The Japanese language has two types of regular verbs that involve the stem, and can be referred to as Japanese consonant and vowel verbs.
Contents
Verb groups
The two groups of verbs are:
- consonant-stem, godan-katsuyō (五段活用?, "5-class conjugation"), Group I, or -u verbs; and
- vowel-stem, ichidan-katsuyō (一段活用?, "1-class conjugation"), Group II, or -ru verbs.
Most verbs are consonant-stem, but vowel-stem verbs are also common, hence the numbering "Group I" (consonant-stem, more common) and "Group II" (vowel-stem, less common). Sometimes categorization is expanded to include "Group III" (special cases) for the irregular verbs する suru and 来る kuru; note however that there are other Japanese irregular verbs, though they are generally only slightly irregular.
Consonant-stem verbs end in -u (-au, -iu, -uu, -ou), -ku, -gu, -su, -tsu, -nu, -bu, -mu or -ru, but not -eu, -zu, -dzu, -fu, -pu, or the defective columns -yu or -wu.
All vowel-stem verbs end in either -iru or -eru. However, not all verbs ending in -iru or -eru are vowel-stem verbs; for example, hashiru, "run", is a consonant-stem verb. Verbs ending in -aru, -uru and -oru also exist, and are all consonant-stem.
The Japanese names ("5-class" and "1-class") are based on the number of vowel suffixes used to form verb roots for conjugations. Classical Japanese had more verb groups (such as 2-class and 4-class) which are archaic in Modern Japanese.
Conjugation
Consonant-stem verbs conjugate differently from the vowel-stem verbs. Consonant-stem verbs conjugate after a consonant, and vowel-stem verbs conjugate after a vowel, as can be seen in the following examples:
- Note that colloquially the ら ra is dropped meaning these two become mireru and tabereru.
- Can also be written as mi.eru. The difference is like the difference between "can see" and "can be seen." Two consonant-stems that are also irregular are ik.eru/ik.areru ("can go") and kik.eru/kik.oeru ("can hear"). Other irregular verbs are suru->dekiru ("can do") and kuru->korareru ("can come").
Consonant-stem verbs ending in -u (-au, -iu and -ou) may not appear to conjugate "after a consonant"; for example, the polite form of kau (買う, "buy") is kaimasu (ka.u → ka.imasu). However, the stem is in these cases technically considered to end in the consonant w. The w is normally suppressed, but surfaces in the negative form, as in kaw.anai ("does not buy"). Traditionally these verbs ended in -hu, which is still seen on occasion in historical kana usage, and thus unambiguously ended in h.
Terminology
The terms "consonant-stem" and "vowel-stem" come from considering the invariant part of the verb (the verb stem) on the basis of phonemes – concretely, by writing in rōmaji. This is an abstract perspective, as the consonant stem itself never occurs independently, but only with a following vowel, as Japanese words are formed of morae – concretely, writing in kana. For example, while the stem of yomu is yom-, the bare *yom is not an independent word.
The standard Japanese terms, ichidan and godan, literally "one row" and "five rows", more formally monograde and pentagrade, correspond to the number of different morae (kana) that appear in the stem forms of the verb, which are then optionally combined with a suffix to form a conjugated word. Formally, verbs are classified by which column of the gojūon their stem ends in, with vowel stem verbs further distinguished into i and e type. For example, 読む yomu is of マ行五段活用 ma-gyō go-dan katsuyō "ma-column five-row conjugation" type, as its stem form end in each of the five rows of the ま column, namely まみむめも:
Note that the volitional o stem is historically the negative a stem with euphonic sound change – and the o stem is only used for the volitional form – so these verbs were traditionally called 四段 yodan "four-row, tetragrade", omitting the o form.
While the above uses are the most common uses of the respective stems, they are used in various other ways, particularly the i stem – for example 読み物 yomi-mono "reading material"; compare 食べ物 tabe-mono "food" for vowel stem.
By contrast, vowel stem verbs have a single stem form, ending either in i or e, accordingly as -iru or -eru. These are referred to respectively as 上一段 kami ichi-dan "upper one-row" and 下一段 shimo ichi-dan "lower one-row", due to i being above e in the aiueo vowel ordering. In full terminology, the column of the final kana is also listed. For 見る みる miru is of マ行上一段活用 ma-gyō kami ichidan katsuyō "ma-column upper one-row conjugation" type and has stem:
while 食べる たべる taberu is of バ行下一段活用 ba-gyō shimo ichidan katsuyō "ba-column lower one-row conjugation" and has stem:
In Japanese dictionaries, in the readings of conjugable words the stem and the inflectional suffix are separated by a dot (・), as in 赤い あか・い aka.i "red". This is used to distinguish verb type, with consonant stem verbs having only the last kana treated as suffix, while in vowel stem verbs the last two kana are treated as suffix. The column 行 of the conjugation form corresponds to the kana immediately after the dot. For example:
Note that for one-row verbs with only two kana, the entire verb is treated as a suffix, and no dot is displayed, as it would appear before the word. For example:
The terms "Group I", "Group II", and "Group III" are primarily used in Japanese language education, and may be notated as (I), (II), (III) next to a verb. Similarly, the terms "u verb" (う verb) and "ru verb" (る verb) are educational terms, and may be notated as （う） or （る）.
General
Vowel-stem verbs, such as ⾒る miru "to see" and 食べる taberu "to eat," end either in -iru or -eru (there are no other basic-form endings for this group), so most verbs ending in -iru and -eru are vowel stem verbs, but some consonant-stem verbs have these endings, too (e.g. 散る chiru "to scatter," 抓める tsumeru "to pinch"), and there are also "homophone verbs" that have either a vowel stem or a consonant stem (e.g. ikiru vowel 生きる "to live, to stay alive," consonant 熱る "to become sultry"; shimeru vowel 閉める "to close [something]," consonant 湿る "to be damp").
A rule of thumb: If the vowel i/e of the ending -iru/-eru is part of a kanji (as in 契る chigi-ru "to pledge" and 嘲る azake-ru "to ridicule"), chances are high that the verb has a consonant stem. However, this rule is not valid for two-syllable verbs (⾒る mi-ru, for example, has a vowel stem) and verbs written only in hiragana (for example, びびる bibiru "to be surprised" and のめる nomeru "to fall forward" have consonant stems). Some consonant-stem verbs also have the syllable with the ending vowel written in hiragana, e.g. 混じる ma-jiru "to mingle" and the mentioned-above verb 抓める tsu-meru.
Examples of conjugation
The two "homophone verbs" ikiru and shimeru: