# Biết đâu: who knows, maybe in Vietnamese (B1)

> Biết đâu at the start of a sentence means "who knows, maybe": it raises a possibility nobody can rule out. Biết đâu ảnh lại đồng ý.

Source: https://vietnamesebuddy.com/grammar/biet-dau-maybe/ · Updated 2026-10-17

**who knows, maybe**

Pattern: `Biết đâu + [person or thing] + (lại) + [verb] · Biết đâu được!`

Level: B1 (our estimate) · Register: everyday

Typed without accents: biet dau

Saigon: biết đâu được | Hà Nội: biết đâu được; biết đâu đấy

Variants:

- biết làm sao được (what can you do)

*Biết đâu* at the start of a sentence means "who knows, maybe": it raises a possibility nobody can rule out. *Biết đâu ảnh lại đồng ý.* Who knows, he might say yes (in Hà Nội, *anh ấy*). *Lại* before the verb often goes with it, when the outcome would go against what you expect.

Very often it gives a reason to do something: try, ask, or be ready. The suggestion comes first and *biết đâu* follows: *Mua vé số đi, biết đâu trúng.* Buy a lottery ticket, you never know, you might win. *Mang dù theo đi, biết đâu trời mưa.* Take an umbrella, it might rain (in Hà Nội, *ô*).

As a reply on its own, say *Biết đâu được!* (in Hà Nội, also *Biết đâu đấy!*): you never know!

*Có lẽ* (perhaps) is a guess about what's probably true. *Biết đâu* keeps a chance open, often a hopeful one. *Sợ là* expects the outcome you don't want: *Em sợ là trời mưa.* I'm afraid it'll rain. And *liệu* simply asks: *Liệu trời có mưa không?* I wonder if it'll rain.

Watch the place. After a person, *biết đâu* means the opposite, "how would I know?": *Em biết đâu!* That's the same push-back as *Em đâu có biết!*: you're saying you had no idea, not raising a possibility.

## Examples

- Saigon: Biết đâu ảnh lại đồng ý. | Hà Nội: Biết đâu anh ấy lại đồng ý. — Who knows, he might say yes.
- Mua vé số đi, biết đâu trúng. — Buy a lottery ticket, you never know, you might win.
- Saigon: Mang dù theo đi, biết đâu trời mưa. | Hà Nội: Mang ô theo đi, biết đâu trời mưa. — Take an umbrella, it might rain.
- Cứ thử đi, biết đâu được. — Just give it a try, you never know.

## Compare

- [Perhaps: có lẽ](https://vietnamesebuddy.com/grammar/co-le-perhaps/): perhaps
- [But I didn't! có … đâu, đâu có](https://vietnamesebuddy.com/grammar/co-dau-denial/): denying what was said
- [I wonder whether: liệu … (có) … không?](https://vietnamesebuddy.com/grammar/lieu-wonder/): I wonder whether; will it really
- [I'm afraid that: sợ (là), e (là)](https://vietnamesebuddy.com/grammar/so-la-afraid/): I'm afraid (that), softening bad news

Previous in Can, must, should, want: [Should have: đáng lẽ (ra), lẽ ra](https://vietnamesebuddy.com/grammar/dang-le-should-have/)

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