Following Kuroda (1965), Miyagawa (1989) classifies post-NP particles in Japanese into two categories, post positions and case markers.Post positions such as kara‘from’and de ‘with’ project their own maximal projections, where as case markers suchas the nominative ga and the accusative? directly cliticize onto an NP, without projecting a maximal projection. Particle ni presents as erious challenge to this analysis because it shows characteristics of both case markers and postpositions (as well as some other categories).In this paper, we examine the behavior of ni in various contexts and show that the reare four types of ni: The dative case marker, the post position ni, the ni of ni insertion, and a form of the copula. The last two categories being irrelevant to Kuroda's dichotomy, ni infact neatly fits into Miyagawas analysis of this dichotomy. Thus, the problem is only apparent. We also discuss issues concerning acquisition of ni. It is suggested that the dative case marker ni and the post position ni can be discriminated by the “affected ness” of the reference of the NP they attach to.