Zatvori prozor, jer je sada hladno.

Zatvori is the imperative form, used to give a command or instruction. In this sentence, it means close.

More specifically, it is:

• 2nd person singular imperative
• used when speaking to one person informally

So:

• Zatvori prozor. = Close the window.

If you were speaking formally to one person, or to several people, you would usually say:

• Zatvorite prozor. = Close the window.

In Serbian, subject pronouns are often left out when they are already clear from the verb form.

The verb zatvori already tells you that the command is addressed to you (singular, informal), so adding ti is usually unnecessary.

• (Ti) zatvori prozor.

The pronoun ti can be added for emphasis, but normally it is omitted.

Here, prozor is the direct object of the verb zatvori, so it should be in the accusative case.

However, for many masculine inanimate nouns in Serbian, the accusative singular looks exactly the same as the nominative singular.

So:

• nominative: prozor = window
• accusative: prozor = window (same form)

That is why the sentence uses prozor.

Compare with a masculine animate noun, where the accusative usually changes:

• Vidim čovek-a. = I see the man.

But:

• Vidim prozor. = I see the window.

Jer means because.

It introduces a reason:

• Zatvori prozor, jer je sada hladno.
• Close the window, because it is cold now.

It is a very common conjunction in Serbian.

A close alternative is zato što:

• Zatvori prozor, zato što je sada hladno.

Both mean because, though jer is often shorter and very natural in everyday speech.

In standard Serbian writing, a comma is normally used before jer when it introduces an explanatory clause.

So:

• Zatvori prozor, jer je sada hladno.

This is standard punctuation.

Both are possible, but Serbian has a strong tendency for short unstressed words like je to appear in the second position of the clause. These are called clitics.

In the clause:

• jer je sada hladno

the conjunction jer comes first, and then the clitic je comes right after it.

That word order is very natural and standard.

You may also hear:

• jer je sad hladno

And in some contexts, speakers may use other word orders for emphasis, but jer je sada hladno is the most neutral here.

Because hladno here does not describe a noun directly. It is being used in an impersonal expression meaning:

• it is cold

Serbian often uses the neuter singular form in this kind of expression:

• Toplo je. = It is warm.
• Hladno je. = It is cold.
• Mračno je. = It is dark.

So hladno here is not agreeing with prozor. It is simply part of the expression je hladno.

Yes, in terms of meaning, English uses a dummy subject:

• it is cold

But Serbian usually does not need that dummy subject. It simply says:

• Hladno je. = It is cold.

So the second clause is literally more like:

• because is now cold

but naturally it means:

• because it is cold now

This is normal in Serbian.

Yes. Sada and sad both mean now.

• sada is the full form
• sad is a very common shorter form in everyday speech

So both are natural:

• jer je sada hladno
• jer je sad hladno

The meaning is the same.

This is about aspect, which is very important in Serbian.

• zatvoriti = perfective
• zatvarati = imperfective

The imperative zatvori comes from the perfective verb zatvoriti, and it usually means:

• do the action once
• complete it

So:

• Zatvori prozor. = Close the window.

This is the normal choice for a simple command to complete the action.

By contrast, zatvaraj (from zatvarati) can suggest repeated action, ongoing action, or a more process-focused idea, depending on context. It would not be the most neutral choice here.

Not perfectly. A very literal breakdown would be:

• Zatvori = close
• prozor = window
• jer = because
• je = is
• sada = now
• hladno = cold

So literally:

• Close window, because is now cold.

But natural English needs extra words:

• Close the window, because it is cold now.

This is a good example of how Serbian often leaves out things that English requires, such as the and the dummy subject it.

Yes, Serbian word order is fairly flexible, though some versions sound more neutral than others.

The original:

• Zatvori prozor, jer je sada hladno.

is a very natural, neutral sentence.

You could also say:

• Jer je sada hladno, zatvori prozor.

This is grammatically possible, but it sounds more marked because it puts the reason first.

So learners should treat the original version as the safest everyday pattern.

The easiest way is to change the imperative to the formal/plural form:

• Zatvorite prozor, jer je sada hladno.

That can mean:

• speaking politely to one person
• speaking to more than one person

If you want an even softer request, Serbian often uses forms like:

• Zatvorite prozor, molim vas. = Please close the window.
• Možete li da zatvorite prozor? = Can you close the window?