Abstract
This paper reviews the previous studies on important topics in Japanese historical phonology, introducing both classic works and newer publications. The paper then points out some of the significant issues requiring further elaboration, e.g., (1) distinctive features of /g, z, d, b/ in Old Japanese (OJ), (2) historical development of Modern Japanese /h/, (3) merging process of */di/ vs. */zi/ and */du/ vs. */zu/, (4) phonotactic constraints avoiding hiatus or word-initial /g, z, d, b, r/ in OJ. The reasons why these topics represent particularly important questions, especially with regard to the phonetic naturalness of sound change, are then explored.
