Japanese verb conjugation is very regular, as is usual for an agglutinative language, but there are a number of exceptions. The best-known are the common verbs する suru "do" and 来る kuru "come", sometimes categorized as the two Group 3 verbs. As these are the only verbs frequently flagged as significantly irregular, they are sometimes misunderstood to be the only irregular verbs in Japanese. However, there are about a dozen irregular verbs in Japanese, depending on how one counts. The other irregular verbs encountered at the beginning level are ある aru "be (inanimate)" and 行く iku/yuku "go", with the copula behaving similarly to an irregular verb.
There are also a few irregular adjectives, of which the most common and significant is 良い yoi "good".
Terminology The word "irregular" is tentatively used to translate the Japanese word .Kenkyusha's New Japanese-English Dictionary There are four types of : , abbreviated . This type applies to the modern verb , its classical equivalent , and all their derived compounds, such as , , , and . refers to a group of kana in the gojūon table that are headed by and all contain the consonant . English translations include "s-irregular" ("s-irr") and simply "sa-hen". , abbreviated . This type applies to the modern verb and its classical equivalent . refers to a group of kana in the gojūon table that are headed by and all contain the consonant . English translations include "k-irregular" ("k-irr") and simply "ka-hen". , abbreviated . This type applies to the classical verbs (which evolved into the "regular" modern godan verb shinu) and . refers to a group of kana in the gojūon table that are headed by and all contain the consonant . English translations include "n-irregular" ("n-irr") and simply "na-hen". , abbreviated . This type applies to the classical verbs (which evolved into the "regular" modern godan verb aru), , (modern oru) and (modern haberu). refers to a group of kana in the gojūon table that are headed by and all contain the consonant . English translations include "r-irregular" ("r-irr") and simply "ra-hen".
"Irregular verbs", or actually, henkaku verbs, are a minor group of verbs that do not conform to the inflectional patterns of major "regular" godan and ichidan verbs. This does not necessarily mean that all "regular" verbs are uniformly regular, nor that all "irregular" verbs of one of the classes above are equally irregular. For instance, the verb belongs to the "regular" godan class, yet when combining with the auxiliary or the particle , it exhibits irregularity compared to the rest of its own class. Likewise, the "regular" godan verbs and are just as irregular. Meanwhile, some "irregular" sa-hen verbs such as and have assumed many inflectional forms typical of the "regular" godan and ichidan classes, respectively, making them increasingly "regular", yet irregular to their own "irregular" prototype, .
Historically, s-irregular and k-irregular verbs were sometimes known as , given that their forms contain three out of the five vowels of Japanese.
suru and kuru
The most significant irregular verbs are the verbs する suru "to do" and 来る kuru "to come", which are both very common and quite irregular. Often the conjugations behave as if they were instead the verb しる or す, or respectively きる or こる, where (other than す) these are ichidan verb (Group 2 verbs, ru verbs) conjugation (there are no -oru ichidan verbs, though 来る sometimes behaves as if it were one), but beyond there are further exceptions. Historically する came from earlier す, which explains some of the irregularity. The following table is ordered to emphasize the regularities. form する suru 来る kuru notes-masu stem し shi 来 ki しる and きる-te form して shite 来て kite しる and きる-ta form した shita 来た kita しる and きる-nai form しない shinai 来ない konai しる and こる-nai stem せ se 来 ko irregular and こる Volitional しよう shiyō 来よう koyō しる and こる Passive される sareru 来られる korareru す and こる Causative させる saseru 来させる kosaseru す and こる Potential できる dekiru 来られる korareru, 来れる koreru suppletive and こる Imperative しろ shiro, せよ seyo 来い koi しる、す and irregular Conditional すれば sureba 来れば kureba regular
The irregular 〜ない -nai stem of する is often overlooked; it is used in grammatical forms where the 〜ない form is used without the 〜ない – generally formal – as in 食べず tabe-zu "without eating" or 食べんがため tabe-n ga tame "for the purpose of eating". In these contexts する becomes せ, as in せず se-zu "without doing" or せんがため se-n ga tame "for the purpose of doing". Note the similarity to 〜ません as the negative form of 〜ます, of the same origin.
The potential 来れる koreru form is from the omission of ra in the られる rareru potential form, and is found in all Group 2 verbs; it is considered an error by prescriptive grammarians, but is increasingly common, particularly in spoken speech and in younger Japanese.
Basic grammar
The copula だ and です (polite), together with the verb ある aru "be (inanimate)", which is used grammatically, and the 〜ます suffix, which functions similarly to an irregular auxiliary verb, are all irregular to varying degrees, and particularly used in polite speech. It is debatable whether they should be classified as verbs or as different parts of speech.
Formally, the copula is である de aru. This form is normal in writing, but in spoken Japanese it is almost universally contracted to だ da, or in some dialects じゃ ja or や ya. When conjugated politely, である de aru becomes であります de arimasu following the regular transformation. This form is normal in writing, except that most writing either uses plain conjugations or the honorific forms, so in fact this form is not commonly seen. In spoken Japanese, であります de arimasu is universally contracted to です desu.
form affirmative plain affirmative polite affirmative honorific negative plain negative polite negative honorificnon-past だ daである de aru*じゃ ja** です desuであります de arimasu* でございます de gozaimasu じゃない ja naiではない dewa nai* じゃないです ja nai desuじゃありません ja arimasenではありません dewa arimasen* でございません de gozaimasenpast だった dattaであった de atta* でした deshitaでありました de arimashita* でございました de gozaimashita じゃなかった ja nakattaではなかった dewa nakatta* じゃなかったです ja nakatta desuじゃありませんでした ja arimasendeshitaではありませんでした dewa arimasendeshita* でございませんでした de gozaimasendeshita-te form で de で deであって de atte* で deであって de atte* じゃなくて ja nakuteではなくて dewa nakute* じゃなくて ja nakuteではなくて dewa nakute* ではなくて dewa nakute
(*) indicates literary forms
(**) じゃ ja is a dialectal spoken form of だ da
Polite verbs
These five special polite verbs have the slight irregularity that 〜る -ru changes to 〜い -i in the -masu stem (continuative form, 連用形) and imperative stem (命令形), as opposed to the expected ×〜り *-ri and ×〜れ *-re. As these all end in -aru, these can be termed "aru special class". The most commonly encountered of these is 〜ください, used for polite requests.
base form -masu formいらっしゃる いらっしゃいますおっしゃる おっしゃいますくださる くださいますござる ございますなさる なさいます
Euphony A few short verbs have irregular euphonic form (音便形) in 〜て/〜た -te/-ta form, most significantly 行く iku "go": 行く iku conjugates to 行って itte and 行った itta, not ×いいて *iite or いいた *iita 問う・訪う tou "ask; visit, call on" conjugates to 問うて・訪うて toute, not *totte 請う・乞う kou "request; beg" conjugates to 請うて・乞うて koute, not *kotte 恋う kou "miss, yearn, pine" conjugates to 恋うて koute, not *kotte These latter euphonic changes – -owit- → -owt- → -out- (→ -ōt-) – are regular in -te/-ta form in Kansai dialect, e.g., しまった shimatta "done it; darn" → しもうた shimōta, but only occur in the above exceptions in standard Japanese.
Euphonic change also results in some conjugations being uniform across the language, but irregular compared with other verbs. Most significantly, the た ta and て te forms (perfective and participle/gerundive) of godan verbs all exhibit euphonic sound change, except for す su verbs.
The volitional form, as in 読もう yomō and 食べよう tabeyō, does not correspond to a verb stem ending in -o but is actually formed from the irrealis -a stem, with a euphonic change of a to o – for example yomu > yoma-u > yomou = yomō. Thus the apparent volitional "stem" is not seen in other contexts.
Single kanji suru While pronunciation remains unchanged when two-kanji compounds are denominalized by 〜する suru verbs, pronunciation or conjugations may be irregular in the cases where single-kanji suru verbs behave as new independent words.
For example, these single-kanji words exhibit various pronunciation changes (where two-kanji suru verbs would not): 愛する ai-suru – no sound change 達する tas-suru – gemination (促音) from たつ+する tatsu+suru to たっする tas-suru 禁ずる kin-zuru – voicing (連濁 rendaku) from きん+する kin+suru to きんずる kin-zuru 禁じる kin-jiru – -zuru verbs have an associated -jiru form, which is the more common form in modern Japanese
Additionally, the 〜る can be dropped accordingly (except for the 〜じる forms): 愛す ai-su 達す tas-su 禁ず kin-zu
These する／す／ず forms may be conjugated in various ways, particularly in less common forms. One notable example is 愛する ai-suru (often conjugated as 愛す ai-su) where the potential form is 愛せる ai-seru rather than 愛できる ai-dekiru,What is a suru verb?, sci.lang.japan FAQ and the negative form is 愛さない ai-sanai rather than 愛しない ai-shinai. While irregular compared to the -suru conjugation scheme, 愛す ai-su and other -su verbs are actually conjugated as regular Godan (Group 1) verbs. Similarly, the -jiru verbs mentioned above are conjugated as regular Ichidan (Group 2) verbs.
Some single-kanji する verbs have irregular passive conjugations which stem from classical Japanese.
For example: 罰する becomes 罰せられる not 罰される 発する becomes 発せられる not 発される
Alternative roots For a few verbs, the root of the verb changes depending on context. Most significantly, these are: 〜得る -uru – auxiliary verb to indicate possibility, the u changes to e in the negative and polite forms, yielding 〜得る 〜うる -uru "... possible", 〜得ない 〜えない -enai "...impossible", and 〜得ます 〜えます -emasu "... possible (polite)". This is often written in kana, and is most familiar from ありうる ariuru "be possible" and ありえない arienai "be impossible". 行く iku, yuku "go" – some dialectal differences, but generally iku by itself and -yuki when used as a suffix, e.g., for train destinations. There is some dialectal difference here as well, with iku as more standard, but yuku common in Western Japan (as well as song lyrics). By contrast, 言う iu, yuu "say" is only a dialectal difference, with standard iu, but Western Japanese yuu.
Regular but unusual Some verbs follow rules that are regular (in terms of the overall language), but relatively unusual or special. While not irregular by itself, they present many of the same difficulties.
Irrealis form of u verbs Verbs ending in う -u have the unusual irrealis ending -wa, as in 買わない from 買う . This is due to these traditionally having a w, but the [w] being lost except as わ wa (and in を following an ん n).
iru and eru verbs
Most Japanese verbs are , though there are also the . All ichidan verbs end in -iru or -eru, but not all verbs ending in -iru or -eru are ichidan verbs – instead, some are godan verbs. Thus the conjugation type of a verb ending in -iru or -eru cannot be determined naively from the dictionary form.
There are many such verbs with common examples being 知る "know", 走る "run", 入る "enter", and 帰る "return".
There are also homophone verbs that could be either godan or ichidan verbs; for example, 生きる "live, stay alive" and 寝る "sleep" are ichidan verbs, but 熱る "become sultry" and 練る "temper, refine, knead" are godan verbs.
nu verbs 死ぬ (to die) is the only ぬ -nu verb, and thus its conjugations are less familiar, but it is otherwise regular. There used to be other ぬ -nu verbs, notably 往ぬ／去ぬ いぬ "leave".
Compound verbs