đã

The basic structure is: Subject + đã + Verb.

Vietnamese verbs do not conjugate for tense. Instead, đã is used to mark that an action has occurred or been completed. Because Vietnamese relies on aspect rather than tense, đã is not a mandatory grammatical rule. If the past context is already obvious from a time word (like hôm qua / yesterday), native speakers usually drop đã entirely in casual speech. When dropping đã in affirmative past-tense sentences, native speakers often replace it with có before the verb. Note that có is not just a neutral past-tense replacement; it specifically adds an affirmative emphasis exactly like the English emphatic 'did' (e.g., Hôm qua tôi có đi làm / Yesterday I did go to work). Note that there is a regional difference: Southern Vietnamese speakers drop đã almost constantly in casual speech, relying on context or rồi, whereas Northern Vietnamese speakers are much more likely to retain đã in everyday spoken conversation.

To form negative statements about the past, native speakers typically just use không (did not) or chưa (not yet) and drop đã. Using đã không is generally unnatural in everyday conversation, although you will still encounter it frequently in writing, traditional textbooks, or formal news broadcasts. There is one major exception where it is used in speech: it is perfectly natural and common in conditional sentences to mean "would not have" or "did not" (e.g., Nếu tôi biết, tôi đã không làm / If I had known, I would not have done it).

For questions asking "Have you [verb] yet?", use Subject + đã + Verb + chưa? Just like in affirmative statements, đã is often dropped in casual questions (e.g., Bạn ăn chưa? instead of Bạn đã ăn chưa?). To answer negatively, simply say Chưa (Not yet). However, for simple past questions about a specific time (e.g., "Did you go to work yesterday?"), use the Yes-No Question pattern (e.g., Hôm qua bạn có đi làm không?) and answer negatively with Không.

Learners often confuse đã with rồi (already). Here is the difference:

• Đã goes before the verb and focuses on the occurrence of the action.
• Rồi goes after the verb or at the end of the sentence and focuses on completion.

They are frequently used together for extra emphasis: Tôi đã ăn rồi (I have already eaten).

Note: You might also see đã in a few other contexts:

• At the end of a clause: (e.g., Ăn đã). In this position, it means "first" or "for now" (Let Me Do This First).
• Past experience: Combined with từng (Have Ever Done), it means "have ever" (e.g., Tôi đã từng đi Nhật / I have been to Japan).
• As an adjective: It can mean "satisfying" or "great" (e.g., Đã quá! / So satisfying!).
• Emphatic denial: Used with đâu (Not At All) to strongly deny something (e.g., Tôi đã ăn đâu! / I haven't eaten at all!).
• Before an adjective: It can mean "already" when describing a state (e.g., Trời đã muộn / It is already late).