Tớ đồng ý sau khi cậu đổi ý.

Tớ means I / me, and cậu means you, but these are not neutral pronouns for every situation.

This pair is commonly used between:

• friends
• classmates
• people of similar age
• people speaking in a casual, familiar way

So the sentence sounds friendly and informal. It would not usually be the best choice for:

• speaking to a teacher
• speaking very politely
• talking to someone much older or higher in status

A learner should think of tớ – cậu as a matched pronoun pair often used in close, casual conversation.

In Vietnamese, đồng ý is the normal expression for to agree.

• đồng = same / together
• ý = idea / opinion

Together, đồng ý literally gives the idea of sharing the same opinion, and in real usage it simply means agree or consent.

It functions as a verb phrase, so Tớ đồng ý = I agree / I agreed depending on context.

Sau khi means after and introduces a clause.

Structure:

• sau khi + subject + verb

So here:

• sau khi cậu đổi ý = after you changed your mind

This is a very common pattern in Vietnamese for time relationships between two actions.

Examples:

• Sau khi ăn, tớ đi học. = After eating, I went to school.
• Sau khi cậu gọi, tớ mới biết. = After you called, I only then knew.

In your sentence, sau khi tells us that the action agreeing happened later than the action changing one’s mind.

Yes, đổi ý is a very common fixed expression meaning to change one’s mind.

Literally:

• đổi = change
• ý = idea / opinion / intention

So đổi ý is not just any random combination of words; it is a standard everyday phrase.

You will often hear:

• Tôi đổi ý rồi. = I changed my mind.
• Cậu đổi ý à? = Did you change your mind?

Vietnamese verbs do not change form for tense the way English verbs do.

So:

• đồng ý can mean agree, agreed, or will agree
• đổi ý can mean change one’s mind, changed one’s mind, or will change one’s mind

Time is usually understood from:

• context
• time words
• particles
• the relationship between events

In this sentence, sau khi shows the sequence of events, and the intended meaning tells us this is past: first cậu đổi ý, then tớ đồng ý.

If you wanted to make the past more explicit, you could say:

• Tớ đã đồng ý sau khi cậu đổi ý.
• Tớ đồng ý sau khi cậu đã đổi ý.

Both are possible, though Vietnamese often leaves such markers out when the meaning is already clear.

Yes. Đã is often used to mark a past event or completed action more clearly.

Possible versions:

• Tớ đã đồng ý sau khi cậu đổi ý.
• Tớ đồng ý sau khi cậu đã đổi ý.
• Tớ đã đồng ý sau khi cậu đã đổi ý.

These all work, but they are not always necessary.

In everyday Vietnamese, if the time relationship is already obvious, speakers often omit đã. That is why the original sentence is perfectly natural.

It can come first.

Original:

• Tớ đồng ý sau khi cậu đổi ý.

Also possible:

• Sau khi cậu đổi ý, tớ đồng ý.

Both mean the same thing, but the focus is slightly different:

• putting Tớ đồng ý first foregrounds the main action
• putting Sau khi cậu đổi ý first foregrounds the time condition or sequence

Vietnamese is fairly flexible with this kind of time clause placement.

By itself, it mainly states the sequence:

• first you changed your mind
• then I agreed

In many contexts, listeners may naturally infer something like I didn’t agree until after you changed your mind, but that stronger sense is not fully forced by the sentence alone.

If you want to emphasize only then, Vietnamese often uses words like:

• mới
• chỉ

For example:

• Tớ mới đồng ý sau khi cậu đổi ý.
• Tớ chỉ đồng ý sau khi cậu đổi ý.

These make the idea of not before that point stronger.

Yes. That is very normal.

Đồng ý can be used:

• on its own: Tớ đồng ý. = I agree.
• with an object or idea:
  • Tớ đồng ý với cậu. = I agree with you.
  • Tớ đồng ý chuyện đó. = I agree to that / accept that.

In your sentence, the thing being agreed to is left understood from context, which is completely natural in conversation.

Because cậu is not the person being agreed with here. It is the subject of the second clause.

Compare:

1. Tớ đồng ý với cậu.

   • with you
   • here cậu is the person whose opinion you agree with

2. Tớ đồng ý sau khi cậu đổi ý.

   • after you changed your mind
   • here cậu is the subject of đổi ý

So in your sentence, cậu belongs to the time clause, not to đồng ý với.

Yes, it is natural and understandable.

It sounds like casual spoken Vietnamese between people who know each other well. The only thing that could change is style or emphasis.

For example:

• Tớ đồng ý sau khi cậu đổi ý. = natural, straightforward
• Sau khi cậu đổi ý, tớ đồng ý. = also natural
• Tớ chỉ đồng ý sau khi cậu đổi ý. = more emphatic: I only agreed after you changed your mind

So the original sentence is a normal colloquial sentence.

The tones matter a lot here:

• tớ — rising tone
• đồng — low falling tone
• ý — rising tone
• sau — level tone
• khi — level tone
• cậu — heavy / low glottalized tone
• đổi — dipping/asking tone
• ý — rising tone

A few pronunciation notes:

• đ is not the same as English d; it is closer to a regular d sound, while Vietnamese d is different depending on dialect.
• ơ in tớ is a different vowel from English o.
• ậu in cậu is a diphthong and should not be pronounced like English cow, though it may sound somewhat similar to learners.
• đổi ý has two consecutive syllables with clear tones, so do not flatten them.

If a learner says the words with English stress instead of Vietnamese tones, the sentence may be hard to understand.