The distinction between unergative and unaccusative verbs is very relevant to the continental West Germanic languages, including the Frisian ones. They all use the verb to have to construct the perfect tense of unergative verbs, and they all use the verb to be to conjugate the perfect tense of unaccusative verbs. This can be illustrated by presenting the perfect tense of the two sentences above:

The unergative verb fuddelje ‘stagger, botch up’ is conjugated with to have in the perfect tense, whereas the unergative verb strumpelje ‘stumble, trip’ is conjugated with to be, like a passive verb.

Now, it must also be noted that unergativity and unaccusativity are not always inherent lexical properties of verbs. There are verbs that can be used as activity verbs or as theme oriented verbs. Put differently, some verbs can be used either as unergatives or as unaccusatives. For example, the literal meaning of fuddelje is to stagger. In the following example it is used as an acitivity verb:

Correspondingly, it forms the perfect tense with to have. But it can also be used as a verb which focuses not on the activity but on a change of location. The latter use is characteristically unaccusative, as in the following example:

Gunge ‘to go’ and kume ‘to come’ are prototypically unaccusative verbs, but also verbs in which the argument is viewed as a theme rather than as an active participant. However, if an unaccusative verb is combined with the reflexive pronoun, it tends to behave as an unergative. Hence we find pairs like the following:

It seems that some non-reflexive unaccusative verbs alternate with reflexive counterparts which are unergative. As we know that the reflexive marker is a borrowing from Low German, the same could be true for the reflexive use of the verb. Thus not just the reflexive marker was borrowed, but also specific argument frames, involving a change in the selection of the auxiliary of the perfect. We are just scratching the surface of this phenomenon, which merits further investigation.

Past participles of unaccusative verbs have the further property, like passive participles, that they can be used in the attributive construction to modify a following noun, whereas past participles of unergative verbs cannot be thus used.

The aspectual verb weze ‘to be’ may itself be conjugated in the perfect tense either with weze ‘to be’ or with häbe ‘have’. The choice of auxiliary of the perfect is sensitive to the meaning and constructional use that is made of the verb. In the majority of cases, the perfect tense of weze ‘to be’ is constructed with to be. There is, however, a sprinkling of examples in which the perfect tense is constructed with to have. Consider first the example given below:

In this example, the auxiliary of the perfect is not tensed but infinitival. It seems that to have is relatively more often used as the auxiliary of the perfect to weze if the auxiliary of the perfect has the form of the infinitive. This is also the case in West Frisian. It should also be noted that this example involves a logical deduction or probability. This is a characteristic environment for using infinitival häbe ‘have’ as the auxiliary of the perfect for wezen ‘been’, as it further evidenced by the following examples:

In fact, all three infinitival examples feature to have rather than to be as the auxiliary of the perfect. Furthermore, a search for wezen weze ‘been be’ yielded no hits in Fort’s dictionary. See on this Hoekstra & Wolf (2004). They argue that this sequence is generally avoided because the similarity of the two words is too big, and natural language tends to avoids sequences of two adjacent words which are highly similar in form and meaning.

However, it is conversely not the case that tensed forms of häbe ‘to have’ are completely excluded from functioning as auxiliary of the perfect to wezen ‘been’. This is illustrated by the following example:

The use of to have as the auxiliary of the perfect here is probably motivated by the fact that the meaning of the verb and the role of the subject is perceived as being quite active, that is, as involving volition and agentivity.

Modal verbs are conjugated in the perfect tense with the auxiliary häbe ‘to have’. Some examples are given below:

It can be appreciated that the verb clusters are head final: the main verb comes first in the verb cluster, followed by its selecting (governing) verb, and so on.

The past tense of häbe ‘to have’ and weze ‘to be’ can be used as a counterfactual, in examples like the following:

The verb is not marked for counterfactuality or subjunctivity. It just has the form of the simple past. Incidentally, the last sentence is also an illustration of a construction which is termed in Dutch balansschikking ‘balanced coordination’: it involves two main clauses of which the second sketches a hypothetical consequence which is correlated with a very small hypothetical degree difference (compared to the actual degree) expressed in the first main clause. In Dutch and West Frisian, the second main clause is introduced by the disjunctive complementiser rather than by the conjunctive complementiser. This is occasionally found in West Frisian as well.

Verbs with two Noun Phrase (NP) arguments may either be unaccusative or unergative, that is, they may be conjugated in the perfect tense either with häbe ‘to have’ (unergative) or with weze ‘to be’ (unaccusative). Unaccusative verbs tend to have an argument frame in which the theme argument is realised as the subject, and the experiencer as the indirect object. This holds especially true of the verb fale ‘fall’. It may even combine with an adposition to describe a mental state:

However, Saterland Frisian fale ‘to fall’ is much less productive than its West Frisian or Dutch equivalent in combining with adpositions to describe mental states. Mental states can also be described with reflexive unergative verbs, as in the following example:

Unergative verbs tend to express the theme within VP, either as the direct object or as a PP. Thus the theme subject is expressed as the subject with unaccusative verbs, and as an object with unergative verbs. There are small differences between West Germanic language with respect to the question whether a given verb is unaccusative or unergative. For example, German beginnen is conjugated with to have, whereas Dutch beginnen is conjugated with to be. It would be interesting to conduct a systematic investigation of Saterland Frisian with respect to this phenomenon.