Some adjuncts appear to be extraction islands, as shown in d79, while unbounded dependencies into complements are generally possible, as shown in d80. This provides a further syntactic test for the adjunct/complement distinction.
*Which endangered species did Sandy meet someone
fond of ? [P&S 1987, (260c)]
Which endangered species did Kim impress you as being most
fond of ?
[P&S 1987, (261c)]
The data in d28-d34 therefore suggest that the dative prepositional phrases are complements rather than adjuncts, since the objects of the PPs can be extracted.
Whom did Adam give a book to ? Whom did Adam kick a ball to ? Whom did Adam bake the cake for ?
Pollard and Sag acknowledge, however, that certain adjunct types do appear to sanction internal gaps, as shown in d32-d33. One would not want to assume that sleep and die subcategorise for without-PPs, as these PPs do not seem to contribute an argument which plays a role in the main verbal relation.
This is the blanket that Rebecca refuses to sleep without . [P&S 1987, (264a)] Which symphony did Schubert die without finishing ? [P&S 1987, (264c)]
Furthermore, one of the examples they give of an ungrammatical sentence with an adjunct-internal gap, shown in (3.43a), seems to become more acceptable with a different adjunct, as in (3.43b). The change involves replacing the ``motivational'' adjunct with a -PP (which again one would not want to assume without question is a subcategorised complement), suggesting that this type of PP allows internal gaps.
*Which famous professor did Kim climb K-2 without oxygen in order to impress ? [P&S 1987, (260b)] Which famous professor did Kim climb K-2 without oxygen for ?
Due to the problems with this test, it is very likely incorrect to assume that the data in d28-d34 necessarily indicate that the dative PPs should be treated as complements.