Again: 又 vs 再

Both 又 and 再 translate to "again" in English, but they are not interchangeable. The key distinction is time reference: 又 looks backward at something that has already repeated, while 再 looks forward at something that will repeat.

又 describes repetition that already occurred: 他昨天又迟到了 — "He was late again yesterday." The lateness already happened (again). 又 often carries a tone of mild annoyance or emphasis: 你又忘了！ — "You forgot again!" It can also express "both...and": 又便宜又好吃 — "both cheap and delicious."

再 describes repetition that has not yet happened: 请再说一遍 — "Please say it again" (you haven't said it yet). 下次我再来 — "I'll come again next time." 再 is also used in polite requests and future plans. The sentence 再见 (goodbye) literally means "again see" — we will see each other again.

A helpful shortcut: if the action has already happened → 又. If the action hasn't happened yet or you're asking someone to do it → 再. When in doubt, check: did the repetition already take place?