The rigor and intensity of investigation on Japanese in modern linguistics has been particularly noteworthy over the past 50 years. Not only has the elucidation of the similarities to and differences from other languages properly placed Japanese on the typological map, but Japanese has served as a critical testing area for a wide variety of theoretical approaches. Within the sub-fields of Japanese phonetics and phonology, there has been much focus on the role of mora. The mora constitutes an important timing unit that has broad implications for analysis of the phonetic and phonological system of Japanese. Relatedly, Japanese possesses a pitch-accent system, which places Japanese in a typologically distinct group arguably different from stress languages, like English, and tone languages, like Chinese. A further area of intense investigation is that of loanword phonology, illuminating the way in which segmental and suprasegmental adaptations are processed and at the same time revealing the fundamental nature of the sound system intrinsic to Japanese. In morphology, a major focus has been on compounds, which are ubiquitously found in Japanese. Their detailed description has spurred in-depth discussion regarding morphophonological (e.g., Rendaku—sequential voicing) and morphosyntactic (e.g., argument structure) phenomena that have crucial consequences for morphological theory. Rendaku is governed by layers of constraints that range from segmental and prosodic phonology to structural properties of compounds, and serves as a representative example in demonstrating the intricate interaction of the different grammatical aspects of the language. In syntax, the scrambling phenomenon, allowing for the relatively flexible permutation of constituents, has been argued to instantiate a movement operation and has been instrumental in arguing for a configurational approach to Japanese. Japanese passives and causatives, which are formed through agglutinative morphology, each exhibit different types: direct vs. indirect passives and lexical vs. syntactic causatives. Their syntactic and semantic properties have posed challenges to and motivations for a variety of approaches to these well-studied constructions in the world’s languages. Taken together, the empirical analyses of Japanese and their theoretical and conceptual implications have made a tremendous contribution to linguistic research.
The word accent system of Tokyo Japanese might look quite complex with a number of accent patterns and rules. However, recent research has shown that it is not as complex as has been assumed if one incorporates the notion of markedness into the analysis: nouns have only two productive accent patterns, the antepenultimate and the unaccented pattern, and different accent rules can be generalized if one focuses on these two productive accent patterns. The word accent system raises some new interesting issues. One of them concerns the fact that a majority of nouns are ‘unaccented,’ that is, they are pronounced with a rather flat pitch pattern, apparently violating the principle of obligatoriness. A careful analysis of noun accentuation reveals that this strange accent pattern occurs in some linguistically predictable structures. In morphologically simplex nouns, it typically tends to emerge in four-mora nouns ending in a sequence of light syllables. In compound nouns, on the other hand, it emerges due to multiple factors, such as compound-final deaccenting morphemes, deaccenting pseudo-morphemes, and some types of prosodic configurations. Japanese pitch accent exhibits an interesting aspect in its interactions with other phonological and linguistic structures. For example, the accent of compound nouns is closely related with rendaku, or sequential voicing; the choice between the accented and unaccented patterns in certain types of compound nouns correlates with the presence or absence of the sequential voicing. Moreover, whether the compound accent rule applies to a certain compound depends on its internal morphosyntactic configuration as well as its meaning; alternatively, the compound accent rule is blocked in certain types of morphosyntactic and semantic structures. Finally, careful analysis of word accent sheds new light on the syllable structure of the language, notably on two interrelated questions about diphthong-hood and super-heavy syllables. It provides crucial insight into ‘diphthongs,’ or the question of which vowel sequence constitutes a diphthong, against a vowel sequence across a syllable boundary. It also presents new evidence against trimoraic syllables in the language.