hãy

1. Placement and Form
Because Vietnamese has no verb conjugation, hãy simply sits immediately before the main verb to turn the sentence into a command. It never changes form. While public signs and written instructions frequently use subject omission, keeping the pronoun (like anh, chị, or em) is the grammatical default in interpersonal communication to avoid sounding abrupt.

2. Formal and Written Register
You will frequently see hãy on public signs, in written instructions, manuals, and advertisements. However, in everyday casual conversation, it is almost entirely dropped. Using it with friends will make you sound unnaturally stiff or like you are delivering a theatrical speech.

3. Not a Polite "Please"
Many learners confuse hãy with the English "please" because it appears in translated instructions. However, hãy does not ask for a favor; it acts as an authoritative instruction, earnest advice, or official request. For interpersonal warmth, native speakers use làm ơn or add the softening particle nhé. That said, hãy is also frequently used to mean "Let's [do something]" when paired with cùng or cùng nhau, when using an inclusive pronoun like chúng ta (e.g., Chúng ta hãy bắt đầu), or when paired with the final particle nào (e.g., Chúng ta hãy đi nào!).

4. Contrast and Stacking with "đi"
For casual, everyday commands, native speakers often use the final particle đi at the end of the sentence. While hãy is more formal, the two are not mutually exclusive; they can stack together in the same sentence (Hãy + Verb + đi) to combine a formal command with a nudge of encouragement.

5. The Negative Counterparts
While hãy tells someone to do something, its everyday negative equivalent is đừng (don't), which sits in the exact same position before the verb. However, on public signs and in written rules where hãy is most common, the formal negative equivalents are không được (not allowed to) or cấm (prohibited).

6. The Adverb "hãy còn"
Note that hãy also has a secondary meaning as an adverb meaning "still" or "yet," most commonly seen in the phrase hãy còn (still). This is completely separate from its use as an imperative marker, and serves as a more literary or regional (Southern) alternative to the much more common everyday phrase vẫn còn.