'Action-verbs [...]: The relation of these (vocalic) patterns to verbal meaning are not rigid, and a shift from one vowel class to another is not infrequent; nonetheless the following general tendancies are observable, the a/u and a classes contain transitive verbs: the u class intransitive: the i class transitive whose result is produced by a momentary action, and some intransitive verbs of motion. State-verbs are predominantly of the i-type, but the stem vowel a is also found...'
- Ségéral (2004), a pag.299