The suffix -ert still seems productive in deriving nouns from adjectives. Examples are listed below:

These derivations with an adjectival base always denote persons, often with a negative connotation. This implies that the suffix is not added to adjectives with a positive impact, like for instance aardichkind: we do not have a formation *aardichert.

Secondly, -ert can be added to a verb. Here, the suffix may also be productive. Examples are:

The derivations are person names (the first four examples) or instrument names (the two last ones).

It is likely that the suffix -ert came into existence through epithesis/t/ (the so-called paragogic /t/) of derivations with the suffix -er. It is striking that there is a good deal of variation between a form with and without final [t] in most of the forms. An example is flaai(k)ert next to flaai(k)erflatterer. Derivations with Hoekstra (1998: 105)-ert often have a pejorative connotation, while -er is neutral.

There are two examples in which a geographical name can be the base: the inhabitant names > SpanjertSpaniard (from SpanjeSpain) and Bil(t)ker(t)inhabitant of the Bilt area (from BiltBilt, an area in the north of the province of Fryslân). In case of Bil(t)ker(t), both [t]-s are optional, but addition of [k] is obligatory.

Finally, there are derivations with a nominal base, but they do not belong to the daily language anymore. A few examples can be mentioned and in all of them an extra phonological process occurs:

• In tûfe[tufə]crest > tûfert[tufət]a bird with a crest the schwa of the base form has been deleted;
• In moarmer[mṷarmə]marble > moarmert[mṷarmət]marble marble, i.e. a small hard ball of marble used by children to play the game of marbles the second syllable of the base form has been truncated;
• In dau[dɔ.u]dew > daukert[dɔ.ukət]dew worm the segment [k] has been added.

In several derivations we see a segment /k/ preceding the suffix -ert. With nominal bases, its source may be a diminutive form. lytskertbaby; small object, for example, may have been derived from lyts-kesmall-DIMsmall one. Attachment of -ert then results in lytskert. Verbal bases may have provided a base with /k/ after derivation with the suffix -k (for this suffix, see -k deriving verbs from verbs). Thus next to flaaieto flatter there is flaaikjeto flatter continuously, which may have been the source for flaaikertflatterer. Possibly, the variant -kert may have been abstracted from these sources, resulting in an independent variant as in moaikertbeautiful object, sleaukertnegligent person or skierkerthooded crow; old man. Furthermore, parallellism with the allomorphy that exists in diminutives may have led to the allomorph -tsjert. We see this form in the birdnames gieltsjertyellow-hammer and grautsjertcorn-bunting. It is striking that many derivations are attached to a base ending in a vowel. The segment /k/ could have the function of a hiatus filler here.