## 又, 再 and 還

All three of these adverbs indicate the repetition of an action, like
the English "again". They differ in usage, however:

Whereas 又 indicates a repetition of an action that has already taken
place, 再 implies a repetition of an action in the future. Also, 再 is
only used in /declarative/ sentences, plus questions ending in 好嗎:

    昨天他來晚了﹐今天他又來晚了。
        (repetition in the past)
    你今天來晚了﹔明天再來晚﹐我們就不讓你進來了。
        (repetition in the future)
    你再喝一點兒橘子水﹐好嗎﹖

Also, 又 can be used for the repetition of a periodic action or
occurrence, even though it has not yet taken place:

    明天又是星期一﹐我們又要上課。
    新年又要來了。

還, on the other hand, usually expresses a future repetition:

    你明天還來嗎﹖

It can also be used in an interrogative or declarative sentence with an
optative verb. In this situation, it is placed before the optative verb
and an optional 再 can be placed after:

    A: 你明年還能(再)教我們嗎﹖
    B: 我明年還可以(再)教你們。