Unaccusative verbs and Unergative verbs: Weird language stuff

 In linguistics, an unaccusative verb is an intransitive verb whose grammatical subject is not a semantic agent. In other words, the subject does not actively initiate, or is not actively responsible for, the action expressed by the verb. An unaccusative verb's subject is semantically similar to the direct object of a transitive verb or to the subject of a verb in the passive voice. Examples in English are "the tree fell"; "the window broke". In those sentences, the action (falling, breaking) can be considered as something that happened to the subject, rather than being initiated by it.

Now studies of language acquisition have shown that children learning their first language have no trouble distinguishing between unaccusative verbs and their opposite, unergative verbs, such as run or resign, which describe actions voluntarily initiated by the subject. But the second language presents difficulty in the same kind of semantic recognition.