# Japanese godan and ichidan verbs

The Japanese language has two main types of verbs which are referred to as quinquegrade verbs (五段動詞, godan-dōshi) and monograde verbs (一段動詞, ichidan-dōshi).

## Terminology

Categories are important when conjugating Japanese verbs, since conjugation patterns vary according to the verb's category. For example, 切る (kiru) and 見る (miru) belong to different verb categories (quinquegrade and monograde, respectively) and therefore follow different conjugation patterns. Most Japanese verbs are allocated into two categories:
* Quinquegrade, quinquigrade, quinquagrade or pentagrade verbs (五段動詞, godan-dōshi)
* Unigrade or monograde verbs (一段動詞, ichidan-dōshi)
Statistically, there are about twice as many quinquegrade verbs than monograde verbs.
Classical Japanese had more verb groups, such as bigrade verbs (二段動詞, nidan-dōshi) and quadrigrade verbs (四段動詞, yodan-dōshi), which are archaic in Modern Japanese.
The word grade in quinquegrade and monograde is translated from dan (段). In grammar, dan is a synonym for retsu (列) and opposite to gyō (行). The translations for dan/retsu and gyō vary, either of them can be translated as "row" or "column", but the distinction is simply that gyō is named after consonants, as ka-row (か行, ka-gyō), while dan/retsu is named after vowels, as in i-column (い烈, i-retsu) or i-grade (い段, i-dan). The a-row (あ行, a-gyō) consists the kana a (あ), i (い), u (う), e (え), o (お), which differ only by vowels; while the a-grade (あ段, a-dan) consists of the kana a (あ), ka (か), ga (が), sa (さ), za (ざ), ta (た), da (だ), na (な), ha (は), ba (ば), pa (ぱ), ma (ま), ya (や), ra (ら), wa (わ), which differ only by consonants.
The quinquegrade (五段, godan) class consists of verbs whose inflection forms make use of all five grades, or five vowels. For example, the inflection forms of the verb kaku (書く, "to write; to draw", ka-row) are kaka (書か)/kako (書こ), kaki (書き), kaku (書く), and kake (書け). These verbs developed from the earlier quadrigrade (四段, yodan) class, after a historical sound change that turned such form as kakamu (書かむ) into kakō (書こう) and resulted in an additional vowel (see Late Middle Japanese).
The monograde (一段, ichidan) class consists of verbs that occupy only one grade, or one vowel. Dictionaries may further divide this class into "upper monograde" (上一段, kamiichidan)) if the vowel is the "upper" i, and "lower monograde" (下一段, shimoichidan)) if the vowel is the "lower" e. The verb miru (見る, "to look", ma-row), whose inflection forms are mi (見), miru (見る), mire (見れ) and miro (見ろ)/miyo (見よ), is an example of an "upper monograde" verb, and the verb eru (得る, "to earn", a-row) is a "lower monograde" verb. Some monograde verbs evolved from earlier forms of bigrade verbs (upper bigrade (上二段, kaminidan) and lower bigrade (下二段, shimonidan)).
Dictionaries often list ancestral forms of modern verbs as well as their classes. Thus, the entry for kaku may include a note like （動カ五［四］）, which means "verb, ka-row, quinquegrade, formerly quadrigrade"); while the entry for ukeru (受ける, "to take") may include （動カ下一）[文]カ下二 う・く, which means "verb, ka-row, lower monograde, lower bigrade equivalent in Classical Japanese is uku (受く)".
Note that the choices of prefixes in these English terms by some authors are rather inconsistent: while mono- is Greek, uni-, bi-, quadri- and quinque- are Latin (see Numeral prefix § Table of number prefixes in English). The word grade is actually Latin, not Greek in origin. While many authors use bigrade and quadrigrade consistently, they also use any combination of monograde, unigrade, quinquegrade, quinquigrade and pentagrade. Some dispense with quinquegrade (五段, godan) altogether and prefer only quadrigrade (四段, yodan) even for modern Japanese (see Godan vs yodan below). Plain English alternatives to "unigrade", "bigrade", "quadrigrade" and "quinquegrade" include "one-grade", "two-grade", "four-grade" and "five-grade"; "one row", "two row" and "four row"; "one-step", "two-step", "four-step" and "five-step"; or "one-vowel", "two-vowel" and "four-vowel".
Some Western analyses refer to "quinquegrade" verbs as "consonant-stem" verbs. Such analyses may represent the root form of the verb 書く as kak-, emphasizing the unchanging consonant k. "Monograde" verbs are then referred to as "vowel-stem" verbs.
Here is a visualization that compares various verb conjugations to an extracted column of the gojūon table:
| Quinquegrade Form | Quinquegrade Form | Quinquegrade Verb 読む (to read) | Gojūon table 'ma' column | Monograde Form | Monograde Form | Monograde Form | Monograde Form | Monograde Form | |
| Quinquegrade Form | Quinquegrade Form | Quinquegrade Verb 読む (to read) | Gojūon table 'ma' column | Negative | Polite | Dictionary | Potential | Volitional | |
| | Negative | 読まない yomanai | ま (ma) | | | | | | |
| | Polite | 読みます yomimasu | み (mi) | みない minai | みます mimasu | みる miru | みられる mirareru | みよう miyō | Upper Monograde Verb 見る (to see) |
| | Dictionary (no conjugation) | 読む yomu | む (mu) | | | | | | |
| | Potential | 読める yomeru | め (me) | 止めない tomenai | 止めます tomemasu | 止める tomeru | 止められる tomerareru | 止めよう tomeyō | Lower Monograde Verb 止める (to stop) |
| | Volitional | 読もう yomō | も (mo) | | | | | | |
In the table above, the verb 読む (yomu, to read) uses kana from all 5 rows of the gojūon table in its inflectional suffix—ま (ma), み (mi), む (mu), め (me) and も (mo)—amongst its conjugations. Thus, it is classified as a "class-5" (or more formally "quinquegrade") verb. Meanwhile, the verbs 見る (to see) and 止める (to stop) each use kana from only 1 row of the gojūon table in their verb-stem's suffix—み (mi) and め (me) respectively. Thus, they are classified as a "class-1" (or more formally "monograde") verbs. (See also Japanese verb conjugations.)

