Learn Hardcore Vietnamese: Cái áo màu đỏ này rất sạch.

Here, rất sạch works like a verb phrase meaning “is very clean”.
You would not say Cái áo màu đỏ này là rất sạch in normal speech; that sounds unnatural or emphatic in a weird way.

là is used mainly:

before nouns/pronouns:
- Đây là áo của tôi. = This is my shirt.
sometimes in cleft or emphatic structures.

But with a simple adjective (sạch, đẹp, to, nhỏ), Vietnamese normally drops “to be” and just uses the adjective (optionally with rất, lắm, etc.).

What does cái mean in cái áo? Is it necessary?

cái is a classifier (measure word). Vietnamese usually needs a classifier when a common noun refers to a specific, countable thing.

áo = shirt / clothing in general
cái áo = the specific shirt (one item)

In this sentence, you’re talking about this particular shirt, so you use a classifier:

Cái áo màu đỏ này rất sạch. = This red shirt is very clean.

In casual speech, people sometimes drop classifiers, especially in short phrases or when the context is very clear, but:

In a full sentence like this, cái sounds natural and standard.
Without cái (Áo màu đỏ này rất sạch), it’s still understandable, but it can sound a bit less natural or like a heading/caption.

What is the difference between áo and cái áo?

áo by itself is more like the bare noun “shirt/clothing” in general or in a generic sense:
- Mặc áo đi. = Put on a shirt / Put on your shirt.
cái áo is one specific shirt (classifier + noun):
- Cái áo của tôi = my (specific) shirt.

In Cái áo màu đỏ này rất sạch., you are clearly talking about a particular shirt that you can point at, so cái áo is more appropriate than just áo.

Why do we say màu đỏ instead of just đỏ? Is there a difference between áo đỏ and áo màu đỏ?

Both are correct, and both mean “red shirt”, but there’s a nuance:

áo đỏ
- literally: red shirt
- short, common, very natural.
áo màu đỏ
- literally: shirt [with the] color red
- slightly more explicit that you’re talking about the color.

In everyday speech:

áo đỏ is often enough.
áo màu đỏ can sound a bit more descriptive or neutral, and is very common too.

In your sentence:

Cái áo đỏ này rất sạch.
Cái áo màu đỏ này rất sạch.

Both are acceptable. Many speakers would use them interchangeably here.

Why is the word order cái áo màu đỏ này and not something like cái áo này màu đỏ or này cái áo màu đỏ?

Vietnamese noun phrase order is generally:

classifier + noun + (adjectives, including colors) + demonstrative

So:

cái (classifier)
áo (noun)
màu đỏ (adjective phrase: red-colored)
này (demonstrative: this)

→ cái áo màu đỏ này

Your suggested variants:

cái áo này màu đỏ
- This is actually two parts:
  - noun phrase: cái áo này = this shirt
  - predicate: màu đỏ = (is) red
- Example full sentence:
  - Cái áo này màu đỏ và rất sạch.
    = This shirt is red and very clean.
- So it’s a different structure, not wrong, but not the same as the original.
này cái áo màu đỏ
- This is ungrammatical.
- Demonstratives like này, đó, kia normally come at the end of the noun phrase, not at the start.

So for a simple noun phrase “this red shirt”, the normal order is:

cái áo đỏ này or cái áo màu đỏ này.

What exactly does này mean, and how is it different from đó and kia?

These are all demonstratives (this/that):

này ≈ this (near the speaker)
- cái áo này = this shirt
đó ≈ that (near the listener or a bit away)
- cái áo đó = that shirt
kia ≈ that (over there) (farther away / pointing)
- cái áo kia = that shirt over there

Position in the noun phrase:

classifier + noun (+ adjective) + này/đó/kia

Examples:

cái áo đỏ này = this red shirt
cái áo xanh đó = that blue shirt
cái áo mới kia = that new shirt over there

In your sentence, này tells us the shirt is “this one (near me/us)”.

