Learn Hardcore Chinese: nǐ kěyǐ zài shuō yíxià ma?

再 asks for a repetition in the future: “again/one more time” from now. It’s used for requests and planned repetitions.
又 describes something that has happened again (often in the past) or recurs habitually.
In a request like this, you want a repeat to happen now/next, so use 再: 再说…
Contrast:
- 他昨天又说了一遍。 “He said it again (yesterday).”
- 你可以再说一遍吗？ “Could you say it again (now)?”

What does 一下 after 说 do? Is it necessary?

一下 literally “one time/for a moment,” but after a verb it softens the request and implies a brief, light action.
Without 一下, 再说 can sound a bit more direct.
So 再说一下 ≈ “say it again (just briefly),” which is polite and gentle.
It’s optional: 你可以再说吗？ is grammatical but less soft.

How is 一遍/一次 different from 一下 here?

一遍 counts a full repetition from start to finish. Good when you want the entire sentence repeated clearly.
一次 counts occurrences (once, twice) without emphasizing completeness. In practice here it’s similar to 一遍.
一下 softens rather than counts; it suggests a quick/light repeat.
Politeness and nuance:
- 再说一下 = soft request
- 再说一遍/一次 = neutral, more about “repeat fully once”
- In class or when clarity matters, 再说一遍/一次 is common.

How polite is this sentence? How can I make it more or less polite?

As written, it’s polite and natural.
More polite:
- 您可以再说一遍吗？
- 请您再说一遍。
- 麻烦您再说一遍，好吗？
Less formal/casual:
- 再说一下，可以吗？
- 再说一遍吧。 (soft suggestion with 吧)
- Bare imperative (can sound brusque): 再说一遍。

Can I replace 你 with 您?

Yes. 您 is the polite “you” to show respect, e.g., to a teacher or elder:
- 您可以再说一下吗？

What’s the natural pronunciation with tone sandhi?

Under third-tone sandhi and the 一 tone rule, a natural reading is:
- ní kéyǐ zài shuō yíxià ma
Why:
- 你 nǐ (3) before 可 kě (3) → becomes 2nd tone: ní
- 可 kě (3) before 以 yǐ (3) → becomes 2nd tone: ké
- 再 zài (4) unchanged
- 说 shuō (1) unchanged
- 一 yī before a 4th tone (下 xià) → becomes 2nd tone: yí
- 下 xià (4) unchanged
- 吗 ma neutral tone

Why is 一 pronounced yí here?

Tone rules for 一:
- Before a 4th tone: yí (2nd tone) → e.g., yíxià
- Before 1st/2nd/3rd tone: yì (4th tone) → e.g., yìqǐ
- In isolation or when stressed as the number “one”: yī (1st tone)

Where does 再 go in the sentence?

再 comes before the verb it modifies:
- 你可以再说一下吗？
Don’t say: ❌ 你可以说再一下吗？
Other correct orders:
- 你再说一下，可以吗？
- 可以再说一下吗？ (subject omitted if context is clear)

Can I drop 你 or 可以?

Yes, if context makes the subject obvious:
- 可以再说一下吗？
Dropping 可以 turns it into a more direct imperative unless softened with 吗/吧:
- 你再说一下吧。 (softer)
- 你再说一下。 (more direct)

What’s the difference between 可以, 能, and 会 here?

可以: permission/politeness (“may/could”). Best for requests.
能: ability/possibility (“can”). Also fine in requests; a touch more about capability.
会: learned skill (“know how to”). Not appropriate for “repeat that” requests.
So: 可以/能再说一遍吗？ are both good; avoid 会再说一遍吗？ here.

Is 吗 required? How is it different from 呢 or 吧?

吗 makes it a yes–no question. Without it, the sentence is an imperative unless you add other softeners.
呢 doesn’t form yes–no questions by itself; it marks a topic or “how about…?”
吧 softens a suggestion/command: 再说一遍吧 = “Go ahead and say it again.”

Is 说 the only choice? What about 讲?

说 is the most common for “to say/speak.”
讲 is also used (more common in some regions), often with similar meaning:
- 你可以再讲一遍吗？
For “read aloud,” use 念/读:
- 你可以再念一遍吗？

How do I ask them to repeat more slowly or louder?

Add degree complements like 慢一点/慢一点儿, 大声一点, 清楚一点.
Word order options:
- After the verb phrase: 你可以再说一遍慢一点吗？
- Before the verb: 你可以再慢一点说一遍吗？
All are natural.

Is 一下儿 okay? What’s the difference?

Yes. In northern/Beijing-style speech you’ll hear 一下儿 (yíxiàr) with -r sound (儿化). Meaning is the same; it can sound even more casual.

Does 再说 have other meanings I should beware of?

Yes. 再说 by itself can mean:
- “We’ll talk about it later/let’s put it off” (e.g., 这个问题再说).
- “Besides/what’s more” as a connective.
In your sentence 再说一下, 再 clearly modifies 说 to mean “say again,” so there’s no ambiguity.

What are typical replies to this question?

Can I use the A-not-A pattern?

Are the spaces between words standard in Chinese writing?

No. Standard Chinese doesn’t use spaces between words. You’d write:
- 你可以再说一下吗？

Will 再说一下 sound too casual compared to 再说一遍?

再说一下 is polite and soft; it doesn’t sound rude or overly casual.
再说一遍/一次 is a bit more explicit about “one full repeat,” which can be clearer in noisy or classroom settings.