### Godan vs yodan

All modern godan verbs are derived from historical yodan verbs. The distinction between these two classes relies solely on the interaction between the mizenkei (未然形) and the "tentative" (推量, suiryō) auxiliary u (う) (historically, mu (む)). Consider the verb kaku (書く, "to write"):
* kaka- + -mu → kakamu (historical form) → kakau (historical form) → kakō (modern form)
The shift of vowels from au to ō was regular and expansive during Late Middle Japanese, and it practically introduced an additional dan (段, in other words, vowel) to the inflectional forms of yodan verbs:
Inflection of kaku (書く, "to write") :
| yodan (四段) | mizenkei (未然形) | ren'yōkei (連用形) | shūshikei (終止形) | rentaikei (連体形) | izenkei (已然形) | meireikei (命令形) |
| yodan (四段) | kaka- | kaki | kaku | kaku | kake | kake |
| godan (五段) | mizenkei (未然形) | ren'yōkei (連用形) | shūshikei (終止形) | rentaikei (連体形) | kateikei (仮定形) | meireikei (命令形) |
| godan (五段) | kaka- → kako-(u) | kaki | kaku | kaku | kake | kake |
The term godan (五段) is a fairly modern coinage. During the time when modern kana usage was being adopted to write modern Japanese (口語, kōgo, lit. 'spoken language') in place of historical kana usage, one of the changes concerned how such a form as kakō should be spelt. The modern spelling かこう was proposed along with godan as the name for the modernized yodan class. Traditionalist grammarians, on the other hand, would insist on such spelling as かかう to reflect the historical pronunciation kakau, and on the modern pronunciation being inferred from such spelling. Some argued that a single interaction with the auxiliary u did not justify creating an entire new grammatical class, given that the mizenkei does not involve a vowel shift with any other auxiliary:
* kaka- + -nai → kakanai
* kaka- + -nu → kakanu
* kaka- + -n → kakan
* kaka- + -zu → kakazu
Moreover, the auxiliary -ta and the particle -te also notably alter the ren'yōkei:
* kaki + -ta/-te → kaita/te
* omoi + -ta/-te → omotta/te
* yomi + -ta/-te → yonda/de
Yet, such alterations are not reflected by either the term yodan or the term godan at all, despite occurring in both these supposedly different inflections (although in classical Japanese (文語, bungo, lit. 'written language'), these alterations in pronunciation must be inferred from the spellings). This means that exceptional interactions with auxiliaries and particles like these ought not to be the basis for naming verb classes.
Obviously, the spelling reform took place and the term godan became mainstream. Historical kana usage is now reserved only for the writing of classical Japanese, and yodan verbs are largely considered a classical Japanese class while godan verbs make up a fundamental part of modern Japanese.

