Japanese conjugation
Japanese conjugation, like the conjugation of verbs of many other languages, allows verbs to be morphologically modified to change their meaning or grammatical function. In Japanese, the beginning of a word is preserved during conjugation, while the ending of the word is altered in some way to change the meaning. Japanese verb conjugations are independent of person, number and gender ; the conjugated forms can express meanings such as negation, present and past tense, volition, passive voice, causation, imperative and conditional mood, and ability. There are also special forms for conjunction with other verbs, and for combination with particles for additional meanings.
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For Japanese verbs, the verb stem remains invariant among all conjugations. However, conjugation patterns vary according to a verb's category. For example, 知る (shiru) and 着る (kiru) belong to different verb categories (godan and ichidan, respectively) and therefore follow different conjugation patterns. As such, knowing a verb's category is essential for conjugating Japanese verbs. Japanese verbs can be allocated into three categories: Verbs are conjugated from their "dictionary form", where the final kana is either removed or changed in some way. From a technical standpoint, verbs usually require a specific conjugational stem (see § Verb bases, below) for any given inflection or suffix. With godan verbs, the conjugational stem can span all five columns of the gojūon kana table (hence, the classification as a pentagrade verb). Ichidan verbs are simpler to conjugate: the final kana, which is always る (ru), is simply removed or replaced with the appropriate inflectional suffix. This means ichidan verb stems, in themselves, are valid conjugational stems which always end with the same kana (hence, the classification as a monograde verb).
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Conjugable words (verbs, i‑adjectives, and na‑adjectives) are traditionally considered to have six possible conjugational stems or bases (活用形, katsuyōkei; literally "conjugation forms"). However, as a result of the language evolving, historical sound shifts, and the post‑WWII spelling reforms, three additional sub‑bases have emerged for verbs (seen in the table below as the Potential, Tentative, and Euphonic bases). Meanwhile, verbs no longer differentiate between the conclusive form (終止形, shūshikei; used to terminate a predicate) and the attributive form (連体形, rentaikei; used to modify a noun or noun phrase) bases (these bases are only distinguished for na‑adjectives in the modern language, see Japanese adjectives). Verb bases function as the necessary stem forms to which inflectional suffixes attach. The "default" dictionary form, or lemma, of any conjugational morpheme, be it a verb, an adjective or an auxiliary, is its conclusive form, which is listed first in the table below. The verb group (godan, ichidan, or irregular) determines how to derive any given conjugation base for the verb. With godan verbs, the base is derived by shifting the final kana along the respective vowel row of the gojūon kana table. With ichidan verbs, the base is derived by removing or replacing the final ru (る) kana.
Derivative verb bases
There are three modern verb base forms that are considered to be derived from older forms. These are the potential, hortative, and euphonic sub‑bases, as shown in the Verb base formation table above. As with all languages, the Japanese language has evolved to fulfil the contemporary needs of communication. The potential form of verbs is one such example. In Old Japanese and Early Middle Japanese, potential was expressed with the verb ending yu (ゆ), which was also used to express the passive voice ("to be done") and the spontaneous voice ("something happens on its own"). This evolved into the modern passive ending -(ra)reru (（ら）れる), which can similarly express potential and spontaneous senses. As usage patterns changed over time, different kinds of potential constructions emerged, such as the grammatical pattern of the rentaikei base + -koto ga dekiru (〜ことができる), and also via the kanōkei base. The historical development of the kanōkei base is disputed, however the consensus is that it stemmed from a shift wherein transitive verbs developed an intransitive sense similar to the spontaneous, passive, and potential, and these intransitive forms conjugated in the 下二段活用 (shimo nidan katsuyō, lower bigrade conjugation pattern) of the Classical Japanese of the time. The lower bigrade conjugation pattern evolved into the modern ichidan pattern in modern Japanese, and these stems for godan verbs have the same form as the hypothetical stems in the table above.
The bases of suru
Unlike most verbs, suru (する) and its derived compounds exhibit strong irregularity in their verb bases. In some cases, some variants are preferred over the others, and such preferences vary among speakers. Roughly speaking, there are three major groups that behave similarly: Across the following forms of suru within standard Japanese, an eastern dialect, while there is a dominance of the eastern vowel i as in shinai, shiyō and shiro, the once prestigious western vowel e, as in sen(u) and seyo, still has currency especially in formal or literary Japanese. Such variants as senai and sanai (both of shinai); shin(u) (of sen(u)); shō (← seu), seyō and sō (all of shiyō); sero (of shiro); and shiyo, sē and sei (all of seyo), remain dialectal or obsolete.
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The nucleus of a sentence, or a nuclear sentence, requires nothing more than a verb, adjective, or noun-copula phrase, to stand on its own as a complete, grammatical utterance: Notice how there are no mentions of explicit subjects or objects, whether they be nouns or pronouns, in the above examples, unlike in the possible English translations. The nucleus is the only essential part of discourse, with other information, such the subject and the object, being supplementally built on top of it: Certain Japanese particles allow what Martin (2004:316–326) harvcoltxt error: no target: CITEREFMartin2004 (help) calls "nucleus splitting." When a nucleus is split, a focus particle is inserted between its infinitive and its auxiliary, the latter of which normally either fuses with the former into a single contraction, or does not surface at all: Of focus particles, wa ("as for," "speaking of") subdues what comes before it to the background, while throwing focus onto what comes after; and mo ("even," "too") highlights and raises what comes before it to the foreground. In the following examples, the focused information is underlined in the Japanese original, and put in all caps in the English translations to emulate spoken stress:
The copulae are the basis of the nominal nucleus. It follows a noun, and means "[subject] is <noun>," similarly to the copula be in English. Certain nouns with descriptive meanings, called "adjectival nouns," can also precede a copula. Of the various forms of the copulae, nara(ba) functions as a type of evidential conditional. Darō can be added to verbs and adjectives to form the modern tentative. Desu can be used as a meaningless politeness flourish with word forms that do not readily combine with the politeness auxiliary ‑masu, such as an adjective or a negative auxiliary. The past deshita and the tentative deshō are both meaningful and polite extenders to word forms that lack any mechanism to convey pastness and tentativity, namely the western negative ‑n(u).
Copulae: Conjugation table
The copulae of Japanese demonstrate suppletion, in that they combined different forms from different words into one word. The original copulae were all based on the verb ari (あり; 'to exist'), which evolved into the modern aru (ある). It needed to be preceded by one of the three particles, ni, nite → de and to, which yielded three variants, ni ari/ni aru → nari/naru, de ari/de aru → da and to ari/to aru → tari/taru, the last of which fell out of use, but did phonetically coincide with te ari/te aru → tari/taru, which in turn evolved into the modern past auxiliary ta. It also combined with adjectival roots to expand their conjugation, for example akaku arō → akakarō (赤かろう), akaku atta → akakatta (赤かった), etc.
Copulae: Grammatical compatibility
Derived from aru and arimasu, the copulae can have all the forms that these verbs are capable of having. Certain affirmative conclusive and attributive forms have contracted, especially in speech, such as de aru → da/ja and de arimasu → desu; the negative forms remain uncontracted, meaning there is no such form as *daran or *desen.
