Not yet: chưa

Chưa before a verb means "not yet": Tôi chưa ăn. I haven't eaten yet. It says something hasn't happened so far, but still could. Không is a plain no: Tôi không ăn means I'm not eating, or I don't eat it.

Chưa is the no-answer to every "yet" question. When someone asks Em ăn cơm chưa? (Have you eaten?), say Rồi for yes and Chưa for no, never Không. A polite answer to someone older starts with dạ: Dạ, chưa.

For something you haven't done so far, use chưa, not đã không: Tôi chưa đi Đà Lạt. I haven't been to Đà Lạt yet. Chưa bao giờ means "never, up to now": Tôi chưa bao giờ ăn sầu riêng. I've never had durian.

Chưa works before adjectives too: Em chưa đói. I'm not hungry yet. Add vẫn for "still not": Em vẫn chưa hiểu. I still don't understand. And chưa có gia đình is how people say they're not married yet. At the end of an exclamation, chưa means "see?": Thấy chưa! See? I told you.