“…The choice of the perfective auxiliary is also thought to involve a privileged syntactic relation between the subject and the object position and therefore to correlate with other syntactic properties of unaccusativity/unergativity, although, as pointed out by Grimshaw (1990; see also Alexiadou, Anagnostopoulou & Everaert, in press), the structural distinction underlying the choice of auxiliaries is less transparent than for other diagnostics. 2 Impersonal passivization is due to the absorption of the subject theta-role and thus requires the presence of an external argument (Grewendorf 1989, Hoekstra & Mulder 1990; it is therefore regarded as a test for unergativity, since the single argument of unaccusative verbs is, by definition, internal.…”