Which iru and eru verbs are actually group I (consonant) verbs?
Here is some general advice on how to pick out these ones. If …eru and …iru words have more than one syllable before the -ru, and you can find out how they are written in kanji, whether or not the syllable ending with “e” or “i” is written in kana, or the -ru comes right after the character, will usually tell you. If the vowel is included in the kanji, it will be a consonant verb (-tte, -ranai, etc.). This doesn’t work for one-syllable roots such as “mi-ru,” of course. And usually, if you have what is needed to find out how it is written, you have the information you want in the same source.
