không / chưa

Both không and chưa are placed directly before the main verb or adjective they negate. To negate a noun, you must use không phải là (is not) or chưa phải là (is not yet) instead.

• Không (Not / No): Expresses outright, general negation. It denies a fact or state with no expectation of it happening later. For example, saying Tôi không ăn thịt (I don't eat meat) means you are a vegetarian.
• Chưa (Not yet): Expresses temporal unfulfillment. It means the action hasn't happened up to now, but it might happen later. Saying Tôi chưa ăn thịt (I haven't eaten meat yet) means you just haven't eaten it yet today, or haven't tried it before.

Forming Questions:
You can form yes-no questions using the framing structures có ... không? and đã ... chưa?. In casual speech, the words có and đã are frequently dropped, leaving just không or chưa at the end of the sentence (e.g., Bạn đói không? or Bạn ăn chưa?). Using không asks for a simple fact ('Do you...?'), while using chưa asks if an expected action is completed ('Have you yet?').

Answering Questions:
To answer a full có ... không? question, you can reply with có (yes) or không (no). However, a blunt có or không can sound abrupt. Native speakers often soften it by adding a polite particle like dạ (e.g., Dạ có / Dạ không), repeating the main verb, or using không ... đâu (not at all / absolutely not) to add emphasis or soften the bluntness. If the question drops có, native speakers naturally reply by repeating the main verb or adjective (e.g., Đói or Không đói). To answer a chưa question, reply with rồi (already) if the action is completed. If it isn't, you can say chưa, or use the highly common conversational replies vẫn chưa (still haven't) and chưa đâu (not yet!).

Past Tense Negation:
Because English uses 'did not' for the past tense, learners often try to say đã không. However, this sounds unnatural and like 'translationese' to native speakers in everyday speech, though you might still encounter it in formal writing, literature, or news broadcasts. Instead, casual spoken Vietnamese often just uses không + [time word] (e.g., Hôm qua tôi không đi - I didn't go yesterday). For stronger emphasis or clearer past negation, especially in Southern Vietnamese, use the structure không có + [verb] (e.g., Tôi không có đi - I didn't go). Be careful not to confuse this with không có + [noun], which literally means 'do not have' (e.g., Tôi không có tiền - I don't have money).

Note: In casual Southern speech, the 'kh' in không is often dropped, softening the word to hông.