The examples in (90) demonstrate that R-extraction is possible if the adpositional phrase acts as a PP-complement or as a complementive. That R-extraction is possible from the PP-complement of the verb wachtento wait, can be seen from the fact that in (90a) the adverbial phrase de hele dagthe whole day intervenes between the R-pronoun and the preposition op. Similarly, that R-extraction is possible from PPs acting as complementives can be seen from the fact that in (90a) the accusative object het boekthe book intervenes between the R-pronoun and the preposition in.

On the other hand, adverbially used adpositional phrases generally do not allow R-extraction, as shown in (91); the (b)-examples show that, despite the fact that R-pronominalization of the temporal voor-PP is fully acceptable, R-extraction leads to an unacceptable result.

The examples in (90) and (91) suggest that R-extraction is only possible with PP-complements and complementives. This would be consistent with a generalization from the generative literature (formulated as part of Huangʼs (1982) condition on extraction domains), according to which adjuncts are islands for extraction. However, there a group of adpositional phrases (traditionally analyzed as adverbial clauses), which do allow R-extraction. This group is characterized by the fact that they introduce a participant with a specific semantic role (agent, causer, goal, possessor, etc.); cf. Section 36.2.1, sub IIIA, for discussion. R-pronominalization in this group is illustrated in (92) for a van-PP expressing a source/cause in the (a)-examples and for an instrumental met-PP in the (b)-examples.

Two possible conclusions now present themselves: either we assume that the generalization that only PP-complements and complementives can undergo R-extraction is incorrect, and that R-extraction can also apply to the subset of adjuncts discussed in Section 36.2.1, sub IIIA. Alternatively, we pursue the unconventional assumption that these adjuncts also function as a kind of complement of the verb, even though they differ from PP-arguments and complementives of the kind in (90) in that they are not obligatory. In the absence of clear evidence in favor of either alternative, we must leave the question of which alternative is correct open, noting that both approaches are fraught with problems.

In addition to the requirement that the adpositional phrase must be a complement, a complementive, or an PP that introduces a participant with a specific semantic role, it should also occupy a specific position in the clause in order to license R-extraction: the stranded preposition must be left-adjacent to the verb(s) in clause-final position (with some qualifications that will come up later). This is illustrated in (93) by the pronominalized form of the instrumental PP met een breekijzer from (92b); R-extraction from the pronominalized PP daarmee is possible if it is left-adjacent to the clause-final verbs but not if it precedes the negative adverb niet or if it is placed in a position following the clause-final verbs.