Postpositions in Japanese play functionally important roles and yet are difficult learn for Japanese as a Foreign Language (JFL) learners. It has been pointed out that the locative particles 'ni' and 'de' are difficult to acquire even for advanced learners (Matsuda & Saito 1992, Kubota 1994, Sakoda 1999). The present cross-sectional study reports on developmental changes in the use of these postpositions by JFL learners, primarily as shown in oral interviews (approximately 6 hr in total).
30 English native speakers of Japanese participated in this study. Based upon the SPOT scores, they were classified into three proficiency levels (beginning, intermediate, and advanced.) The participants completed the following tasks: 1) Japanese interview, 2) English survey on their strategies in using the locative postpositions, 3) Japanese decontexualized cloze test. Overall Japanese interview results were the following: 1) the order of acquisition is: Goal marker 'ni'> Stative Location 'ni' > Place for Action Verbs 'de'; 2) overuse of 'ni' occurred at the beginner stage, while overuse of 'de' occurred at the Intermediate stages, 3) postposition dropping was frequently observed at the beginner and intermediate stages, 4) the nature of postposition dropping by advanced learners is the same as that by native speakers, 5) the most frequently occurring error is confusion between 'ni' and 'de'. The English survey supports Iwasaki (2001) who argues that the "one-to-one" principle of Andersen (1984) plays an important role in the learning of the Japanese locative postpositions at different stages. The decontexualized cloze results confirm Sakota (1999), who claims that JFL learners postulate a hypothesis by paying attention to the semantic cues of locative nouns which precede the locative postpositions (cf. Masuda 2001). This paper concludes with a discussion of pedagogical implications of the data.