In many Oceanic languages in northwest Melanesia the default attribute construction ('a big house') is one whose morphosyntax looks like that of a possession construction: the attribute occupies the (possessed) head slot, the noun the (possessor) modifier slot ('a big one of a house'), that is, the opposite of the cross-linguistic norm and a rare phenomenon worldwide. I briefly describe these constructions, which are morphosyntactically varied, then examine their history, proposing that a major factor in their genesis was the presence in Proto-Oceanic of a small class of adjectival nouns whose reflexes in languages scattered across Oceania either may still behave as noun phrase heads or retain features reflecting this earlier status. The adjectival noun class had a small membership but high token frequency, and provided the template for a pattern extension that in a number of northwest Melanesian languages drew in the much larger adjectival verb class. I also address the question of why this change occurred in northwest Melanesia but not elsewhere in Oceania