### Japanese language education

Within Japanese language education, various terminologies are used in lieu of the Japanese nomenclature for "quinquegrade" and "monograde" verbs.
| | Quinquegrade verbs | Monograde verbs | Irregular verbs | Example literature |
| Common terminology | Group 1 | Group 2 | Group 3 | A Dictionary of Basic Japanese Grammar |
| Common terminology | Group I | Group II | Group III | A Dictionary of Basic Japanese Grammar |
| Uncommon terminology | う-verbs (u-verbs) | る-verbs (ru-verbs) | Irregular verbs | GENKI |
| Rare terminology | Consonant stem verbals | Vowel stem verbals | - | Japanese: The Spoken Language |
In literature adopting the "Group I / II / III" terminology, the terms (I), (II) or (III) may be notated beside verbs. Similarly, (う) or (る) may be notated beside verbs in literature adopting the "う-verbs / る-verbs" terminology.

#### Consonant and vowel nomenclature

The terms "consonant stem verbs" and "vowel stem verbs" come from a pattern that emerges from studying the actual structure of the words rather than the written representation. When considering the invariant part of the verb (the verb stem), the final phoneme determines the classification of the verb group. If the verb stem's final phoneme:
* is a consonant, then it is a consonant stem verb (quinquegrade verb)
* is a vowel, then it is a vowel stem verb (monograde verb)
| | 読む (to read) | 走る (to run) | 見る (to see) | 食べる (to eat) |
| Negative | yom.anai 読まない | hashir.anai 走らない | mi.nai 見ない | tabe.nai 食べない |
| Polite form | yom.imasu 読みます | hashir.imasu 走ります | mi.masu 見ます | tabe.masu 食べます |
| Plain form | yom.u 読む | hashir.u 走る | mi.ru 見る | tabe.ru 食べる |
| Potential form | yom.eru 読める | hashir.eru 走れる | mi.rareru 見られる | tabe.rareru 食べられる |
| Volitional form | yom.ou 読もう | hashir.ou 走ろう | mi.you 見よう | tabe.you 食べよう |
| Invariant rōmaji | yom | hashir | mi | tabe |
| Final letter | m → consonant | r → consonant | i → vowel | e → vowel |
| Classification | Consonant stem | Consonant stem | Vowel stem | Vowel stem |
There are criticisms of the consonant and vowel nomenclature:
* When quinquegrade verbs end with "う" (u), the verb's invariant stem always ends with a vowel, yet is still classified as having a consonant stem. For example, 買う (kau, to buy) has the vowel "a" as the invariant suffix, yet it is still categorized as a "consonant stem verb". In these cases, this apparent expection is resolved by realizing that the verb's invariant stem ends in the consonant w. The w is normally suppressed, but surfaces in the negative form, as seen in 買わない (kawanai, to not buy). Traditionally these verbs ended in -hu, which is still seen on occasion in historical kana usage, and thus unambiguously ended in h.
* When godan verbs end with "つ" (tsu), the verb's invariant stem always ends with an "s" rather than a "t". Since the consonant stem terminology focuses on rōmaji, this could lead to conjugation errors. For example, 待つ (matsu, to wait) in its negative conjugation does not become "待つぁない" (matsanai) as the consonant stem system might have one believe; the correct conjugation is 待たない (matanai, to not wait). The matter is resolved when phonemic notation of "tu" used by Kunrei-shiki romanization is applied instead.
* In the case of the past-tense and te forms of conjugation, the 'invariant' stem changes such that the consonant is removed from all godan verbs (except verbs ending in "つ" (tsu) or "す" (su)). This means the defining characteristic of consonant stem verbs cannot be used to define consonant stem verbs for the past-tense or te forms. The true "invariant stem", which is consistent amongst all conjugations, precedes the so-called "invariant consonant".

