Japanese syntax has also remained relatively stable, maintaining its characteristic subject–object–verb (SOV) sentence structure. A notable change in that domain is the obliteration of the distinction between the conclusive form—the finite form that concludes a sentence—and the noun-modifying form exhibited by certain predicates. For example, in early Japanese otsu and tsuyoshi were conclusive forms, respectively, of the verb ‘to drop’ and the adjective ‘to be strong.’ When these words were used as noun modifiers, the forms were inflected as otsuru, tsuyoki. The distinction between conclusive forms and noun-modifying forms played an important role in the phenomenon of syntactic concord that, for example, called for the noun-modifying forms of predicate even in concluding the predication when a subject or some other word was marked by particles such as the emphatic zo or the interrogative ka or ya. That system of syntactic concord deteriorated in Middle Japanese, and the distinction between the conclusive forms and the noun-modifying forms was also lost, the latter dominating the former. Such modern forms as ochiru ‘to drop’ and tsuyoi ‘to be strong’ are the descendants of the earlier noun-modifying forms.
A single most important development in the history of Japanese is the acquisition of the nativized writing systems that took place between the 8th and the 10th centuries. The Japanese vocabulary has been constantly enriched by loanwords—from Chinese in earlier times and from European languages in more recent history.