The intuition that the class of intransitive verbs is not homogeneous has received substantial independent support under the rubric of the Unaccusative Hypothesis [...]. Perlmutter notes that not all intransitive verbs show the same syntactic behaviour. The subject of some intransitives, the "unergative" verbs, pattern like the subjects of transitives with respect to a large number of syntactic phenomena, while the subjects of others, the "unaccusative" verbs, pattern like the objects of transitives.
- Levin (2004), a pag.313