Chapter 5 and Chapter 6 have discussed cases in which, respectively, a main and a non-main verb take a clause or a smaller verbal projection as their complement. We have seen that finite clauses introduced by the finite complementizer dat'that' or of'whether' and infinitival complement clauses introduced by the complementizer-like element om are normally in extraposed position, that is, placed after the matrix verb in clause-final position. This is illustrated in the examples in (3), in which the matrix verb is underlined and the complement clause is in square brackets with the categorial label CP (= complementizer phrase). Since CPs do not allow splitting, we can put such cases aside for our present purpose.

Infinitival clauses without the complementizer-like element om are sometimes also in extraposed position, but sometimes also allow or even require clause splitting, which is what we typically find if the complement clause is a bare infinitival clause. This is illustrated in the examples in (4) in which the dependent bare infinitival is in italics; in (4a) the matrix verb is a main verb, whereas in (4b) it is the aspectual non-main verb gaan'to go'. We underlined the verbs in order to push to the fore that clause splitting results in clustering of the verbs in clause-final position.

The examples in (5) show that in the northern varieties of Dutch, verb clusters are normally impermeable. This is clear from the fact that the objects of the bare infinitives cannot follow the clause-final matrix verbs; see Section 7.4 for a discussion of a number of exceptional cases. The percentage signs indicate, however, that permeation of the cluster is possible in some southern varieties of Dutch, especially in West-Flanders; cf. Sections 5.2.3 and 6.2, and Barbiers (2008:ch.2). For ease of exposition, we will follow the northern intuitions in the discussions below and simply mark permeated verb clusters as unacceptable.

Constructions such as (4) are not only special in requiring verb clustering, but also because they exhibit a special behavior in the perfect tense; while verbs governed by a perfect auxiliary normally appear as past participles, the non-finite verbs in (4) appear as infinitives if governed by a perfect auxiliary. This so-called infinitivus-pro-participio (IPP) effect is illustrated in (6).

Section 5.2.2.3 argues that verb clustering and the IPP-effect go hand in hand, and can in fact be used as diagnostic properties of structures exhibiting monoclausal behavior, that is, structures consisting of two separate clauses but behave as if we are dealing with one single clause; see Table 1.

	monoclausal	biclausal
verb clustering	+	—
infinitivus-pro-participio	+	—

If so, the notions of clause splitting and verb clustering do not have the same extension: the extension of the latter is a subset of the extension of the former. That clause splitting need not involve verb clustering in the technical sense of the word can be shown by the examples in (7). Example (7a) first shows that te-infinitival complement clauses may also be split by the finite verb in clause-final position. This example differs from those in (4), however, in that the object of the infinitive may also follow the matrix verb in clause-final position, as is shown by (7b). Example (7a) also differs from those in (4) in that it does not exhibit the IPP-effect; in the perfect-tense example in (7c) the verb beweren'to claim' surfaces in its participial form and cannot surface as an infinitive.

If verb clustering and the IPP-effect do go hand in hand, we have to conclude that (7a) does not involve verb clustering. Section 5.2.2.3 therefore analyzed (7a) as a case of remnant extraposition, that is, the infinitival clause is in extraposed position but its object is extracted from it by leftward movement across the finite verb; see Section 4.4.3, sub IV, for a more extensive introduction to this notion. The structure of this example is therefore as indicated in (8); see Reuland (1981), Den Besten & Rutten (1989), Rutten (1991), Broekhuis et al. (1995), and many others.

Support for the analysis in (8) comes from the fact that if the embedded te-infinitive has two (or more) dependents, they may occur on different sides of the matrix verb beweren, although this option is generally considered marked, as compared to the two alternative orders.

Example (9b) can neither be derived by extraposition of the full te-infinitival nor by verb clustering, but it can be derived by what we have called remnant extraposition, that is, extraposition plus leftward movement of the indirect object Marie. If this analysis is viable, example (9c) can, of course, be analyzed in a similar way as (9b) by leftward movement of both the indirect and the direct object. The examples in (9) can thus be analyzed as in (10).

      Section 5.2.2.3 has also shown that some cases of splitting of te-infinitivals do involve verb clustering in the technical sense. Consider the primeless examples in (11), which at first sight suggest that proberen is just like beweren.

However, when we consider the perfect-tense counterparts of these two examples in (12), we see that they exhibit different behavior with respect to the IPP-effect: whereas the verb proberen can appear either as a participle or as an infinitive in the split pattern, it must appear as a participle in the non-split pattern.

If verb clustering and the IPP-effect are two sides of the same coin, we should conclude that (11a) is actually ambiguous: it involves remnant extraposition if proberen surfaces as a participle in the corresponding perfect-tense construction in (12a), but verb clustering if it surfaces as an infinitive. This conclusion receives more support from a consideration of cases in which the infinitive has two or more dependents. The primeless examples in (13) show that the IPP-effect can only occur if all dependents precede the finite verb in clause-final position.

The examples in (14) show that all examples in (13) become acceptable if we replace the infinitive proberen by the participle geprobeerd, but then we are no longer dealing with verb clustering but with (remnant) extraposition. As in (9), placing the dependents of the infinitive on different sides of the matrix verb (here: proberen) is generally considered marked, as compared to the alternative orders.

      The discussion above has revealed that there are two tests which we can apply in order to determine whether we are dealing with verb clustering or (remnant) extraposition: (i) only the former exhibits the IPP-effect, and (ii) only the latter allows permeation of the verbal sequence by the dependents of the embedded main verb (in the northern varieties of Dutch). Our discussion in Sections 7.2 and 7.3 will only consider cases that satisfy both tests.