Contributions of the study of Japanese as a second language to our general understanding of second language acquisition and the definition of second language acquisition research

Japanese has figured frequently in second language acquisition (SLA) research, but more often than not it appears as the first language (L1) rather than the target. In this article, first I discuss the problems addressed and the insights obtained in these studies. I then consider two issues. One is what the field of SLA research should include. I suggest that it should include two categories, namely Core SLA Research, where second language (L2) linguistic knowledge is investigated, and Broad SLA research, where researchers study factors that influence the development of L2 knowledge. The other issue is what we can expect in Core SLA research concerning the L2 acquisition of Japanese. This article illustrates how studies of the L2 acquisition of Japanese can contribute to our understanding of SLA.