Ne menj a könyvtárba, mert ma nincs nyitva.

Because ne is used to negate a command, request, or prohibition.

• Ne menj... = Don’t go...
• Nem mész... = You are not going... / You don’t go...

So:

• nem negates a statement
• ne negates an imperative or subjunctive form

That is why Ne menj a könyvtárba is correct for Don’t go to the library.

Menj is the imperative form of the verb menni (to go) for te (you, singular informal).

Compare:

• mész = you go / you are going
• menj = go!

So:

• Mész a könyvtárba. = You’re going to the library.
• Ne menj a könyvtárba. = Don’t go to the library.

This verb is a little irregular, so learners usually just have to memorize that the imperative of menni is menj.

Yes. Ne menj is addressed to one person in the informal singular.

Other versions would be:

• Ne menjetek a könyvtárba... = Don’t go... (to several people, informal)
• Ne menjen a könyvtárba... = Don’t go... (to one person, formal)
• Ne menjenek a könyvtárba... = Don’t go... (to several people, formal)

So the original sentence sounds like you are speaking casually to one person.

Könyvtárba is made up of:

• könyvtár = library
• -ba = into / to inside

So a könyvtárba literally means into the library.

With places like buildings, Hungarian often uses the illative ending -ba/-be when the idea is going into that place.

Compare:

• könyvtárban = in the library
• könyvtárba = into / to the library

So after a verb like menni (to go), könyvtárba is exactly what you would expect.

A is the definite article, meaning the.

So:

• a könyvtárba = to the library

Hungarian often uses the definite article in places where English sometimes feels a little freer about using the. In this sentence, it refers to a specific, contextually known library, or simply the library that both speaker and listener understand.

Because in Hungarian the article comes before the noun, just like the in English:

• a könyvtár = the library

Then the case ending attaches to the noun:

• a könyvtárba = to the library

The article does not take the ending; the noun does.

So the structure is:

• a
  • könyvtár
    • -ba

not the other way around.

Mert means because.

It introduces the reason:

• Ne menj a könyvtárba = Don’t go to the library
• mert ma nincs nyitva = because it isn’t open today

So the whole sentence means:

• Don’t go to the library, because it isn’t open today.

This is a very common and straightforward way to give a reason in Hungarian.

Hungarian commonly expresses this idea with:

• nyitva van = is open
• nincs nyitva = is not open

Here:

• nyitva is a form meaning something like in an open state
• nincs is is not / there is not

So ma nincs nyitva literally feels like:

• today it is not in an open state

This is the normal Hungarian way to talk about whether a shop, library, office, etc. is open.

In the 3rd person singular present tense, the negative of van is nincs.

So:

• van = is
• nincs = is not

Examples:

• A bolt nyitva van. = The shop is open.
• A bolt nincs nyitva. = The shop isn’t open.

So nem van is not the normal standard form here. Hungarian uses nincs instead.

The subject is understood from context: it is the library.

Hungarian often leaves out subjects when they are already clear. So after saying a könyvtárba, the next clause naturally refers back to the library:

• mert ma nincs nyitva = because today it isn’t open

English usually needs it, but Hungarian often does not.

Ma means today, and its position helps set the time frame for the clause.

• ma nincs nyitva = it isn’t open today

This is a very natural word order. Hungarian word order is flexible, but it is not random: it often reflects topic and emphasis.

Here, ma works well as the time setting for the reason clause.

You may also hear:

• nincs ma nyitva

That is also possible, but the emphasis can feel slightly different. The original ma nincs nyitva is very natural and neutral.

Yes. For example:

• Ma ne menj a könyvtárba, mert nincs nyitva.

This means roughly:

• Don’t go to the library today, because it isn’t open.

That version puts today more strongly with the command itself. The original sentence puts today in the explanation:

• Don’t go to the library, because today it isn’t open.

Both are possible; the difference is mostly about emphasis and information structure.

No, not in standard Hungarian.

To say Don’t go, you need:

• Ne menj

not

• Nem menj

This is one of the most important patterns to learn:

• Menj! = Go!
• Ne menj! = Don’t go!

So the sentence must begin with Ne menj...

Usually, no.

For opening hours and whether a place is open for business, Hungarian normally uses:

• nyitva van
• nincs nyitva

Using nyitott here would sound unnatural or would suggest a different nuance.

Very roughly:

• nyitva = open in the practical/state sense
• nyitott = often more like opened or an adjective with other meanings, depending on context

So for a library, store, office, restaurant, etc., the standard phrase is nyitva van / nincs nyitva.

Yes, in standard Hungarian spelling, a clause introduced by mert is separated with a comma.

So:

• Ne menj a könyvtárba, mert ma nincs nyitva.

That comma works much like the comma often used before because when separating clauses in Hungarian punctuation.

A fairly literal breakdown is:

• Ne = don’t
• menj = go
• a könyvtárba = to/into the library
• mert = because
• ma = today
• nincs nyitva = is not open

So the sentence is essentially:

• Don’t go to the library, because today it is not open.

That literal structure is very close to the natural English meaning, which makes this sentence a nice example of everyday Hungarian grammar.