In this paper I look at light verb, serial verb and auxiliary constructions crosslinguistically and try to set up criteria to distinguish these constructions. I argue that while a coherent set of properties can be found to distinguish light verbs from auxiliaries, it is more difficult to find crosslinguistic criteria which set serial verbs apart from light verbs and auxiliaries. This is because the class of serial verbs is not coherent, i.e. it is not clear which constructions should be considered serial verbs. Nevertheless, when looking at a specific language in detail, it can be established whether a construction may be considered a serial verb.
As a case study, I look at posture verbs in Ngan'gityemerri, a Northern Australian language. In Ngan'gityemerri, posture verbs can be used as simple verbs, in verb + coverb complexes and as clitics which attach to verb + coverb complexes. I show that while these constructions seem to be very similar at first glance, they behave differently when looked at in more detail. Thus, I argue that verb + coverb complexes are complex predicates while the encliticized posture verb should be best analyzed as auxiliary.