Old and Middle Japanese are the pre-modern periods of the attested history of the Japanese language. Old Japanese (OJ) is largely the language of the 8th century, with a modest, but still significant number of written sources, most of which is poetry. Middle Japanese is divided into two distinct periods, Early Middle Japanese (EMJ, 800–1200) and Late Middle Japanese (LMJ, 1200–1600). EMJ saw most of the significant sound changes that took place in the language, as well as profound influence from Chinese, whereas most grammatical changes took place between the end of EMJ and the end of LMJ. By the end of LMJ, the Japanese language had reached a form that is not significantly different from present-day Japanese. OJ phonology was simple, both in terms of phoneme inventory and syllable structure, with a total of only 88 different syllables. In EMJ, the language became quantity sensitive, with the introduction of a long versus short syllables. OJ and EMJ had obligatory verb inflection for a number of modal and syntactic categories (including an important distinction between a conclusive and an (ad)nominalizing form), whereas the expression of aspect and tense was optional. Through late EMJ and LMJ this system changed completely to one without nominalizing inflection, but obligatory inflection for tense. The morphological pronominal system of OJ was lost in EMJ, which developed a range of lexical and lexically based terms of speaker and hearer reference. OJ had a two-way (speaker–nonspeaker) demonstrative system, which in EMJ was replaced by a three-way (proximal–mesial–distal) system. OJ had a system of differential object marking, based on specificity, as well as a word order rule that placed accusative marked objects before most subjects; both of these features were lost in EMJ. OJ and EMJ had genitive subject marking in subordinate clauses and in focused, interrogative and exclamative main clauses, but no case marking of subjects in declarative, optative, or imperative main clauses and no nominative marker. Through LMJ genitive subject marking was gradually circumscribed and a nominative case particle was acquired which could mark subjects in all types of clauses. OJ had a well-developed system of complex predicates, in which two verbs jointly formed the predicate of a single clause, which is the source of the LMJ and NJ (Modern Japanese) verb–verb compound complex predicates. OJ and EMJ also had mono-clausal focus constructions that functionally were similar to clefts in English; these constructions were lost in LMJ.
The Northeast Asia is one of the unique points on the globe where there are many language isolates and portmanteau families. From a conservative point of view, the Japanese language is a member of such a portmanteau family that has recently and increasingly been called Japonic in the Western literature. While Japanese is unquestionably a member of this Japonic language family, which consists of two Japanese languages (Japanese itself and the moribund Hachijō language) and four or five relatively closely related Ryūkyūan languages (Amami, Okinawan, Miyako, Yaeyama, and possibly Yonaguni), attempts have also been made to establish a genetic relationship between Japanese and various other language families. Most of these attempts have been amateurish, a major exception being the Koreo-Japonic hypothesis, which still remains unproven as well. It is also quite likely that the Japonic language family (or, more precisely, Insular Japonic) is the only linguistic grouping whose genetic relationship can be established beyond any doubt. A genetic relationship is also likely to exist between Japonic and a number of fragmentarily attested languages that once flourished in the south and center of the Korean Peninsula, but that died out no later than 9th century A.D. The paucity of material available does not allow one to establish solid predictive-productive regular correspondences in many cases, but intuitively the genetic relationship seems to be a matter of fact. Anything beyond intuition, however, lies in the realm of conjecture and speculation. The alleged Koreo-Japonic relationship is best explained by a centuries-long contact relationship rather than by common origin, given such factors as the virtual absence of any kind of shared paradigmatic morphology, as well as by multiple problems in establishing the real (and not imaginable or made-to-fit) regular correspondences. The Japanese-“Altaic” hypothesis is even more speculative and far-fetched. Consequently, the conclusion is that the Japanese language or the Japonic language family has no demonstrable relationship with any other language family or language isolate on the planet.
In a special Focus-to-Predicate concord construction (kakari musubi), specific focus particles called kakari joshi correlate with predicate conjugational endings, or musubi, other than regular finite forms, creating special illocutionary effects, such as emphatic assertion or question. In Old Japanese, a particle ka, s(/z)ö, ya, or namu triggers an adnominal ending, while kösö calls for a realis ending. In Old Okinawan, ga or du prompts an adnominal ending, while sɨ associates with realis endings. Kakari musubi existed in Proto-Japonic but died out in the Japanese branch; however, it is still preserved in its sister branch, Ryukyuan, in the Okinawan language. This concord phenomenon, observed in only a few languages of the world, presents diverse issues concerning its evolution from origin to demise, the functional and semantic differences of its kakari particles (e.g., question-forming Old Japanese ka vs. ya) and positional (sentence-medial vs. sentence-final) contrast. Furthermore, kakari musubi bears relevance to syntactic constructions such as clefts and nominalizations. Finally, some kakari particles stemming from demonstratives offer worthy data for theory construction in grammaticalization or iconicity. Because of its far reaching relevance, the construction has garnered attention from both formal and functional schools of linguistics.