deowoseo changmuneul yeoreo nohasseoyo.

-아서/어서 is a very common ending that can mean because, so, or simply connect two actions/events.

In this sentence, 더워서 means because it was hot or since it was hot.

• 덥다 = to be hot
• 더워서 = because it is/was hot

So the first part gives the reason for the second part: It was hot, so...

This is because 덥다 is a ㅂ-irregular adjective/verb.

When a ㅂ-irregular word is followed by a vowel-starting ending like -어서, the ㅂ changes to 우, and then it combines naturally:

• 덥다
• 덥 + 어서 → not used like that
• 더우어서 → contracts to 더워서

So:

• 덥다 → 더워요
• 덥다 → 더워서

This same pattern appears in words like:

• 춥다 → 추워요
• 어렵다 → 어려워요

열어 놓았어요 means something like:

• opened it and left it that way
• left it open
• opened it in advance / for the time being and kept it open

The grammar is:

• 열다 = to open
• 열어 놓다 = to open and leave in that state
• 열어 놓았어요 = did that in the past / have left it open

So this is not just the action of opening. It emphasizes the resulting state: the window is open because someone opened it and intentionally left it open.

This is one of the most important differences in the sentence.

• 창문을 열었어요 = I opened the window.
• 창문을 열어 놓았어요 = I opened the window and left it open.

So -아/어 놓다 adds the idea of:

• keeping the result of the action,
• leaving something in a certain state,
• sometimes doing something in preparation.

In this sentence, 열었어요 would only tell you that the window was opened.
열어 놓았어요 tells you it was opened and remains open.

Originally, yes, 놓다 literally means to put down / place. But in grammar patterns like -아/어 놓다, it has developed a more grammatical meaning.

Here, 놓다 does not mean literally putting something somewhere.
Instead, -아/어 놓다 means:

• do something
• and leave it in that condition

So in 열어 놓았어요, 놓다 functions more like an auxiliary verb than its literal dictionary meaning.

Great question. In Korean, past tense can describe a completed action that has a present result.

So 열어 놓았어요 means:

• the action of opening-and-leaving-open happened already,
• and the result may still be true now.

That is why this often sounds natural in English as:

• I left the window open
• I’ve left the window open

The past tense marks when the action was done, not necessarily that the state is over.

Because 창문 is the direct object of 열다.

• 창문을 열다 = to open the window

Here:

• 창문 = window
• 을 = object marker

So 창문을 shows that the window is the thing being opened.

If you used 창문이, it would shift the grammar and meaning. For example:

• 창문이 열렸어요 = The window opened / The window is open

That version focuses on the window as the subject, often with a more passive/intransitive feeling.

But in your sentence, someone intentionally opened it, so 창문을 열어 놓았어요 is the natural choice.

The subject is omitted, which is very normal in Korean.

더워서 창문을 열어 놓았어요 most naturally means something like:

• I left the window open because it was hot
• or We left the window open because it was hot

Korean often leaves out the subject when it is obvious from context.
Because the verb ending -어요 is polite but not tied to a specific subject, you need context to know exactly who did it.

In many everyday situations, English would require I, but Korean often does not say it.

Both can work, but they feel a little different.

• 더워서 창문을 열어 놓았어요 = Because it was hot, I left the window open.
• 더우니까 창문을 열어 놓았어요 = Since it was hot, I left the window open.

In many cases they are close, but:

• -아서/어서 often sounds like a natural reason or cause
• -(으)니까 often sounds a bit more like the speaker’s reasoning, judgment, or justification

So 더워서 sounds very natural here because it simply states the cause.

It is in the polite informal style, often called the -요 form.

So this is appropriate for:

• everyday conversation
• speaking politely to someone you do not know well
• speaking to coworkers, acquaintances, customers, etc.

The plain dictionary-style breakdown is:

• 열어 놓다 = to leave open
• 열어 놓았어요 = polite past

Other styles would be:

• 열어 놓았어 = casual
• 열어 놓았습니다 = more formal

Yes. In everyday spoken Korean, 놓았어요 is often contracted.

So you may hear:

• 열어 놓았어요 → careful/full form
• 열어 놨어요 → very common spoken form

Both mean the same thing.

Likewise:

• 해 놓았어요 → 해 놨어요
• 켜 놓았어요 → 켜 놨어요

As a learner, it is good to recognize both forms.