This section concludes the overview of the syntactic classification of adpositions by discussing the structural relationship between the four main classes that have been distinguished. Since this is still relatively uncharted territory, much of what follows is speculative and should be taken only as a first indication of what the structure of adpositional phrases might look like. Some studies dedicated to this issue, like Van Riemsdijk (1978/1990), Koopman (2010) and Den Dikken (2003b), suggest that the correct analysis may in fact be more intricate than suggested here; cf. Broekhuis & Den Dikken (2018) for an illustration.

We begin by discussing the relationship between prepositions and postpositions. One way to describe the difference between the two is to say that prepositions take their nominal complement to the right, while take their complement to the left. Since we have seen that the postpositions are a proper subset of the prepositions, this can be formalized by assuming the lexical entries in (154): (154a) expresses that adpositions that can be used as prepositions only take their complement to the right, whereas adpositions that can be used either as prepositions or as postpositions can take their complement either to the right or to the left.

A problem for the proposal in (154) is that the prepositional and postpositional phrases differ in meaning: the former typically denote a (change of) location, whereas the latter denote a direction. In German, this difference is not expressed by word order but by case marking: both locational and directional adpositions are prepositional, but locational adpositions assign dative case, whereas directional adpositions assign accusative case. Since German and Dutch are so closely related, this casts serious doubt on the lexical entry in (154b). It may be that in Dutch, too, directional adpositions take their complement to the right, but because Dutch has no morphological case, the nominal complement must be moved to the left of the adposition in order to signal directional meaning. This leads to the movement analysis in (155b).

The analysis in (155) might be supported by the fact that the complement of a preposition cannot be scrambled or topicalized, whereas the complement of a postposition can. This would be surprising if they both occupied the complement position of the adposition but would follow naturally if we assume that the base-position of the noun phrase in (155a') is not accessible to these movement operations, whereas the derived position in (155b') is. The relevant data are given in (156).

If the movement analysis of postpositional phrases in (155b') is tenable, a similar analysis may be feasible for circumpositional phrases. Instead of assuming that circumpositions are discontinuous heads, as is done in traditional grammar, one can assume that circumpositional phrases actually consist of an adposition that takes a PP as its complement, which (for some reason) must be moved leftwards; cf. Zwart (1993:365ff.) and Claessen & Zwarts (2010).

The analysis in (157) has several potential advantages. First, it can account for the fact that the PP-part in (157) must have a form that can be used independently as a prepositional phrase. Second, the analysis in (157) leaves open the possibility that not all prepositions can occur as the second member (= the P-part in (157b)) of circumpositional phrases, and that there are certain elements that can occur as the second member of a circumpositional phrase but cannot be used as a preposition. This would follow if we assume that, as in the case of verbs, complementation of adpositions is lexically constrained; adpositions like voor, which can only occur as prepositions, have the categorial frame in (158a), adpositions like heen or vandaan, which can only occur as the second member of a circumposition, have the categorial frame in (158b), and adpositions like aan, which can be used both as a preposition and as the second member of a circumposition, have the categorial frame in (158c).

Third, the movement analysis in (157b) predicts that circumpositional phrases can be split; just like the nominal complement of a postposition, the prepositional complement can be moved further leftwards. This can happen when the prepositional phrase contains a nominal wh-phrase, as in (159), which is taken from Section 32.2.5. Note that this analysis does not shed any new light on the question of why the topicalization of the PP in (157b) generally leads to a marked result.

Finally, the analysis in (157b) can account for the fact that toe occurs both as the second member of circumpositional phrases and as the counterpart of tot in pronominalized PPs like er ... toe in example (160b). It suffices to say that circumpositional phrases and pronominal PPs are both derived by leftward movement of their complements, and that the use of toe (instead of tot) is a morphological reflex of these movements.

A potential problem with the analysis that circumpositions are the result of leftward PP-movement is that movement is often assumed to cause freezing, i.e. the moved phrase becomes an island for extraction; cf. Koster (1978a: §2.6.4.4), Corver (2006b/2017) and Ruys (2008). The data on R-extraction from circumpositional phrases seem to contradict this: the analysis in (157) implies that the PP bij de koffie in (161a) occupies its base position, yet R-extraction is excluded; the PP over het hek in (161b), on the other hand, is said to have moved leftward, yet R-extraction is possible from circumpositional phrases like over het hek heen; cf. Section 32.2.5 for a more detailed discussion of R-extraction.

However, it has been argued that Dutch clauses also have an underlying head-complement order; cf. Zwart (2011: §9) for an excellent review. If this is indeed true, then the preverbal position of a PP-complement is also a derived position, so that also in this case, freezing is also to be expected. However, the examples in (162) show that R-extraction is possible from the preverbal position; it is instead R-extraction from postverbal PPs that is impossible.

This means that on the assumption that Dutch has an underlying head-complement order, the freezing effect cannot be assumed to occur with all types of movement: PP-movement resulting in the PP-V order or the surface order of circumpositional phrases must be assumed not to evoke freezing, but to have the opposite effect of facilitating movement. In any case, the (a) and (b)-patterns in (163) must receive a similar analysis assuming an underlying head-complement order. We leave this for further research.

We conclude with a brief remark on the relation between intransitive adpositions and particles. We have seen that the former probably function as heads of regular adpositional phrases, and that they are special only in that they do not take a complement, or can leave their complement implicit. This is not true of particles. One difference between particles and all other classes of adpositions is that particles are incapable of assigning case; their arguments are typically assigned accusative case by the verb or nominative case in the subject position of the clause, just like the logical subjects of other predicatively used adpositional phrases. There are two analyses that seem to be compatible with this observation. According to the first analysis, particles are just like intransitive adpositions in that they do not take a complement, which then of course begs the question as to why they behave differently from intransitive adpositions. According to the second analysis, particles are like unaccusative verbs in that they do take a complement but cannot assign case to it; therefore, the complement must be moved into a position where it can be assigned nominative or accusative case. Arguments for the second approach can be found in Den Dikken (1995a).