Suppletion is local: Evidence from Hiaki. In The structure of words at the interfaces

Bobaljik (2012) proposes that the insertion of suppletive vocabulary items can be sensitive to features within the same maximal projection, but not across a maximal projection boundary. Among heads (X0 nodes), this condition restricts suppletion to synthetic formations and excludes suppletion in analogous analytic formations. In Hiaki, however, the number of a subject DP can trigger verbal suppletion in certain intransitive verbs. The verbs in question, however, can be shown by language-internal diagnostics to be unaccusative. Suppletion, then, is in fact triggered by an element within the maximal projection of the suppleting verb. The analysis supports the position that internal arguments are base-generated as sisters to their selecting verb (Kratzer 1996; Marantz 1997; Harley 2014). Further, we see that the locality condition does not distinguish between word-internal and word-external triggers of suppletion, but is rather a condition of structural locality, showing that morphological structure is, in a fundamental way, syntactic.