Learn Hardcore Vietnamese: Tuần trước, tôi đã viết thư cho An.

In Vietnamese, time expressions often come at the front to set the scene. It’s not strictly required—you could say Tôi đã viết thư cho An tuần trước—but fronting Tuần trước emphasizes “last week.” The comma after a fronted time phrase is optional and mainly for clarity in writing, not pronunciation.

What does đã do in this sentence? How do we express past tense in Vietnamese?

Vietnamese verbs don’t conjugate for tense. Instead, particles like đã mark completed (past) actions. Placing đã before the verb viết tells you “wrote” or “have written.” Without đã, context (e.g., “tuần trước”) still suggests past, but đã makes it explicit. Other particles include đang for ongoing actions and sẽ for future.

Why is there no article or classifier before thư (“letter”)? Shouldn’t we say một bức thư?

In fixed expressions like viết thư (“to write a letter”), Vietnamese often omits numerals and classifiers when the exact number isn’t important. If you want to stress that it’s one specific letter, you can add them: viết một bức thư. Here, however, viết thư simply means “write (a) letter” in general.

What is the function of cho here? Are there other ways to indicate the recipient?

Cho means “for” and marks the recipient or beneficiary of an action. In viết thư cho An, it means “write a letter to An.” You could also say gửi thư cho An (“send a letter to An”), but you still need cho to introduce the recipient. Omitting cho (e.g., viết thư An) is ungrammatical.

Can we rearrange the sentence as Tôi đã viết cho An thư?

No. The normal order is Subject – Verb – Direct Object – Indirect Object. Here, thư is the direct object and cho An the indirect object. So it must be viết thư cho An, not viết cho An thư.

Why is the subject tôi used? Can we use another pronoun?

Tôi is the neutral, polite first-person pronoun, safe in almost any context. Vietnamese has many pronouns (mình, tớ, anh, em, tao, etc.), and choice depends on formality, age, status, and the relationship between speakers. If you’re talking to a friend, you might choose mình or tớ, but tôi works universally.

What’s the difference between using đã and ending the sentence with rồi, as in Tôi viết thư cho An rồi?

Both indicate a completed action. The difference is placement and nuance:

Đã goes before the verb (đã viết) and is more formal or neutral.
Rồi typically comes at the end of the sentence and is common in speech for “already.”
So Tôi đã viết thư cho An and Tôi viết thư cho An rồi both mean “I’ve already written (a) letter to An,” but rồi has a slightly more conversational feel.

Are there other ways to say “last week” besides Tuần trước?

Yes. You can use:

Tuần vừa rồi (the week just gone)
Tuần rồi (colloquial)
All mean “last week,” but Tuần trước sounds a bit more formal than Tuần rồi. For “the other day,” you might say hôm trước, and for “yesterday,” hôm qua.