-phrase. In other words, the arguments of the embedded verb-phrase are inherited by the auxiliary.
For example, the auxiliary `wil' might be defined as in figure 1.
If we assume an application rule that produces flat vp-structures, then we obtain the derivation in figure 2 for the infinite verb-phrase