How to denote particular kana sounds in Japanese?

Question

In romaji, the ways that verbs inflect is fairly straightforward to indicate. For example, if you wanted to describe the process under which 五段動詞｛ごだんどうし｝ change from 辞書形｛じしょけい｝ to 可能形｛かのうけい｝. One could say something like the following.

Replace the "-u" with "-eru."

Example: 飲む｛のむ｝　→　飲める

Of course, this is assuming that we're aware of and abide by the linguistic rules of Japanese pronunciation, which means things like that if you have a "-tsu" ending and want to replace "-u" with "-eru", this really means to change "-tsu" to "-teru," not "-tseru."

If you wanted to make a note like this in Japanese, however, it's a little awkward.

「～う」というのを「～える」というのに変｛か｝えてください。

It's awkward because this rule really applies to the u/e sounds and not the う・え kana specifically. For instance, if you wanted to apply this rule to the verb 飲む, it might be unclear what it means to replace 「～う」 with something when the kana う is not present.

How, in Japanese, does one denote in a short note form something like the "Replace the -u with -eru." sentence I indicated above?

Answer 1

You can use 段【だん】 (literally "column") to refer to the vowel of a kana. For example, エ段のカタカナ refers to エ, ケ, テ, and so on. (As an aside, 行【ぎょう】 refers to "row", i.e., consonant. ダ行のカタカナ refers to ダ, ヂ, ヅ, デ and ド.)

With this, the idea of:

Replace the "-u" with "-eru."

can be conveyed like so:

• 最後の文字の母音をウ段からエ段に変えて「る」を付ける
• 活用語尾をエ段に変えてルを足す

Of course, native Japanese speakers usually don't need a sentence like this, and someone who can read a sentence like this can also read romaji, too. Japanese Wikipedia doesn't explain this conjugation rule :)