i-adjectives are considered verbs because they inflect with the same bases as verbs and their respective usages: irrealis (未然形 mizenkei), continuative (連用形 renyōkei), terminal (終止形 shuushikei), attributive (連体形 rentaikei), hypothetical (仮定形 kateikei), and imperative (命令形 meireikei).
Among the six bases of verbs for i-adjectives, there exist two sets of inflection paradigms: a "plain" or "true" conjugation, and what is known as a kari-conjugation (カリ活用 kari-katsuyō), which is the result of the contraction between the "plain" continuative form 〜く (ku) and the verb あり (有り, 在り) ari, meaning "to exist", "to have", or "to be".
The distinction, although no longer meaningful in pronunciation, is still reflected by the writing system, where し is still written out in hiragana, as in atarashii (新しい, new).
[1][better source needed] In some cases the original word is now only used (or almost always used) in the 〜やか form, such as 鮮やか (aza-yaka, "vivid, brilliant"), 穏やか (oda-yaka, "calm, gentle"), and 爽やか (sawa-yaka, "fresh, clear"), while in other cases the word is used in isolation, such as 雅 (miyabi, "elegant, graceful"), which is used alongside 雅やか (miyabi-yaka, "elegant, graceful"), and in other cases a related word also exists, such as 賑やか (nigi-yaka, "bustling, busy") and the verb 賑わう (nigi-wau, "be bustling, be busy").
These are generally less subjective, but declined in popularity relative to the 〜やか construction in the Heian period[1][better source needed] Notable examples include 明らか (aki-raka, "clear, obvious") and 柔らか／軟らか (yawa-raka, "soft, gentle").
but the form mostly died out; the remaining taru-adjectives are fossils, and conjugationally defective, having formerly held the pattern of the r-irregular class, like its component あり.
There are also a few naru-adjectives such as 単なる (tannaru, "mere, simple") or 聖なる (seinaru, "holy"), which developed similarly to taru-adjectives.
For example, ano (あの, "that") can be analysed as a noun or pronoun あ (a) plus the genitive ending の (no); aru (ある or 或る, "a certain"), saru (さる, "a certain"), and iwayuru (いわゆる, "so-called") can be analysed as verbs (iwayuru being an obsolete passive form of the verb iu (言う) "to speak"); and ōkina (大きな, "big") can be analysed as the one remaining form of the obsolete adjectival noun ōki nari.
The final form onaji, which occurs with the copula, is usually considered to be a noun, albeit one derived from the adjectival verb.
Everyday examples notably include yoshi (良し, good, ok) and nashi (無し, nothing) – in modern grammar yoi (良い) and nai (無い), respectively.
です is added directly after the inflected plain form and has no syntactic function; its only purpose is to make the utterance more polite (see Honorific speech in Japanese).
In present tense, it is read as いい (ii), but since it derives from よい (yoi), all of its inflections supplete its forms instead.
The imperative form is rarely used outside of set expressions; a common usage is once again with 良い (yoi), and its imperative form 良かれ (yokare), in idiomatic set expressions like 良かれと思う (yokare to omou, to wish for the best, to have good intentions) or 良かれ悪しかれ (yokare-ashikare, good or bad, for better or for worse, be it good or bad), also making use of the imperative form of 悪しい (ashii, (formerly the regular word for "bad", since replaced by 悪い (warui))).
The imperative form of 無い (nai), 無かれ (nakare), is also used in archaic speech to indicate prohibition or a command not to do something or to indicate that one must not do something (also spelled 勿れ, 毋れ, 莫れ).
na-adjectives have a basic inflection created by dropping the 〜な (-na) and replacing it with the appropriate form of the verb だ (da), the copula.
The 〜なる (naru) attributive form exists as a fossil from the archaic ナリ活用 (nari katsuyō), or nari-conjugation, the precursor to the modern na-adjective.
Generally only the 〜な (na) form is used for attribution, but the 〜なる (naru) form may be used to add a sense of stress, intensity, profundity, formality, or an imitation of archaic speech, such as 人類の偉大なる遺産 (jinrui no idai-naru isan, "the great legacy of humanity"), as compared to 人類の偉大な遺産 (jinrui no idai-na isan).
Generally, to express past or negative forms, additional other words or syntax are added to the sentence rather than using the full verb paradigm.
Generic words like 物 (mono), 事 (koto), 人 (hito), and 方 (kata) are used as fill-ins with the attributive form instead.
In the case of i-adjectives, い (i) changes to く (ku): and in the case of na-adjectives, な (na) changes to に (ni): There are also some words like たくさん (takusan) and 全然 (zenzen) that are adverbs in their root form: In a few cases, a 〜に (ni) form of a word is common while a 〜な (na) form is rare or non-existent, as in 誠に (makoto-ni, "sincerely") – 誠 (makoto, "sincerity") is common, but ×誠な (*makoto-na, "sincere") is generally not used.
Because the widespread study of Japanese is still relatively new in the Western world, there are no generally accepted English translations for the above parts of speech, with varying texts adopting different sets, and others extant not listed above.
The current terms as accepted in schools (see w:ja:学校文法) for adjectival words are keiyōshi (形容詞) and keiyō dōshi (形容動詞).
'form' or 'figure' or 'appearance' or 'description') refers to the semantic aspect of these words as qualifying the state or condition of a "noun;" and dōshi (動詞, lit.
However, a few, under the influence of European grammatical traditions, deviated from this norm and considered these so-called "adjectives" a subclass of dōshi.
In sum, currently: Note that some so-called "naru-adjectives" and all "taru-adjectives" were keiyō dōshi in classical Japanese where they were conjugative (inu-wa sei-nari (犬は聖なり, lit.
'calm dog')), but they are rentaishi in modern Japanese where only their attributive forms survived (sei-naru inu (聖なる犬, lit.