Tôi phải về trước.

A natural breakdown is:

• Tôi = I
• phải = must / have to
• về = go back / go home / leave
• trước = first / earlier / before others

So the structure is basically:

subject + modal verb + main verb + time/order word

That is why Tôi phải về trước means something like I have to leave first or I have to go home earlier than the others.

Here, phải shows necessity or obligation. It is stronger than should.

So:

• phải = must / have to
• nên = should / ought to

In this sentence, phải suggests that the speaker does not really have a choice, or at least feels they do not.

Also, phải can mean other things in other contexts, but in Tôi phải về trước, it is clearly a modal verb meaning must / have to.

It can mean either, depending on context.

Common possibilities:

• go home
• go back
• head back
• sometimes just leave in natural English

In everyday conversation, if someone says Tôi phải về trước at a meal, party, or meeting, listeners often understand it as I have to head home first or simply I have to leave first.

Vietnamese often leaves some details unstated when the context is clear.

Because trước here describes when / in what order the action happens.

So về trước means:

• leave before others
• go back earlier
• go first

Putting trước after the verb is very normal in Vietnamese.

Compare:

• Tôi phải về. = I have to go home / I have to leave.
• Tôi phải về trước. = I have to leave first / earlier than the others.

So trước adds the idea of before other people or earlier than expected.

They are similar, but not identical.

• về trước = leave before others / go back first
• về sớm = go home early

So:

• trước focuses on order relative to other people or events
• sớm focuses on early time

For example:

• Tôi về trước nhé. = I’m heading off first, okay?
• Hôm nay tôi về sớm. = Today I’m going home early.

Sometimes both can sound similar in English, but the nuance in Vietnamese is slightly different.

Yes, you often can, especially in conversation.

Vietnamese frequently drops the subject when it is obvious from context.

So both are possible:

• Tôi phải về trước. = explicit I
• Phải về trước. = Have to leave first / I have to leave first, with I understood

Keeping tôi makes the sentence clearer and a bit more complete. Dropping it sounds more conversational when everyone already knows who is speaking.

This is a very common question.

• về trước suggests going back, often going home
• đi trước means leave/go first more generally

So:

• Tôi phải về trước. = I have to head back / go home first
• Tôi phải đi trước. = I have to leave first

At a gathering, both can work, but đi trước focuses more on departing from the current place, while về trước often suggests returning home or heading back somewhere.

If you want the most neutral I have to leave first, đi trước is often safer. If you want the sense of I’m heading home, về trước fits well.

Yes, it is grammatical and natural, but by itself it can sound a little plain or direct, depending on the situation.

Vietnamese often softens this kind of sentence with extra words. For example:

• Tôi xin phép về trước. = Please excuse me, I’ll leave first.
• Mình về trước nhé. = I’m heading off first, okay?
• Em phải về trước ạ. = polite, depending on who you are speaking to

A few notes:

• xin phép makes it more polite
• nhé makes it softer and friendlier
• ạ adds politeness
• tôi is neutral, but not always the most natural pronoun in casual social situations

So if you are speaking to friends, coworkers, or older people, you will often hear a softer version rather than just Tôi phải về trước.

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

So phải về does not itself tell you:

• present
• future
• past

The time is usually understood from context or added with time words.

Examples:

• Bây giờ tôi phải về trước. = I have to leave first now.
• Lát nữa tôi phải về trước. = Later I’ll have to leave first.
• Hôm qua tôi phải về trước. = Yesterday I had to leave first.

Without a time word, listeners usually understand it from the situation.

A rough guide is:

• Tôi ≈ like toy, but with Vietnamese vowel quality
• phải ≈ somewhat like fai, with a dipping/rising tone
• về ≈ somewhat like veh, with a falling tone
• trước ≈ roughly troo-uhk or trɨək, with a rising tone and a final unreleased -c/-k

A few pronunciation points:

• ph in Vietnamese sounds like f
• tr is not the same as English ch
• ươ in trước is a vowel combination that English does not really have
• the tones matter a lot for being understood

If you are learning pronunciation, the hardest part here is usually trước.