Some languages treat unergative verbs differently from other intransitives in morphosyntactic terms. For example, in some Romance languages, such verbs use different auxiliaries when in compound tenses.
Besides the above, unergative verbs differ from unaccusative verbs in that in some languages, they can occasionally use the passive voice.
In Dutch, for example, unergatives take hebben (to have) in the perfect tenses:
- Ik telefoneer – ik heb getelefoneerd.
- "I call (by phone). – I have called."
- Er wordt door Jan getelefoneerd.
- "*There is by Jan telephoned." (literally "A telephone call by Jan is going on.")
By contrast, Dutch ergative verbs take zijn ("to be") in the perfect tenses:
- Het vet stolt – het vet is gestold
- "The grease solidifies – The grease has solidified."
In that case, no passive construction with worden is possible. In other words, unergatives are truly intransitive, but ergatives are not.