Japanese irregular verbs


is very regular, as is usual for an agglutinative language, but there are a number of exceptions. The best-known irregular verbs are the common verbs する suru "do" and 来る kuru "come", sometimes categorized as the two Group III verbs. As these are the only significantly irregular verbs, and the only verbs frequently flagged as irregular, it is sometimes incorrectly stated that these are the only irregular verbs in Japanese, but there are in fact more, about a dozen total, depending on how one counts. The other irregular verbs encountered at the beginning level are ある aru "be " 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".

''suru'' and ''kuru''

The most significant irregular verbs are the verbs する suru "do" and 来る kuru "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 these are vowel stem conjugation, 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 kurunotes
-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 koirregular 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 koreruirregular 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 kurebaregular

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 II 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, together with the verb ある aru "be ", 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.
formaffirmative plainaffirmative politeaffirmative honorificnegative plainnegative politenegative honorific
non-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 gozaimasen
past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*		じゃないでした ja nai deshita
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 5 special polite verbs have the slight irregularity that 〜る -ru changes to 〜い -i in the -masu stem and imperative stem, 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 in 〜て/〜た -te/-ta form, most significantly 行く iku/yuku "go":
These latter euphonic changes – -ott- → -out- – 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.
Note that 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 of consonant stem 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 〜する suru verbs following a two-kanji compound are regular, behaving as a kanji noun followed by an independent verb, there is irregular behavior for single kanji suru verbs, and they behave as a single fused word, with various forms and sometimes irregular conjugation.
Firstly, these exhibit sound changes, which two-kanji suru verbs do not, yield these forms :
Secondly, the 〜る can be dropped, corresponding to the earlier す form of する, yielding:
Finally, the する／す／ず may be conjugated in various ways, particularly in less common forms. This is particularly noticeable for 愛する ai-suru, which is often conjugated as 愛す ai-su, such as the potential form being 愛せる ai-seru and the negative form being 愛さない ai-sanai.
Some single-kanji する verbs have irregular passive conjugations, stemming from classical Japanese.
For example:
For a few verbs, the root of the verb changes depending on context. Most significantly, these are:
Some verbs follow rules that are regular, but relatively unusual or special. While not irregular per se, 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 ka-wa-nai, from 買う ka-u. This is due to these traditionally having a w, but the being lost except as わ wa.

''iru'' and ''eru'' verbs

Most Japanese verbs are consonant stem, though there is also the vowel stem category. All vowel stem verbs end in -iru or -eru, but not all verbs ending in -iru or -eru are vowel stem – some are instead consonant stem. Thus the conjugation type of a verb ending in -iru or -eru cannot be determined just from the dictionary form, and which verb is which must be memorized individually.
There are about a hundred such verbs with common examples being 知る shiru "know", 走る hashiru "run", 入る hairu "enter", and 帰る kaeru "return".
There are also homophone verbs that have either a vowel stem or a consonant stem; for example, 生きる ikiru "live, stay alive" and 寝る neru "sleep" have a vowel stem, but 熱る ikiru "become sultry" and 練る neru "temper, refine, knead" have a consonant stem.

''nu'' verbs

死ぬ shinu is the only ぬ -nu verb, and thus its conjugations are less familiar, but is otherwise regular. There used to be other ぬ -nu verbs, notably 往ぬ／去ぬ いぬ inu "leave".

Compound verbs

are generally constructed using the masu stem form of the primary verb, as in 読み始める yomi-hajimeru "begin to read". In some cases compound verbs do not follow this pattern, generally due to sound change. Such exceptions include 振る舞う furu-mau "behave, conduct; treat ", from 振るう furuu + 舞う mau, instead of the regular ×振るい舞う *furui-mau.

Abbreviations

There are various abbreviations in Japanese, primarily of nouns or of inflections, such as 〜ている to 〜てる or 〜ておく to 〜とく, or even 〜ているの to 〜てん, though verb roots only rarely change. One such example is in the verb いらっしゃる, which has the following abbreviated forms:
The imperative form of the auxiliary verb 〜くれる -kureru is 〜くれ -kure, rather than the expected ×くれろ *kurero.

Adjectives

Japanese adjectives, specifically i-adjectives, function grammatically as verbs, though with more limited conjugation. There are a few irregularities of note. Most significantly, 良い yoi "good" is generally replaced by ii in the base form, though only yoi is used in conjugated forms such as 良く yoku and 良くない yokunai.
There are more minor and subtler irregularities in certain constructions, particularly in adjectives with single-mora roots. In the -me form, adjectives can replace the -i with a 〜め -me to indicate "somewhat", as in 薄め usu-me "somewhat watery, weak" from 薄い usu-i "watery, weak". However, in some cases the -i is not dropped, notably 濃いめ ko-i-me "somewhat strong ", from 濃い ko-i.
In the -sugiru form, verbs and adjective attach a 〜すぎる -sugiru to the stem to indicate "excessive" – for example 近すぎる chika-sugiru "too close", from 近い chika-i "close" – but in the case of a 〜ない -na-i negative ending, there is sometimes an intrusive 〜さ -sa, yielding 〜なさすぎる instead of the expected 〜なすぎる -na-sugiru. Typically this is optional, and generally omitted, as in 忙しな（さ）すぎる sewashina-sugiru "too restless", but for single-mora stems it is generally included, as in なさすぎる na-sa-sugiru "not too much", instead of marginal △なすぎる ?na-sugiru. There is considerable variation and uncertainty by native speakers, as these forms are uncommon. Further, this is confusingly similar to the intrusive 〜さ -sa when an adjective is followed by 〜そうだ -sō da "appears, seems", so 良さそうだ yo-sa-sō da "seems good" and 無さそうだ na-sa-sō da "seems not", but 良すぎる yo-sugiru "too good" and 無さすぎる na-sa-sugiru "too not, too absent".
Note that 静けさ shizu-ke-sa "tranquility" is not an irregular derivation of 静か shizu-ka "quiet, still" – the regular derivation 静かさ shizu-ka-sa "quietness, stillness" exists and is used – but is rather a separate word of distinct etymology – in Old Japanese the root words were 静けし shizu-ke-shi and 静かなり shizu-ka-nari, to which the 〜さ -sa was separately affixed.

History

Some irregular verbs date at least to Old Japanese, notably する、来る、ある、死ぬ. The other ぬ verb いぬ also dates to Old Japanese, though is now no longer used, and 居る iru "be " was formerly をる woru and irregular, though it is now regular.