What does rất mean, and can I leave it out?

rất means “very”.

Cái áo màu đỏ này rất sạch.
= This red shirt is very clean.

Yes, you can leave it out:

Cái áo màu đỏ này sạch.
= This red shirt is clean.

Differences:

With rất: stronger, more emphatic – the shirt is quite / very clean.
Without rất: simple statement of fact – it’s clean, not dirty.

Other common intensifiers:

lắm (usually at the end): Cái áo này sạch lắm. = This shirt is very clean.
cực kỳ, vô cùng (very, extremely), etc., in more expressive speech.

Can I say Cái áo màu đỏ này sạch lắm instead? What’s the difference between rất and lắm?

Yes, you can say:

Cái áo màu đỏ này sạch lắm.
= This red shirt is very clean.

rất and lắm both mean roughly “very”, but:

rất comes before the adjective:
- rất sạch
lắm comes after the adjective:
- sạch lắm

Nuance:

rất is a bit more neutral / standard, widely used in both spoken and written language.
lắm often feels a bit more colloquial / expressive, common in speech.

In many contexts, they are interchangeable in meaning; it’s mostly style and rhythm.

Do adjectives like sạch always come after the noun in Vietnamese?

Inside a noun phrase, yes: adjectives normally follow the noun.

Order pattern:

classifier + noun + adjective(s) + demonstrative

Examples:

cái áo sạch = the clean shirt
căn phòng sạch = the clean room
cái áo màu đỏ sạch (a bit odd; more natural: rất sạch in predicate)

But in your sentence, sạch is not inside the noun phrase; it’s the predicate (like a verb):

Cái áo màu đỏ này (subject)
rất sạch (predicate: “is very clean”)

So:

As part of the noun phrase: áo sạch = clean shirt
As the predicate: (cái) áo… sạch = the shirt is clean

Both positions exist, but inside the noun phrase, adjectives follow the noun.

How would I say “These red shirts are very clean”? How do I make cái áo plural?

To show plurality, Vietnamese often uses những (or sometimes các) before the classifier:

những cái áo màu đỏ này rất sạch.
= These red shirts are very clean.

Structure:

những = plural marker (“some/several/these”)
cái áo màu đỏ này = this red shirt
→ Together: những cái áo màu đỏ này = these red shirts

Notes:

những is common, slightly more informal/neutral.
các is often used for a clearly defined, complete group (more formal/collective):
- Các áo màu đỏ này rất sạch. (still more natural with the classifier: các cái áo…, though people might drop it in casual speech)

Spoken Vietnamese often relies on context for singular/plural, so in everyday conversation, people might just say:

Áo màu đỏ này rất sạch.
and let context tell you whether it’s one shirt or several.

Is cái the only classifier I can use with áo, or can I say chiếc áo too?

You can use both cái and chiếc with áo.

cái áo
- very common, neutral, everyday speech.
chiếc áo
- a bit more formal, literary, or descriptive; can sound slightly more elegant or emotional.

Examples:

Cái áo màu đỏ này rất sạch. (neutral, everyday)
Chiếc áo màu đỏ này rất sạch. (a bit more literary or “written” in tone)

Meaning difference is minimal; it’s mostly style.
For daily conversation, cái áo is perfectly natural.

How should I pronounce sạch? Is it similar to sách?

They are different words with different final consonants and tones:

sạch
- final consonant: -ch (like “tch” in “match”, but shorter and unreleased)
- tone: nặng (heavy, low and abrupt, with a glottal stop feel)
- meaning: clean
sách
- final consonant: also -ch, but the vowel and tone differ
- tone: sắc (rising tone)
- meaning: book

Key points for sạch:

Start low in pitch, then drop sharply and cut off.
Final -ch is brief, no release of air (stop the sound at the palate).

If you mispronounce the tone, you might be understood from context, but tone is important, so practice saying:

sạch, sạch, rất sạch
slowly, then faster, keeping that low, heavy, cut-off tone.