Om + te-infinitivals are formally characterized by the presence of the infinitival marker te and the complementizer-like element om. There are at least two analyses available for the infinitival marker te. According to some proposals, te is a bound morpheme prefixed to the infinitival verb, just as ge- is a bound morpheme in past participle forms such as ge-pak-ttaken. This may explain why both te and ge- are usually adjacent to the stem of the verb. An alternative proposal is that te is the T(ense) head of the functional projection TP. See Section 1.3, sub IIIA1, and the references cited there for a more detailed discussion of these proposals.

One reason to assume that the element om is a complementizer and not a preposition is that infinitival complement clauses introduced by this element behave like finite complement clauses and not like PP-complements in that they must be in extraposed position; they obligatorily follow the matrix verb in clause-final position (if present). This can be illustrated by the embedded and perfect-tense counterparts of example (30a) in (31).

Another reason for assuming that om is a complementizer is that it can often be omitted, as in (32a). This would be quite surprising for a preposition, but it is attested for complementizers in many languages: cf. John promised (that) he would send Elisabeth the book. A further reason for assuming that we are not dealing with a PP-complement is that the infinitival clause is not pronominalized by the R-word er in the pronominal PP erom, but by the pronoun dat; this is illustrated in (32b).

It is important to note that the omission of om is not syntactically innocuous; the examples in (33) show that it can make the infinitival clause transparent to extraction of the object of the infinitival clause to a position in the middle field (i.e. to the left of the clause-final main verb) of the matrix clause. The percentage sign in (33b) is added because some speakers object to such examples; cf. Section 4.4.3 for a detailed discussion.

The fact, illustrated in (34a), that this type of extraction is also excluded from finite complement clauses suggests that om + te-infinitivals and finite clauses are of the same categorial type; they are CPs. Infinitival clauses without om, on the other hand, are likely to be less extended verbal projections, which would make TP a likely candidate. The reader is referred to Section 9.1 for an introduction to the functional categories CP and TP.

For completeness’ sake, note that the string Jan heeft het boek beloofd dat hij naar Els zal sturen is acceptable if the postverbal clause is interpreted as a relative clause modifying het boek (“John promised a certain book, namely the book that he will send to Els”), but this is of course irrelevant here.