Classical Japanese refers to the literary Japanese of the Heian period and later, roughly the ninth through nineteenth centuries, grammatically distinct from Modern Japanese in verb conjugation, particle usage and vocabulary, and functioning as Japan's dominant literary standard for religious, courtly and scholarly writing for roughly a millennium before Meiji-era language reform brought written Japanese closer to the modern spoken vernacular. Classical Japanese belongs, like its modern descendant, to the small Japonic language family, and it is the language in which Kukai, founder of the Shingon school of esoteric Japanese Buddhism, composed his major ninth-century theological and doctrinal works after studying esoteric Buddhism in Tang dynasty China, works that established much of the terminology and conceptual framework subsequently used across Japanese esoteric Buddhist practice, including the Godai, the five great elements central to Shingon cosmology and ritual visualization.
Classical Japanese also carries the language of norito, formal Shinto ritual prayers whose archaic grammatical register remains distinct even from other Classical Japanese literary genres. Classical Japanese also underlies waka and other classical poetic forms composed by Buddhist monks and courtiers alike, a body of literature scholars mine for evidence of how Heian-period religious sentiment, especially Pure Land Buddhist anxiety about impermanence, shaped mainstream aesthetic and literary culture well beyond narrowly doctrinal Buddhist writing.