## Verb classification

Classifying verbs is simple in theory:
* Take the verb in its plain, negative form. The result will be: verb-stem + ない (nai)
* If the last character of the verb-stem (ignoring the "ない"):
      * rhymes with 〜ぁ (-a), then it is a quinquegrade verb
      * rhymes with 〜ぃ (-i) or 〜ぇ (-e), then it is a monograde verb
| Negative verb | Last character of verb stem | Rhymes with | Group |
| 思わない (omowanai, to not think) | わ (wa) | 〜ぁ (-a) → | Quinquegrade verb |
| 行かない (ikanai, to not go) | か (ka) | 〜ぁ (-a) → | Quinquegrade verb |
| 起きない (okinai, to not wake up) | き (ki) | 〜ぃ (-i) → | Monograde verb |
| 食べない (tabenai, to not eat) | べ (be) | 〜ぇ (-e) → | Monograde verb |
This classification system works for all Japanese verbs, with three exceptions: ある (aru) is a quinquegrade verb, and both しない (shinai) and こない (konai) are instead classified as irregular verbs.

### Dot notation

In some Japanese dictionaries, the readings of conjugable words may have the stem and the inflectional suffix separated by a dot (・). For example, the adjective 赤い (akai, red) may be written as あか・い (aka·i) to separate the static prefix from the dynamic suffix.
This system also describes the verb group classification: in quinquegrade verbs, the dot is placed before the last kana; in monograde verbs, the dot is placed before the last 2 kana (except for 2-kana monograde verbs, which have no dot).
| | 3-kana verbs | 2-kana verbs |
| Quinquegrade verbs | かえ・る (kae·ru, to return) | い・る (i·ru, to need) |
| Monograde verbs | か・える (ka·eru, to change) | いる (iru, to exist) |
However, regardless of the dot's position, the inflectional suffix is always the last kana of any monograde verb.

### Naive verb classification

A caveat of accurately classifying verb groups is that you must have pre-existing knowledge of the verb's negative form. In practice, people tend to learn the verb's plain form first. As such, Japanese language educators usually teach strategies for naive verb classification. Whilst such strategies are not comprehensive, they generally remain useful in the context of regular daily conversations that language beginners will likely encounter. Here is one such strategy:
| Step | Verb (Plain Form) | If Yes | If Not |
| 1 | Is the verb one of the most common "exceptions": 要る (iru, to need), 入る (hairu, to enter), 走る (hashiru, to run), 帰る (kaeru, to return, to go home), 切る (kiru, to cut), 知る (shiru, to know), 喋る (shaberu, to talk) | Quinquegrade verb Group 1 | Go to Step 2 |
| 2 | Does the verb suffix rhyme with 〜ぃる (-iru) or 〜ぇる (-eru)? | Monograde verb Group 2 | Go to Step 3 |
| 3 | Is the verb する (suru, to do) or 来る (kuru, to come)? | Irregular verb Group 3 | Quinquegrade verb Group 1 |
Naive strategies, such as this one, tend to misidentify quinquegrade verbs ending with る (ru)—specifically, when quinquegrade verbs rhyme with 〜ぃる (-iru) or 〜ぇる (-eru). Therefore, when a monograde verb is concluded from a naive strategy, it is more efficient to confirm the verb's classification in a dictionary. However, there are other rules-of-thumb to more accurately discriminate such verbs.

