This paper discusses the necessity of the re-establishment of the reciprocal relationship between the study of Japanese grammar and the teaching of Japanese as a second language. Descriptive study of Japanese grammar has been developing to meet the demand of Japanese learners and teachers. However, the relationship between the two is much less close recently. Based on many examples, we will argue (1) that the descriptive study of Japanese grammar, which is said to be making less progress these days, could obtain many vital points of description from the Japanese learners' point of view, and (2) that numerous findings of the grammatical studies of several decades, on the other hand, remain unapplied to the grammatical explanations for Japanese learners.本論文は，台湾日語教育学会（2011年11月25日，静宜大学），日本語教育学会研究集会（2013年8月31日，京都外国語大学），韓国日語教育学会第28回国際学術大会（2015年12月5日，同徳大学）において同名の題目で行った講演の内容に加筆・修正を加えたものである。