Japanese consonant and vowel verbs

The Japanese language has two types of regular verbs that involve the stem, and can be referred to as Japanese consonant and vowel verbs.

Verb groups

The two groups of verbs are:

consonant-stem,, Group I, or -u verbs; and
vowel-stem,, Group II, or -ru verbs.

Most verbs are consonant-stem, but vowel-stem verbs are also common, hence the numbering "Group I" and "Group II". Sometimes categorization is expanded to include "Group III" 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, -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 are based on the number of vowel suffixes used to form verb roots for conjugations. Classical Japanese had more verb groups 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 見れる mireru and 食べれる 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 have also irregular potential forms are ik.eru/ik.areru and kik.eru/kik.oeru. Other irregular potential forms are suru→dekiru and kuru→korareru.

Consonant-stem verbs ending in -u may not appear to conjugate "after a consonant"; for example, the polite form of kau is kaimasu. 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. 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 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 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:

読まよま yoma- as in yomanai,
読みよみ yomi- as in yomimasu,
読むよむ yomu- as in yomu,
読めよめ yome- as in yomeba,
読もよも yomo- as in yomō .

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:

見み mi-

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:

食べたべ tabe-

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:

帰るかえ・る kae.ru "return" – consonant stem ラ行五段
変えるか・える ka.eru "change" – vowel stem ア行下一段

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:

要るい・る i.ru "need" – consonant stem ラ行五段
居るいる iru "be " – vowel stem ア行上一段

The terms "Group I", "Group II", and "Group III" are primarily used in Japanese language education, and may be notated as,, next to a verb. Similarly, the terms "u verb" and "ru verb" are educational terms, and may be notated as （う） or （る）.

Verbs ending in ''-iru'' and ''-eru''

General

Vowel-stem verbs, such as 見る miru "to see" and 食べる taberu "to eat," end either in -iru or -eru, but some consonant-stem verbs have these endings, too, and there are also "homophone verbs" that have either a vowel stem or a consonant stem.

Rules of thumb

There are more consonant verbs than vowel verbs.
All verbs not ending in -iru/-eru are consonant-stem verbs; this includes -aru/-uru/-oru verbs and verbs with a vowel ending in the basic form, such as 買う kau "to buy" and 言う iu "to say."
Over half of verbs ending in -iru have a consonant stem, and the majority of verbs ending in -eru has a vowel stem.
If the vowel i/e of the ending -iru/-eru is part of a kanji, as opposed to being part of an okurigana, chances are high that the verb has a consonant stem.
* However, this rule is not applicable for two-syllable verbs and verbs written only in hiragana. 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 "to pinch."
* -eru verbs having the e sound written in hiragana listed in EDICT: 2934
* -eru verbs having the e sound in a kanji listed in EDICT: 139.
Examples of conjugation

The "homophone verbs" iru and eru :

	Vowel stem	Consonant stem	Vowel stem	Consonant stem
Plain form
Negative
Polite form
Potential form ¹
Volitional form

¹ Potential forms of consonant verbs are conjugated like vowel verbs: ireru / ereru → iremasu / eremasu, etc. The same is true for passive forms. In vowel verbs, potential and passive forms are identical.
Rule of thumb: In vowel verbs, the basic-ending -ru is completely replaced by the new ending, while in consonant verbs, the -r sound is kept and followed by another vowel, to which the new ending is added. However, in the -te/-ta forms, consonant verbs drop the -r sound and replace it by -tte/-tta, while vowel verbs have -te/-ta.

Lists of verbs (examples)

The following lists are not complete; feel free to add other verbs.

Homophone vowel-stem and consonant-stem verbs ending in ''-iru''

Verb	Vowel stem	Consonant stem
chibiru
hiru
ikiru
iru
kiru
komiiru

Homophone vowel-stem and consonant-stem verbs ending in ''-eru''

Verb	Vowel stem	Consonant stem
eru
fukeru
furikaeru
fuseru
heru
hineru
kaeru
kakeru
mochikaeru
mikaeru
nameru
neru
okikaeru
shimeru
suberu
takeru

Consonant-stem verbs ending in ''-iru''

Note: Homophone verbs listed above are not repeated here.

Verb	Kanji and/or hiragana	English
aburagiru	脂ぎる	to be greasy
bibiru	びびる	to be surprised
chigiru	契る	to pledge
chiru	散る	to scatter
dojiru	どじる	to mess up
guchiru	愚痴る	to grumble
hairu	入る	to enter
hashiru	走る	to run
hojiru	穿る	to pick, dig out
hotobashiru	迸る	to gush, spurt
ibiru	いびる	to torment, roast
ijiru	弄る	to fiddle with
kagiru	限る	to limit
kajiru	齧る	to gnaw
kashiru	呪る	to curse
kishiru	きしる	to become misty
kishiru	軋る	to squeak, creak
kojiru	抉る	to gouge, wrench
kubiru	括る	to grip, strangle
kujiru	抉る	to gouge, scoop
mairu	参る	to come/go - humble
majiru	混じる	to mingle
meiru	滅入る	to feel depressed
mikubiru	見縊る	to belittle; to despise
minagiru	漲る	to overflow
mogiru	捥る	to wrench
mojiru	捩る	to parody, to twist
mushiru	毟る	to pluck, to pick, to tear
najiru	詰る	to rebuke
nejiru	捩じる	to twist
nigiru	握る	to grasp
nijiru	躙る	to edge forward
nonoshiru	罵る	to abuse verbally
ochiiru	陥る	to fall, sink
omoiiru	思い入る	to ponder, to contemplate
omoikiru	思い切る	to dare to or omoikitta
sebiru	せびる	to pester for
shiru	知る	to know
soshiru	謗る	to slander
sujiru	捩る	to wriggle
tagiru	滾る	to boil, to seethe
tamagiru	魂消る	to be frightened
tobashiru	迸る	to gush
tochiru	とちる	to muff lines
yajiru	弥次る・野次る	to jeer at
yogiru	過る	to pass by, to drop in
yojiru	捩る	to twist, distort
yokogiru	横切る	to traverse

Consonant-stem verbs ending in ''-eru''