Tongan has an ergative case system, in which the subject of intransitive verb (S) bears the same case (ABS) as the object of a transitive verb (O), while the subject of a transitive verb (A) bears a special case (ERG). Ergativity in Tongan is manifested also at the level of syntax. Tongan consistently treats S and O as equivalents in syntactic operations such as relativisation and coordination. In §5.1, it will be shown that S and O undergo ordinary relativisation, while A requires a resumptive

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... pronoun in the position vacated by the movement. In §5.2, we will consider three coordinate constructions. First, pea coordination disallows S/O to be coreferential with A both as an antecedent and as a gap, suggesting that pea connects arguments in the same structural case position. Second, 'o-coordination allows only S/O to be an antecedent. We propose that the latter arises because the gap in 'o-coordination is a null anaphor, which must be bound by the closest potential antecedent, i.e., NP in the lower position of the matrix clause, perhaps reflecting Rizzi's (1990) relativised minimality condition. There is also mo-coordination, which shows an accusative rather than ergative pattern. We propose that obligatory theta-role identification applies to the arguments in [Spec, VP] at the base structure, thus requiring the two verbs connected by mo to have the same subject. Thus, the accusative pattern reflects not the case but the theta-role (i.e., grammatical function) of the arguments. Altogether our data show that the structural position [Spec, Agro], which we assume is the position where ABS