かいQuestion marker

The sentence ending particle かい is a grammar structure that is used in Japanese to highlight a question. Despite commonly being thought of as one word, it is actually the combination of か (the sentence-ending particle) and い, another sentence-ending particle that is primarily used by men (in a similar way to ね and よ).

かい will usually be used directly after the word or phrase that it is highlighting. In the case of verbs and い-Adjectives, の may be inserted before かい. For な-Adjectives and nouns, なの may be inserted directly before it. However, の (or なの) are frequently omitted, due to how casual かい is.

When it is not omitted, の (or なの) may be shortened to ん (or なん）. This is in the same way that の and なの would behave in the のです and なのです grammar structures.

Although there are some exceptions, かい will almost always be used to ask simple yes/no questions.

Caution

Because かい is very casual, and quite direct, it often sounds like an accusation. Due to this, care should be taken with your tone of voice, so as not to be taken the wrong way.

Fun Fact

Outside of かい, the sentence ending particle い is not commonly used in modern Japanese, and therefore will only appear in a few very specific structures (like だい). Despite being similar to ね, い is considered to be fairly ぞんざい 'rough', and should only be used with people that you are very familiar with, and never to someone above you.