Is there a particular reason why verbs are classified as "class 1" verbs (一段動詞) and "class 5" verbs (五段動詞)? Where did class 2 to 4 go? Do or did they exist at all, and why (not)?


  • 1
    I think you're assuming that "class 5" means that it's the fifth class, whereas I suspect that "class 5" really means that it has five classes.
    – Golden Cuy
    Commented Sep 7, 2014 at 0:36
  • 4
    But 段 doesn't mean "class". It means "grade" or "step".
    – Zhen Lin
    Commented Sep 7, 2014 at 0:37
  • 1
    More specifically, 段 here refers to the vowel column in the sounds chart. For example, き came be described as か行(ぎょう)い段(だん), and れ is ら行え段.
    – Dono
    Commented Sep 7, 2014 at 22:44

2 Answers 2


Before considering modern Japanese, I think that it is easier to understand this by first understanding classical. Classical Japanese has three major regular verb classes: quadrigrade (四段), monograde (一段), and bigrade (二段). Both monograde and bigrade may further be sub-divided into upper (上) and lower (下). There are also four irregular classes: k-irregular, s-irregular, n-irregular, and r-irregular. Verbs are conjugated into six forms: irrealis (未然形), adverbial (連用形), conclusive (終止形), attributive (連体形), realis (已然形), and imperative (命令形).

Let's consider the quadrigrade verb kak- 'to write' (書く). When conjugated to each of the above forms, it becomes kak-a, kak-i, kak-u, kak-u, kak-e, kak-e. Notice that the distinctive suffixes are a, i, u, e. The total number of distinctive suffixes is four, which is why this is called quadrigrade (四段).

Next, let's consider the monograde verb mi- 'to see' (見る). When conjugated to each of the above forms, it becomes m-i, m-i, m-iru, m-iru, m-ire, m-iro. Notice how all of the forms contain a single -i. This is why it is called monograde (一段). Now let's consider the verb tabe- 'to eat' (食べる). It conjugates as tab-e, tab-e, tab-eru, tab-eru, tab-ere, tab-ero. This time all of the forms contain a single -e. This too is monograde. To distinguish between these two, those ending in -i are called upper monograde and those ending in -e are called lower monograde. The normal vowel ordering in Japanese is a, i, u, e, o. Notice that comparing i and e, i comes first and e comes second. Traditionally these would be written vertically. As a result, i is considered to be "upper" and e is "lower" in this chart, hence the names.

Next let's consider the bigrade verb ok- 'to rise' (起く). (Older form of modern oki- 起きる 'id'.) When conjugated to each of the above forms, it becomes ok-i, ok-i, ok-u, ok-uru, ok-ure, ok-i[yo]. All forms have an -i or -u in it. This is a two-way distinction, hence the name bigrade. Now let's consider the (older) verb tab- 'to eat' (食ぶ). This conjugates as tab-e, tab-e, tab-u, tab-uru, tab-ure, tab-e[yo]. Again there is a two-way distinction, so this too is bigrade. However, this time the distinction is between -u and -e. As such, bigrade may be sub-classified into upper bigrade (i/u) and lower bigrade (u/e).

The four irregular verb classes are simply irregular which explains their names.

Now let's look at modern Japanese. Modern Japanese simplifies much of the above: all quadrigrade verbs have now become quintigrade (五段), bigrade verbs have gone bye-bye (pun intended), and two of the four irregular classes have disappeared. Also note that the conjugation class formerly known as realis (已然形) is now known as conditional (仮定形).

Let's consider the new quintigrade verb. In addition to the four distinctions earlier, there is now a fifth, hence the name. This fifth form is -o. This can be seen in kak-o: "(I) shall write, let's write". However, this form is secondary in nature: it derives from kak-au (and earlier kak-amu). -au- regularly changes into o: (long o). This -a is the same -a as seen in the irrelias (未然形). This is not a true form, but is added to by-pass the phonological explanation.


Ichidan verbs keep a single root when conjugated, hence their name. For example 見る is 一段 so it keeps its み- stem. みる みます みない みれば みよう みて みた are used for the infinitive, conjunctive, negative, imperative, volitional, connective and past forms, respectively.

On the other hand 五段 verbs change according to the verb form. For example 読む would be よむ よみます よまない よめば よもう よんで よんだ respectively. You can see that the final "mu" of "yomu" can change to mi, ma, me and mo (in addition to mu!), making it 5.

There aren't any 2, 3 or 4段 verbs in modern Japanese. Only two types of verbs, yay!

EDIT: I just realized you might be asking WHY it's this way... In which case I have no idea!

  • 1
    There used to be 二段 and 四段 though, and the question asks about these. Would you like to add anything to your answer?
    – user1478
    Commented Sep 6, 2014 at 21:10
  • Really no expert! I thought it was a basic grammar question ;P You'd be better writing a more appropriate yourself :) Never heard of 二段 or 四段 verbs!
    – comeauch
    Commented Sep 6, 2014 at 21:15
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    @snailboat I suspect that the OP is assuming that if there's 五段動詞, then logically there must have been not only 二段 and 四段, but also 三段, and I think that's a faulty assumption.
    – Golden Cuy
    Commented Sep 7, 2014 at 0:44
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    I do not see any reason to downvote this answer. The OP incorrectly assumed that 一段動詞 and 五段動詞 meant “class-1 verb” and “class-5 verb,” respectively, and that there must be class-2, class-3, and class-4 verbs before someone calls something class-5 verb. The entire assumption is faulty, and this answer explains exactly why. The fact that there were 二段動詞 and 四段動詞 in the past is a red herring, and does not resolve the OP’s original confusion. Commented Sep 7, 2014 at 1:38
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    As background for native Japanese speakers reading this, most non-Japanese hear the term "dan" in English, if at all, in the context of various martial arts such as akido. You'd start off as first dan, then progress to second dan, etc. until you reach fifth dan.
    – Golden Cuy
    Commented Dec 5, 2014 at 12:32

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