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 ãÂÂã suru "do" and æÂ¥ã 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 ãÂÂã aru "be (inanimate)" and è¡Âã 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 è¯ã yoi "good".
The word "irregular" is tentatively used to translate the Japanese word . There are four types of :
"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.
The most significant irregular verbs are the verbs ãÂÂã suru "to do" and æÂ¥ã kuru "to come", which are both very common and quite irregular. Often the conjugations behave as if they were instead the verb ãÂÂã or ãÂÂ, or respectively ãÂÂã or ãÂÂãÂÂ, where (other than ãÂÂ) these are ichidan verb (Group 2 verbs, ru verbs) conjugation (there are no -oru ichidan verbs, though æÂ¥ã sometimes behaves as if it were one), but beyond there are further exceptions. Historically ãÂÂã came from earlier ãÂÂ, which explains some of the irregularity. The following table is ordered to emphasize the regularities.
The irregular ãÂÂãªã -nai stem of ãÂÂã is often overlooked; it is used in grammatical forms where the ãÂÂãªã form is used without the ãÂÂãªã â generally formal â as in é£Âã¹ã tabe-zu "without eating" or é£Âã¹ãÂÂãÂÂãÂÂã tabe-n ga tame "for the purpose of eating". In these contexts ãÂÂã becomes ãÂÂ, as in ãÂÂã se-zu "without doing" or ãÂÂãÂÂãÂÂãÂÂã se-n ga tame "for the purpose of doing". Note the similarity to ãÂÂã¾ãÂÂã as the negative form of ãÂÂã¾ãÂÂ, of the same origin.
The potential æÂ¥ãÂÂã koreru form is from the omission of ra in the ãÂÂãÂÂã 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.
The copula ã and ã§ã (polite), together with the verb ãÂÂã aru "be (inanimate)", which is used grammatically, and the ãÂÂã¾ã 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 ã§ãÂÂã de aru. This form is normal in writing, but in spoken Japanese it is almost universally contracted to ã da, or in some dialects ãÂÂã ja or ã ya. When conjugated politely, ã§ãÂÂã de aru becomes ã§ãÂÂãÂÂã¾ã 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, ã§ãÂÂãÂÂã¾ã de arimasu is universally contracted to ã§ã desu.
(*) indicates literary forms
(**) ãÂÂã ja is a dialectal spoken form of ã da
These 5 special polite verbs have the slight irregularity that ãÂÂã -ru changes to ãÂÂã -i in the -masu stem (continuative form, é£ç¨形) and imperative stem (å½令形), as opposed to the expected ÃÂãÂÂã *-ri and ÃÂãÂÂã *-re. As these all end in -aru, these can be termed "aru special class". The most commonly encountered of these is ãÂÂãÂÂã ãÂÂãÂÂ, used for polite requests.
A few short verbs have irregular euphonic form (é³便形) in ãÂÂã¦/ãÂÂã -te/-ta form, most significantly è¡Âã iku "go":
These latter euphonic changes â -owit- â -owt- â -out- (â -à Ât-) â are regular in -te/-ta form in Kansai dialect, e.g., ãÂÂã¾ã£ã shimatta "done it; darn" â ãÂÂãÂÂãÂÂã shimà Âta, 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 ã ta and 㦠te forms (perfective and participle/gerundive) of godan verbs all exhibit euphonic sound change, except for ã su verbs.
The volitional form, as in èªÂãÂÂã yomà  and é£Âã¹ãÂÂã tabeyà Â, 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 â for example yomu > yoma-u > yomou = yomà Â. Thus the apparent volitional "stem" is not seen in other contexts.
While pronunciation remains unchanged when two-kanji compounds are denominalized by ãÂÂãÂÂã 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):
Additionally, the ãÂÂã can be dropped accordingly (except for the ãÂÂãÂÂã forms):
These ãÂÂãÂÂï¼ÂãÂÂï¼Âã forms may be conjugated in various ways, particularly in less common forms. One notable example is æÂÂãÂÂã ai-suru (often conjugated as æÂÂã ai-su) where the potential form is æÂÂãÂÂã ai-seru rather than æÂÂã§ãÂÂã ai-dekiru, and the negative form is æÂÂãÂÂãªã ai-sanai rather than æÂÂãÂÂãªã ai-shinai. While irregular compared to the -suru conjugation scheme, æÂÂã 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 ãÂÂã verbs have irregular passive conjugations which stem 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 (in terms of the overall language), but relatively unusual or special. While not irregular by itself, they present many of the same difficulties.
Verbs ending in ã -u have the unusual irrealis ending -wa, as in è²·ãÂÂãªã from è²·ã . This is due to these traditionally having a w, but the [w] being lost except as ã wa (and in ã following an ã n).
