What exactly are ア行-category verbs?


The question [Why are there so many カ行、サ行、ラ行五段活用
verbs?](https://japanese.stackexchange.com/questions/80848/why-are-there-so-
many-%e3%82%ab%e8%a1%8c-%e3%82%b5%e8%a1%8c-%e3%83%a9%e8%a1%8c%e4%ba%94%e6%ae%b5%e6%b4%bb%e7%94%a8-verbs)
is about different verb categories. I was surprised to find a ア行-category
mentioned, and when I checked on weblio, they seemed to have listed only four
verbs in this category, at least for 五段 (<https://www.weblio.jp/parts-of-
speech/%E3%82%A2%E8%A1%8C%E4%BA%94%E6%AE%B5%E6%B4%BB%E7%94%A8_1>). To top it
all of, they all end in 合う, which is by itself listed as ワ行, not ア行.

This all seems rather strange to me, so I would be grateful for an
explanation. Thanks for reading!




There are conjugation forms, and one of them is the five-stage conjugation.
There are pentadic conjugations, which are conjugated with each step of the
syllabic chart "a-i-u-e-o" at the end of a word. (The most common verb
conjugation is the five-step conjugation. The five conjugations are the
changes of the five conjugations: preemptive, continuous, terminating,
linking, hypothetical, and imperative.

Take the example of 「合う」 in the link.

  * The non sequential form (preceding the auxiliary verb "ない", "う", "れる", etc.) 
    * 「合わ(wa)ない」 The sound of "a" ...... ア段
    * 「合お(o)う」 The sound of "o" ......... オ段
  * Adjunctive form (preceding the auxiliary verbs "ます," "た," and "たい," etc.) Abortive forms (forms that are cut off by ","). The form preceding the auxiliary verb "て", "たり", "ながら", etc.) 
    * 「合い(i)ます」 The sound of "i" ............ イ段
  * Ending form (a form of saying off. The form preceding the auxiliary verb "まい" or "らしい". The form preceding the auxiliary verb "と," "から," "けれど," etc.) 
    * 「合う(u)」 The sound of "u" ............ ウ段
  * Adnominal form (preceding a noun or pronoun) 
    * 「合う(u)とき」 The sound of "u" ............ u-dan
  * Hypothetical form (preceding the particle "ば") 
    * 「合え(e)ば」 The sound of "e" ......... エ段
  * Imperative (the form of commanding and saying a sentence out loud) 
    * 「合え(e)」 The sound of "e" ............ エ段

It goes like this.

  * [未然形](https://www.weblio.jp/content/%E6%9C%AA%E7%84%B6%E5%BD%A2)
  * [連用形](https://www.weblio.jp/content/%E9%80%A3%E7%94%A8%E5%BD%A2)
  * [終止形](https://www.weblio.jp/content/%E7%B5%82%E6%AD%A2%E5%BD%A2)
  * [連体形](https://www.weblio.jp/content/%E9%80%A3%E4%BD%93%E5%BD%A2)
  * [仮定形](https://www.weblio.jp/content/%E4%BB%AE%E5%AE%9A%E5%BD%A2)
  * [命令形](https://www.weblio.jp/content/%E5%91%BD%E4%BB%A4%E5%BD%A2)

