How to deduce the verb class in Japanese language

How to distinguish between ichidan (ru-verb) and godan (u-verb).

Here's a simple rule: if a verb’s dictionary form does not end in eru or iru, it is definitely an u verb. If it ends in eru or iru, it can be either a ru verb or an u verb.
Examples of u-verbs (godan) :

• 書く kaku (write) 
• 読む yomu (read) 
• 売る uru (sell) 
• とる toru (take) 
• なる naru (become) 

It is helpful to know that most eru/iru-ending verbs are ru verbs. So, you can just memorize

a handful of frequently used eru/iru-ending u verbs, such as the following:

U verbs that end with eru:

• 帰る kaeru (return)
• しゃべる shaberu (chat)
• 減る heru (decrease)
• 蹴る keru (kick)
• 滑る suberu (slide)
• 練る neru (knead)
• 照る teru (shine)

U verbs that end with iru:

• いる iru (need)
• 入る hairu (enter)
• 知る shiru (get to know)
• 切る kiru (cut)
• 走る hashiru (run)
• 参る mairu (go, honorific)
• 煎る iru (roast)
• 散る chiru (scatter)
• 混じる majiru (mix)
• 限る kagiru (limit)
• ねじる nejiru (twist)

It is also helpful to know that you can deduce the verb class if you compare the most frequently used two forms—the dictionary form and the masu form. Just remove る ru and ます masu. If what remains is exactly the same, you can conclude that it is a ru verb. Otherwise, it is an u verb. See the following example:

	Dictionary Form	masu Form
Ru verb	きる (wear)	きます
U verb	きる (cut)	きります

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Reference:

Sato, E., 2014. Complete Japanese Grammar. New York: McGraw-Hill, pp.36-38.