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 â 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 çÂ¥ã "know", èµ°ã "run", å ¥ã "enter", and 帰ã "return".
There are also homophone verbs that could be either godan or ichidan verbs; for example, çÂÂãÂÂã "live, stay alive" and å¯Âã "sleep" are ichidan verbs, but ç±ã "become sultry" and ç·´ã "temper, refine, knead" are godan verbs.
æÂȋ¬ (to die) is the only 㬠-nu verb, and thus its conjugations are less familiar, but it is otherwise regular. There used to be other 㬠-nu verbs, notably å¾Âã¬ï¼ÂÃ¥Âȋ¬ ãÂÂ㬠"leave".
Japanese compound verbs are generally constructed using the stem form of the primary verb, as in èªÂã¿å§ÂãÂÂã "begin to read". In some cases compound verbs do not follow this pattern, generally due to sound change. Such exceptions include æ¯ãÂÂèÂÂã "behave, conduct; treat (to food or drink)", from æ¯ãÂÂã + èÂÂã , instead of the regular ÃÂæ¯ãÂÂãÂÂèÂÂã *.
There are various abbreviations in Japanese, primarily of nouns or of inflections, such as ãÂÂã¦ãÂÂã to ãÂÂã¦ã or ãÂÂã¦ãÂÂã to ãÂÂã¨ãÂÂ, or even ãÂÂã¦ãÂÂãÂÂã® to ãÂÂã¦ãÂÂ, though verb roots only rarely change. One such example is in the verb ãÂÂãÂÂã£ãÂÂãÂÂãÂÂ, which has the following abbreviated forms:
The imperative form of the auxiliary verb ãÂÂãÂÂãÂÂã is ãÂÂãÂÂã , rather than the expected ÃÂãÂÂãÂÂã *.
Japanese adjectives, specifically i-adjectives, function grammatically as verbs, though with more limited conjugation. There are a few irregularities of note. Most significantly, è¯ã "good" is generally replaced by ii in the base form ( is found in formal usage), though only is used in conjugated forms such as è¯ã and è¯ãÂÂãªã .
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 ãÂÂã -me (in kanji ãÂÂç®) to indicate "somewhat", as in èÂÂã "somewhat watery, weak" from èÂÂã "watery, weak". However, in some cases the -i is not dropped, notably æ¿ÂãÂÂã "somewhat strong (tea etc.)", from æ¿ÂãÂÂ
In the form, verbs and adjective attach a ãÂÂãÂÂãÂÂã (in kanji ãÂÂéÂÂãÂÂãÂÂ) to the stem to indicate "excessive" â for example è¿ÂãÂÂãÂÂã "too close", from è¿Âã "close" â but in the case of a ãÂÂãªã -na-i negative ending (and standalone ãªã ), there is sometimes an intrusive ãÂÂã -sa, yielding ãÂÂãªãÂÂãÂÂãÂÂã (standalone ãªãÂÂãÂÂãÂÂã ) instead of the expected ãÂÂãªãÂÂãÂÂã Typically this is optional, and generally omitted, as in å¿ÂãÂÂãªï¼ÂãÂÂï¼ÂãÂÂãÂÂã "too restless", but for single-mora stems it is generally included, as in ãªãÂÂãÂÂãÂÂã "not too much", instead of marginal â³ãªãÂÂãÂÂã ?. There is considerable variation and uncertainty by native speakers, as these forms are uncommon. Further, this is confusingly similar to the intrusive ãÂÂã -sa when an adjective is followed by ãÂÂãÂÂãÂÂã -sà  da "appears, seems", so è¯ãÂÂãÂÂãÂÂã "seems good" and ç¡ãÂÂãÂÂãÂÂã "seems not", but è¯ãÂÂãÂÂã "too good" and ç¡ãÂÂãÂÂãÂÂã na-sa-sugiru "too not, too absent".
éÂÂãÂÂã "tranquility" is not an irregular derivation of éÂÂã "quiet, still" â the regular derivation éÂÂãÂÂã "quietness, stillness" exists and is used â but is rather a separate word of distinct etymology â in Old Japanese the root words were éÂÂãÂÂã shizu-ke-shi and éÂÂãÂÂãªã shizu-ka-nari, to which the ãÂÂã -sa was separately affixed.
Some irregular verbs date at least to Old Japanese, notably ãÂÂãÂÂãÂÂæÂ¥ãÂÂãÂÂãÂÂãÂÂãÂÂæÂȋ¬. The other 㬠verb ãÂÂ㬠also dates to Old Japanese, though is now no longer used, and å± ã "be (animate)" was formerly ãÂÂã and irregular, though it is now regular.