#### Rules of thumb

If a dictionary is unavailable, it becomes difficult to discriminate quinquegrade verbs from monograde verbs when they rhyme with 〜ぃる (-iru) or 〜ぇる (-eru). The following heuristics aim to improve the accuracy of naive classification:
* There are far more quinquegrade verbs than monograde verbs.
* Verbs that do not rhyme with 〜ぃる (-iru) or 〜ぇる (-eru) are quinquegrade verbs.
    This includes verbs that rhyme with 〜ぁる (-aru), 〜ぅる (-uru) and 〜ぉる (-oru), which are quinquegrade verbs.
* The majority of verbs that rhyme with 〜ぃる (-iru) are quinquegrade verbs.
    248 of the 419 〜ぃる (-iru) verbs [ca. 60%] listed in JMdict are quinquegrade verbs.
* The majority of verbs that rhyme with 〜ぇる (-eru) are monograde verbs.
    2886 of the 3013 〜ぇる (-eru) verbs [ca. 95%] listed in JMdict are monograde verbs.
Kana and kanji based heuristics for 〜ぃる (-iru) and 〜ぇる (-eru) verbs:
* Verbs written entirely in hiragana are quinquegrade verbs. For example, びびる (bibiru, to be surprised) and のめる (nomeru, to fall forward) are quinquegrade verbs.
* Kanji verbs with 1 okurigana and 3+ syllables are quinquegrade verbs. For example, 契る (chi-gi-ru, to pledge) and 嘲る (a-za-ke-ru, to ridicule) are quinquegrade verbs.
* Kanji verbs with 2 okurigana are usually monograde verbs. For example, 起きる (okiru, to get up) and 食べる (taberu, to eat) are monograde verbs.
* Kanji verbs with 2 syllables are inconclusive. For example, 切る (ki-ru) and 見る (mi-ru) are both 2-syllable verbs, yet belong to different categories (quinquegrade and monograde, respectively)

## Quinquegrade verbs resembling monograde verbs

There are many quinquegrade verbs which may be mistaken for being monograde verbs in some cases (see § Naive verb classification, above). On the surface, this may seem like a problem that only affects conjugation patterns, since quinquegrade verbs and monograde verbs conjugate differently (See main article: Japanese verb conjugations). However there are many verbs that, despite having the same spelling, have different meanings and belong to different verb groups. For example:
| Quinquegrade verbs | Transcription (Rōmaji) | Monograde verbs |
| 要る (to need) | iru | 居る (to exist) |
| 切る (to cut) | kiru | 着る (to put on clothing) |
| 帰る (to go home) | kaeru | 変える (to change) |
| 湿る (to be damp/wet) | shimeru | 閉める (to close) |
When reading verbs such as these, the correct word meaning can be ascertained through the different kanji or accentuation. (See also Japanese pitch accent.) However, ambiguity is usually removed if the verbs have been conjugated somehow, because different word groups conjugate with slightly varying pronunciations. For example:
| Verb conjugation | kiru | kiru | kaeru | kaeru |
| Verb conjugation | Quinquegrade verb 切る (to cut) | Monograde verb 着る (to put on clothing) | Quinquegrade verb 帰る (to go home) | Monograde verb 変える (to change) |
| Negative | 切らない kiranai | 着ない kinai | 帰らない kaeranai | 変えない kaenai |
| Polite form | 切ります kirimasu | 着ます kimasu | 帰ります kaerimasu | 変えます kaemasu |
| Potential form | 切れる kireru | 着られる kirareru | 帰れる kaereru | 変えられる kaerareru |
| Volitional form | 切ろう kirō | 着よう kiyō | 帰ろう kaerō | 変えよう kaeyō |
Since there are so many quinquegrade verbs that resemble monograde verbs, it is impractical to create or memorize an exhaustive list of words.