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a. If the verb is a Group 2 Verb, simply remove the final “masu” syllable and replace it with “you:”

食べます → 食べよう (Tabemasu → Tabeyou)

b. If the verb is an Group 1, its final vowe" imasu" must be changed to “ou,” which means its final syllable must be replaced (for example, if the verb in question is “Yomimasu ” change it to “yomou”.

読みます → 読もう (Yomimasu  → Yomou)

c. If your verb ends with a syllable that is just a vowel (e.g. “Kaimasu,” to buy), the pattern is the same:

買います → 買おう (Kaimasu → Kaou)

d. The irregular verbs “Shimasu ” (to do) and “Kimasu ” (to come) conjugate thusly:

します → しよう (Shimasu → Shiyou)
来ます → 来よう (Kimasu → Koyou)

e. Plain Volitional Form can be used in the same way as Polite Volitional Form.
First, conjugate the verb in question into stem form. Then, add “-mashou” to the end of the stem. For example, the stem form of the verb “yomu” (to read) is “yomi;” so the Polite Volitional Form of “yomu” is “yomi mashou.”

読む → 読み → 読みましょう

お茶を買って、外で教科書を読みましょう。
Ocha o katte, soto de kyoukasho o yomi mashou
(Let’s buy tea, and read the textbook outside).

私達はカフェに行きましょう。
Watashi tachi wa kafe ni ikimashou
(Let’s us go to the café).
 
If you would like to make your suggestion into a question, simply add the question particle “ka” to the end of the sentence:

教科書を読みましょうか。
kyoukasho o yomi mashou ka
(Shall we read the textbook?)

If you were to translate both 教科書を読みましょう (kyoukasho wo yomi mashou) and 教科書を読もう (kyoukasho o yomou) to English, it would be hard to differentiate between the two sentences. Their essential meaning is identical.

The only real difference between “yomi mashou” and “yomou” is that the latter is much more casual, and should be used primarily with peers or with those younger than oneself. (This is as opposed to bosses, adults older than oneself, strangers, etc).

f. Just as with Polite Volitional Form, a “ka” question particle can be added onto the end of a Plain Volitional Form suggestion if you would like to turn the suggestion into a question.

教科書を読もうか。
kyoukasho o yomou ka
(Shall we read the textbook?)
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