Adjectival noun (Japanese)

In descriptions of the Japanese language, an adjectival noun, adjectival, or na adjective is a noun that can function as an adjective by taking the particle 〜な na. (In comparison, regular nouns can function adjectivally by taking the particle 〜の no, which is analyzed as the genitive case.) Adjectival nouns constitute one of several Japanese word classes that can be considered equivalent to adjectives. In their attributive function, Japanese adjectival nouns function similarly to English noun adjuncts, as in "chicken soup" or "winter coat" – in these cases, the nouns "chicken" and "winter" modify the nouns "soup" and "coat", respectively. Japanese adjectival nouns can also be used predicatively – in that use, they do not take the na suffix, but normally combine with forms of the copular verb.

In Late Old Japanese (below), a separate kind of tari adjectival nouns developed alongside the existing nari ones (nari, tari were the conclusive forms, while naru, taru were the attributive forms). The nari ones developed into the adjectival nouns (naru contracted to na, while nari was replaced by da (the copula)) that are the subject of this article, while the tari ones mostly died out over the course of Late Middle Japanese, being mostly gone by Early Modern Japanese, surviving as fossils in a few words which are generally considered somewhat stiff or archaic. These are generally referred to as ト・タル形容動詞 (to, taru keiyōdōshi) or タルト型活用 (taruto kata katsuyō – “taru, to form conjugation”), and can also function adverbially with 〜と to, instead of the 〜に ni which is mostly used with な nominals. See taru adjectives for further discussion in English, and 形容動詞#タルト型活用 for Japanese.

A few nari adjectival nouns followed a similar path to tari adjectival nouns, becoming naru adjectives in Modern Japanese (analogous to taru adjectives), rather than na adjectives as most nari adjectival nouns did. These include 単なる tannaru "mere, simple" or 聖なる seinaru "holy" and are generally classed as rentaishi.

Japanese adjectival nouns differ in etymological origin from adjectival verbs. Whereas adjectival verbs are almost entirely native in origin, the class of adjectival nouns comprises mostly foreign loanwords and a small subset of polymorphemic native words. All words listed in this section take the attributive na and predicative da copula.

The internal properties of Japanese adjectival nouns can be analysed either through a lexical features approach or through a Distributed Morphology approach.