It is incredibly easy to turn a statement into a question in Japanese—all you need to do is add the particle か to the verb.
|山田さん は 先生 です。
|Yamada-san is a teacher.
|山田さん は 先生 ですか？
|Is Yamada-san a teacher?
|マイク は 水 を 飲みます。
|Mike will drink water.
|マイク は 水 を 飲みますか？
|Will Mike drink water?
In formal writing, there is no need for the question mark (it never used to exist in Japanese) as か makes it clear that the sentence is a question; however, in most non-literary texts it will be in included.
If we change the verb to the negative then we can use か to make a suggestion or an invitation.
|一緒 に 食事 を しませんか？
|Won’t you have dinner together?
|飲み会 に 来ませんか？
|Won’t you come to the drinks?
We can also add か to the standard form of the verb (this structure has a key grammatical function, as we shall see later); however, this is rarely a structure used to ask a question—it is too blunt. Instead, you will see の or なの added, depending on the sentence ending.
- の is used if the sentence ends in a verb or i-adjective
- なの is used if the sentence ends in a na-adjective or noun
|Are you busy now?
|その ビル は 学校なの？
|Is that building a hospital school?
In casual conversation you can also put make the question in statement form and let a change in intonation do the rest, e.g. “You going?”
|Will you eat?
|ジョン は 会計士？
|Is John an accountant?
Note that you will never hear this way of questioning used with the copula—either standard or polite.
ジョン は 会計士 だ？ (✘)
ジョン は 会計士 です？ (✘)