Japanese irregular verbs

Japanese verb conjugation is very regular, as is usual for an agglutinative language, but there are a number of exceptions.

Likewise, the "regular" godan verbs tou (問う) and kou (請う) are just as irregular.

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".

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.

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.

Euphonic change also results in some conjugations being uniform across the language, but irregular compared with other verbs.

Some single-kanji する verbs have irregular passive conjugations which stem from classical Japanese.

This is due to these traditionally having a w, but the [w] being lost except as わ wa (and in を (w)o following an ん n).

There are many such verbs with common examples being 知る shiru "know", 走る hashiru "run", 入る hairu "enter", and 帰る kaeru "return".

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 (to food or drink)", from 振るう furuu + 舞う mau, instead of the regular ×振るい舞う *furui-mau.

In the -sugiru form, verbs and adjective attach a 〜すぎる -sugiru (in kanji 〜過ぎる) 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 (and standalone ない nai), there is sometimes an intrusive 〜さ -sa, yielding 〜なさすぎる (standalone なさすぎる na-sa-sugiru) instead of the expected 〜なすぎる -na-sugiru.

[7][8] 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.

The other ぬ verb いぬ also dates to Old Japanese, though is now no longer used, and 居る iru "be (animate)" was formerly をる woru and irregular, though it is now regular.