Phasehood of DPs. A study of Japanese noun-verb incorporation

Noun-Verb Incorporation (NVI) is optional with some nominals but obligatory with others in Japanese. In this paper, I argue that the obligatory or optional nature of NVI comes from a structural difference between nominals. I claim that one type of nominal can be realized either as a DP or an nP, and that the other type of nominal can only be realized as an nP, assuming that the structural realization is closely tied to the argument structure of the nominals. Based on this, I provide an explanation where an nP option yields an incorporated form via the operation MOVE, while a DP option provides an unincorporated form via the operation AGREE.