This paper aims to present the results of a learner corpus study on spoken and written narratives by Japanese learners of English using Processability Theory (PT) (Pienemann, 1998). PT assumes that there is a universal hierarchy of second language (L2) development and many studies (e.g., Di Biase, Kawaguchi, & Yamaguchi, 2015; Pienemann, 1998) have shown support for PT stages for English L2. However, few PT studies have addressed the issues of whether learners use linguistic structures in the same way in spoken and written tasks. The current study focuses on learners’ use of plural marking on nouns, since contradictory results have been reported for the developmental sequence of lexical plural -s and phrasal plural -s (Charters, Dao, & Jansen, 2011). The participants in this study comprised 291 university students learning in English programs in Japanese universities. Each of them performed spoken and written narratives using a picture book titled Frog, where are you? (Mayer, 1969) containing 24 wordless pictures. The learner corpus including both 291 audio-recorded and transcribed spoken narratives and 291 written narratives was compiled. The results of the analyses showed a connection between learners’ use of plural marker -s in speaking and that in writing, while a small number of students were found to perform differently in two different tasks. Moreover, this study demonstrated support for the developmental sequence of lexical and phrasal plural marking predicted in PT.

This chapter presents part of the results of a learner corpus study to test the validity of Processability Theory (PT; Pienemann, 1998, 2005). It also addresses the issues of whether second language (L2) learners are at the same PT stages for speaking and writing. The results of the analysis of spoken and written narratives by 281 Japanese learners, focusing on the acquisition of the English plural marker ‑s on nouns, have demonstrated support for the hypothesised developmental sequence for English morphology in PT. In addition, a positive relationship has been found between the learners’ spoken and written production, suggesting that PT can legitimately be used to examine L2 writing as well as speaking.