terminology - What's the difference between Ichidan/Godan and Ru/U verbs classification?

I've come across two different ways (at least, apparently for me) to classify verbs. Please note that this question is fundamentally different from Verb classifications by japanese learners.

The first classification is to divide verbs into Godan and Ichidan, which I think is good for reference, but not clear at all for learners (you can't really guess the number of conjugations by just looking at the verb).

The second, which I personally find clearer, is to divide them into る- and う-verbs. According to this last division:

With the exception of two verbs, all verbs fall into る- or う-verbs.

All る-verbs end in る, while う-verbs end in -う (including る). Therefore, if a verb does not end in る, it'll be necessarily a う.verb.

For verbs ending in る, if the vowel preceding る is /a/, /u/, /o/, it will always be an う-verb. If the vowel is /e/ or /i/, it will be a る-verb in most cases.

So what's the difference between the two? Is one system adopted by Japanese and the other adopted by learners (e.g. in JLPT)? Or they totally coincide but just have different names?

Answer

Answer: They're not different. Not exactly, anyway. Each group ends up describing the same verbs; they just arrive at their classification by different routes.

• All う-verbs are 五段【ごだん】 verbs (and vice-versa).


• All る-verbs are 一段【いちだん】 verbs (and vice-versa).

う-verbs and る-verbs

I learned the う-/る- distinction as well (as likely most English-speakers did), though under the guise of "Class 1", "Class 2", and "Class 3" (the two irregulars). How I learned to classify them is by the past-tense form, however. For example:

Class 1

～う、～つ、～る ⇒ ～った
～ぬ、～む、～ぶ ⇒ ～んだ
～す ⇒ ～した
～く ⇒ ～いた
～ぐ ⇒ ～いだ

Class 2

～る ⇒ ～た

Class 3

する ⇒ した
くる ⇒ きた

There was even a catchy song to go along with it!

One advantage of this method is that it kills two birds with one stone: you learn verb classification at the same time as you learn the past-tense conjugation. It also avoids confusing or intimidating new learners by throwing big words at them.

五段【ごだん】 verbs and 一段【いちだん】 verbs

On the other hand, the 五段【ごだん】・一段【いちだん】 distinction, like you noted, is derived from the number of different forms in the base stem forms of Japanese grammar -- a concept which second-language learners of Japanese usually are not even taught.

One advantage of this distinction is that the names actually describe something deeper about how the verbs work. But isn't it hard to guess the number of conjugations by looking at the verb? Actually, not really. Any verb that matches your "う-verb" definition will have those five conjugations, always.

That's all the difference is.