Identifying ichidan and godan verbs from polite (masu) form?

Question

I've googled, and it only comes up with results for the plain form of verbs. Is the answer just to change the polite form to plain form and then distinguish? If so, how do I do that?

Answer 1

Excluding the two irregular (Group-3) verbs (i.e. します and [来]{き}ます), a verb is an ichidan (Group-2) verb if it satisfies either of the following conditions.

1. The syllable immediately before ます is of the /e/ sound (e.g. あげます, [食]{た}べます, [出]{で}ます)
2. It has only one syllable before ます (e.g. います, [見]{み}ます, [着]{き}ます)

As a rule, all other verbs are godan (Group-1) verbs.

However, there are exceptions such as [起]{お}きます, [降]{お}ります and [借]{か}ります, which are ichidan (Group-2) verbs despite having multiple syllables before ます and the final one is of the /i/ sound. You should memorize them as exceptions.

[Note] If the syllable immediately before ます is not of the /e/ sound, it is always of the /i/ sound.