Verbs of body posture may function as aspectual auxiliaries when they combine with to-infinitives. Clause-union is obligatory, as is clear from the cases in the example below:

If the copula of body posture takes a locative complement, however, it is possible to provide it with an optional full infinitival clause. An example is given below:

The infinitival clause presumably functions as an adjunct in case there is a locative complement. No extraction is allowed from the infinitival clause:

Extraction is licit if there is clause-union and the infinitival verb is clustered with the body posture copula, so that the arguments of the infinitival verb are realised to the left of the copula of body posture, as in the sentence below:

clause-union and verb-clustering always appear together with auxiliaries of body posture. So auxiliaries of body posture do not allow of the third construction, in which arguments of the main verb may appear both to the right and to the left of the copula. The following sentence illustrates that verbs of body posture resist the third construction, regardless of whether a locative phrase is present:

Such sentences are allowed with verbs selecting the third construction:

The grammaticality of such examples indicates that the presence of the third construction is independent of the presence of the IPP effect, seeing that the IPP-effect is absent in Frisian. Furthermore, examples of the third construction can even be found in the nineteenth-century (in the work of the writer Waling Dykstra, for example). If the third construction in Frisian is an interference from Dutch, it is an old one.

To sum up, auxiliaries of body posture may take a locative complement and a full infinitival adjunct clause, or the infinitival clause functions as the complement, but in that case clause-union and verb clustering must take place. If verb raising takes place, the copula of body posture is invariably adjacent to the main verb, which has the form of a to-infinitive. This observation holds true in clauses in which no verb-second has taken place, since verb-second obscures the visibility of this generalisation, that is, verb-second breaks up the adjacency of the two verbs by moving the tensed verb to the beginning of the clause.

There is one exception, though, concerning the adjacency of the aspectual copula and the to-infinitive. Verbal particles may intervene between the aspectual copula and the to-infinitive, as shown below, in case the to-infinitive follows the copula, which is the unmarked word order:

However, the to-infinitive occasionally is found to precede the aspectual copula, as in the example below:

If the verb cluster has a head-final order, as in the example above, it is impenetrable to non-verbal material such as particles, as illustrated by the minimal pair below:

Aspectual auxiliaries of body posture are rarely used in the perfect tense, the examples from the Frisian Language Corpus (FLC) tend to be recent and, moreover, they have been produced by only a few writers. The FLC contains a lot of Frisian from before the eighties, so that it may well be telling that the examples encountered are quite recent:

The fact that such examples are of a recent date suggests that this use of aspectual auxiliaries is due to interference from Dutch, although the examples do not have the feel of interference, that is, they seem to be well entrenched in Frisian.

The to-infinitive accompanying the verb of body posture is commonly a verb of activity which is compatible with the meaning of the verb of body posture. A person can talk while standing, or slumber while lying, and so on. The to-infinitive following the aspectual verb of body posture must exhibit incorporation of the direct object if the subject is inanimate:

It should be noted that it does not seem grammatical to realise the direct object as a syntactic Noun Phrase (NP) in (12), as shown below:

Most examples in the FLC involve intransitive to-infinitives. Transitive to-infinitives are rarely found as the complement of body posture auxiliaries, they have a decidedly Dutch feel and they are all recent. It seems that they must involve animate subjects. Some examples are given below:

In these examples, it sounds better to leave out the aspectual copula all together and turn the infinitival verb into the tensed verb, as in the example below:

Transitivity can also be avoided by incorporating the direct object, resulting in a perfectly sounding sentence, as in the following examples:

Incidentally, particles can also be incorporated, as in the following example:

To sum up, auxiliaries of body posture select intransitive verbs of activity, in case they select infinitival clauses as their complement. It seems to be a recent development that auxiliaries of body posture are found with transitive complements, that is, without incorporation. The relevance of intransitivity is intimately bound up with object incorporation, since object incorporation makes a transitive verb intransitive. More specifically, the kind of intransitivity involved is not the removal of the logical subject (the agent) from the subject position, but it involves the removal of the logical object (the theme) from the object position. This process, when marked by a systematic morpheme, is called a syntactic antipassive. The Frisian examples involve an antipassive that is realised by noun incorporation. Consequently, it could be said that various Frisian copulas and auxiliaries select an antipassive complement, and that antipassivity is lexically realised by means of noun-incorporation, see incorporating to-infinitive.