Rúguǒ yīfu bù héshēn, wǒ jiù xiǎng tuìhuò.

This pattern means if..., then....

So:

• 如果 = if
• 就 = then / in that case

In 如果衣服不合身，我就想退货, the structure is:

• 如果衣服不合身 = if the clothes don’t fit
• 我就想退货 = then I want to return them

A very common Chinese pattern is:

如果 + condition, 就 + result

Even though English does not always need then, Chinese often uses 就 to clearly connect the result to the condition.

Yes, you can say 如果衣服不合身，我想退货 and it is still understandable.

But 就 is very natural because it highlights the result of the condition:

• 如果衣服不合身，我就想退货。
  = If the clothes don’t fit, then I want to return them.

Without 就, the sentence is still correct, but slightly less explicitly structured as if... then....

So:

• 如果..., 就... = very common and textbook-clear
• 如果...,... = also possible in natural speech

合身 means to fit well, especially for clothing.

It usually refers to whether clothes fit your body properly:

• not too big
• not too small
• the shape/size is right for you

So 衣服不合身 means:

• the clothes don’t fit
• the clothing is not the right fit

This is a very common word for clothes. It is more specific than a general word like 适合, which means to suit / to be suitable for.

Compare:

• 这件衣服很合身。 = This piece of clothing fits well.
• 这个颜色很适合你。 = This color suits you.

Because 合身 describes a state/quality, so 不 is the normal negation.

• 合身 = to fit / be fitting
• 不合身 = not fit / not fitting properly

In Chinese:

• 不 is usually used to negate adjectives, states, habits, and general facts
• 没(有) is usually used for did not or have not

Since this sentence is talking about whether the clothes fit, not whether some fitting action happened in the past, 不合身 is the natural form.

衣服 can refer to clothes/clothing in a general sense, and Chinese often does not mark singular vs. plural the way English does.

So depending on context, 衣服 could mean:

• clothes
• the clothing
• a garment / an item of clothing

In this sentence, English might translate it as the clothes or the item of clothing, depending on the situation.

If you wanted to be more specific, you could say:

• 这件衣服 = this piece of clothing
• 这些衣服 = these clothes

So the original sentence is natural because Chinese often leaves that number distinction to context.

Because 衣服 here is being used in a general way, not as one specific item counted out.

Measure words are used when you specify quantity or point to an item, for example:

• 一件衣服 = one piece of clothing
• 这件衣服 = this piece of clothing
• 那件衣服 = that piece of clothing

But in 如果衣服不合身, the speaker is just talking about clothing as the thing being discussed, so no measure word is needed.

Here 想 means something like want to or feel like.

So:

• 我想退货 = I want to return it / I’m thinking of returning it

This is softer than 要.

Compare:

• 我想退货 = I want to return it / I’m considering returning it
• 我要退货 = I want to return it / I am going to return it

In many situations, 想 sounds less direct and a bit more polite or less forceful than 要.

So in this sentence, 想 suggests the speaker’s intention or desire, not just a literal thought process.

No, they are related but not the same.

• 退货 = return goods / return a product
• 退款 = refund money

So:

• 我想退货 = I want to return the item
• 我想退款 = I want a refund

Often, returning goods and getting a refund happen together, but the words focus on different things:

• 退货 focuses on giving the product back
• 退款 focuses on getting the money back

The comma separates the condition from the result:

• 如果衣服不合身， = if the clothes don’t fit,
• 我就想退货。 = then I want to return them.

This kind of pause is very common in Chinese when a sentence begins with a conditional clause.

It works much like English:

• If it doesn’t fit, I want to return it.

So the comma helps show the sentence structure clearly.

Yes, you might hear that in conversation if the subject is already obvious from context.

Chinese often drops subjects when they are clear.

So:

• 如果衣服不合身，我就想退货。 = fully explicit
• 如果衣服不合身，就想退货。 = natural if everyone knows who is doing the returning

However, keeping 我 makes the sentence clearer, especially for learners and in stand-alone examples.

A little, but it is very logical.

The order is:

1. 如果
   • condition
2. main clause with 就
3. verb phrase at the end

So:

• 如果衣服不合身 = if the clothes don’t fit
• 我就想退货 = I then want to return them

This is actually quite close to English If..., then... order.

A useful way to remember it is:

如果 + situation, subject + 就 + response

Here it is pronounced bù.

That is because the tone-change rule for 不 happens mainly before a fourth-tone syllable:

• before a 4th tone: 不 changes from bù to bú
• otherwise, it usually stays bù

In 不合身, the next syllable is hé (second tone), so it stays:

• bù héshēn

Example of the tone change:

• 不对 → bú duì

But here:

• 不合身 → bù héshēn

Yes. 要是 also means if, and it is very common in spoken Chinese.

So you could say:

• 要是衣服不合身，我就想退货。

The difference is mainly in tone/register:

• 如果 = a bit more neutral/formal
• 要是 = more conversational

Both are correct and natural.