Polite yes dạ / vâng, casual yes ừ

Dạ is the polite way to say yes, or just to show you're listening, when you talk to someone older or someone you respect: a teacher, a customer, a friend's parents. Dạ, em hiểu rồi. Yes, I understand. When someone calls your name, Dạ? means "Yes?"

It also opens almost any polite reply, even a no: Dạ, không. No. Dạ, em chưa ăn. No, I haven't eaten yet. Starting with dạ makes the rest sound respectful, so in Saigon you'll hear it all day long.

In Hà Nội the polite yes is mostly vâng, often together as dạ vâng. Saigon speakers understand vâng, and you'll see it in books, but in conversation they mostly say dạ.

To friends your age, to younger people and to people you're very close to, the casual yes is ừ, or ờ in Saigon: Ừ, mai gặp nha. Yeah, see you tomorrow. Don't say ừ to someone older you're not close to; it sounds rude.

On its own, dạ can mean yes, but often it only means "I'm listening". To make the answer clear, add có, rồi or the verb: Dạ, có. Dạ, rồi.