Tớ thấy một vết bẩn trên áo sơ mi.

Tớ means I / me, but it is informal and fairly friendly.

Native speakers often use tớ when talking to:

• friends
• classmates
• people of similar age
• someone they are close to

It would sound less natural in very formal situations. In those cases, you might hear:

• tôi = more neutral/formal I
• mình = friendly/soft I, depending on relationship
• other pronouns depending on age and social relationship

So Tớ thấy một vết bẩn trên áo sơ mi sounds like something you might say casually to a friend.

Thấy usually means to see, to notice, or to find by seeing.

In this sentence, it means something like:

• I see
• I notice
• I spot

So the sentence suggests that the speaker notices a stain on the shirt.

A useful comparison:

• thấy = to see/notice
• nhìn = to look at

For example:

• Tớ thấy một vết bẩn = I notice a stain.
• Tớ nhìn áo sơ mi = I look at the shirt.

So thấy focuses on the result of seeing, not just the act of looking.

Yes, một often works like a/an in sentences like this, although its basic meaning is one.

So:

• một vết bẩn = a stain / one stain

Vietnamese does not have articles exactly like English, so một is commonly used when introducing a single countable thing.

In many situations:

• một can sound like a/an
• but it can also emphasize one

Here it most naturally means a stain.

Bẩn by itself means dirty.

Vết bẩn means a stain, a dirty mark, or a spot.

So:

• bẩn = dirty
• vết bẩn = stain / dirty mark

You use vết bẩn when you want to talk about a specific mark on a surface, piece of clothing, wall, paper, and so on.

Examples:

• Áo này bẩn. = This shirt is dirty.
• Áo này có một vết bẩn. = This shirt has a stain.

So in your sentence, the speaker is not just saying the shirt is dirty in general, but that there is a particular stain.

It behaves a bit like one in some contexts, but it is better to think of vết here as a noun meaning mark, trace, or streak.

In vết bẩn:

• vết = mark/spot
• bẩn = dirty

Together they form the noun phrase stain.

Vietnamese has many words like this where a concrete noun combines with another word to create a natural expression. So while vết may feel classifier-like, in this sentence it is part of the vocabulary item vết bẩn.

Other similar expressions:

• vết mực = ink stain
• vết máu = blood stain
• vết cắt = cut mark

In this sentence, trên means on.

So:

• trên áo sơ mi = on the shirt

Yes, trên often means:

• on
• above
• over

Its exact translation depends on context.

Examples:

• trên bàn = on the table
• trên tường = on the wall
• trên trời = in the sky / up in the sky

In your sentence, it marks the location of the stain: the stain is on the shirt.

Áo is a general word for shirt, top, or garment.

Áo sơ mi is more specific: it means a dress shirt, button-up shirt, or simply shirt in the sense of a collared shirt.

So:

• áo = shirt/top/clothing item in a broad sense
• áo sơ mi = shirt, especially a button-up style

If you just said áo, the meaning would be less specific.

The word order is very close to English:

• Tớ = I
• thấy = see/notice
• một vết bẩn = a stain
• trên áo sơ mi = on the shirt

So literally, it is:

I see a stain on the shirt.

This is a good example of Vietnamese often following a straightforward Subject + Verb + Object pattern.

You can, but it changes the feel.

• Tớ thấy một vết bẩn trên áo sơ mi = I see a stain on the shirt.
• Tớ thấy vết bẩn trên áo sơ mi = I see the stain / I see stain marks on the shirt, depending on context

Leaving out một can make the noun phrase sound more definite or more context-dependent. For a learner, một vết bẩn is the clearest and most natural way to say a stain.

Vietnamese does not use articles the same way English does.

English needs:

• a stain
• the shirt

Vietnamese often leaves article-like meaning to context. So:

• áo sơ mi can mean a shirt, the shirt, or just shirt, depending on the situation

In this sentence, English naturally translates it as the shirt, but Vietnamese does not need a separate word for the.

A common more neutral version would be:

Tôi thấy một vết bẩn trên áo sơ mi.

Here, tôi replaces tớ.

Compare:

• Tớ thấy một vết bẩn trên áo sơ mi. = casual, friendly
• Tôi thấy một vết bẩn trên áo sơ mi. = neutral/formal

The rest of the sentence stays the same.

A rough guide:

• tớ: short, with a rising tone
• thấy: rising tone
• một: often pronounced more like một/mốt in connected speech depending on region and pace
• vết: rising tone
• bẩn: falling-glottal kind of tone in the North
• trên: level-ish tone
• áo: rising diphthong-like sound
• sơ: level tone
• mi: level tone

The tones matter a lot, especially in words like:

• tớ
• thấy
• vết
• bẩn

If you are learning Northern Vietnamese, try listening carefully to native audio, because tones are easier to copy than to learn only from written descriptions.

Yes, you can say:

Tớ nhìn thấy một vết bẩn trên áo sơ mi.

This also means I see / I can see a stain on the shirt.

The difference is:

• thấy = notice/see
• nhìn thấy = literally look and see, often emphasizing visible perception a bit more

In many everyday situations, both are natural.
But thấy is simpler and very common.

Yes. By itself, áo sơ mi just means shirt. The owner is not specified.

So the sentence could mean:

• I see a stain on the shirt.
• I see a stain on your shirt.
• I see a stain on his shirt.
• I see a stain on my shirt.

If you want to specify ownership, you can add it:

• trên áo sơ mi của tớ = on my shirt
• trên áo sơ mi của cậu = on your shirt
• trên áo sơ mi của anh ấy = on his shirt

So the original sentence leaves that detail to context.