In Frisian complementizers end in /t/, which is either an integral part of the complementizer or it is the 'conjunction morpheme' t /t/ − written 't −, with which relative and interrogative pronouns and temporal and local adverbs are inflected in case they function as a complementizer. Some complementizers show up without /t/ when combining with the clitic allomorph of some personal pronouns. Overviews of the relevant complementizers and clitics are given in (1) and (2), respectively (see also Visser (1988:206-212)):

The modal verb moatte /matə/ must − to be precise, its stem moat /mat/ − joins this pattern. Examples are given in (3). Note that not all sequences in bold are recognized in the official spelling.

Of the clitics in (2), 'k is the only one without a vowel. This implies that 'k does not add a syllable to the host word it joins, so that sequences like dat 'k en moat 'k end up as monosyllabic. There are limits to the consonant sequences a syllable may accommodate. For reasons of sonority profile, the final sequence /-tk/ of dat 'k /dɔtk/ and moat 'k /matk/ cannot survive. It seems 'logical' that the final /t/ of dat and moat gives in, in favour of /k/, since otherwise the clitic 'k would be lost altogether. This is why the full forms dat and moat can only combine with ik's reduced variant ek /ək/. In that case, however, the /t/-less variants of dat and moat are out, for their amalgamation with vowel-initial ek would create the ill-formed configuration of two word-internal vowels in hiatus (see The resolution of vocalic hiatus): da ek /*dɔək/ and ma ek /*maək/, respectively. Since we, je, and jem are not vowel-initial, they can freely combine with the /t/-less variants, as exemplified in (3).

The forms in (2) above − 'k /k/ I, we /və/ we, je /jə/ you (SG, polite), and jem /jəm/ you (pl., familiar and polite)− all happen to be the clitic allomorphs of the subject form of personal pronouns. That this is not coincidental, is shown by je and jem. These are a) personal pronouns with identical forms for the subject and the object form and b) personal pronouns the forms of which equal those of the related possessive pronouns. Now see the examples in (4):

There appears to be an asymmetry here between the subject form on the one hand and the object form/possessive pronoun on the other. As yet, there does not seem to be a ready explanation for the above pattern.

The relation between the full form of the complementizers and their /t/-less variant in host word + clitic combinations might be expressed as follows:

A similar statement must be made with respect to the verb moat: