V knihovně je také pravidlo, že se nesmí mluvit nahlas.

Because knihovně is the locative case, which you need after v when you are talking about being in a place (no movement).

• The noun knihovna (library) is feminine.
• Its singular forms are roughly:
  • Nominative: knihovna (the basic “dictionary” form)
  • Genitive: knihovny
  • Dative: knihovně
  • Accusative: knihovnu
  • Locative: knihovně
  • Instrumental: knihovnou

After v:

• Use accusative when there is motion into something:
  
  • Jdu do knihovny. – I’m going to the library.
  • Dám to do knihovny. – I’ll put it into the library.
• Use locative when it’s about being in a place:
  
  • Jsem v knihovně. – I’m in the library.

So v knihovně = “in the library,” with knihovně in the locative case.

The core structure is:

• je pravidlo – “there is a rule”

Then také means “also / as well”, so:

• V knihovně je také pravidlo…
  = “In the library there is also a rule…”

It implies there are probably other rules, and this is one of them.

Other possible positions of také and their feel:

• V knihovně je také jedno pravidlo… – there is also one (particular) rule.
• V knihovně také je pravidlo, že… – grammatically possible but less neutral; the stress falls a bit more on je (“there really is a rule”).
• Také v knihovně je pravidlo, že… – “Also in the library there is a rule that…”, emphasizing the library compared to other places.

The given sentence, V knihovně je také pravidlo, že…, is the most neutral and typical word order.

Že introduces a subordinate clause (“that”-clause) which explains the content of the rule.

• pravidlo – rule
• že se nesmí mluvit nahlas – that one must not speak loudly

So the structure is exactly parallel to English:

• je pravidlo, že… = “there is a rule that…”

In Czech this že-clause is very common after nouns like:

• pravidlo, že… – a rule that…
• fakt, že… – the fact that…
• zpráva, že… – the news that…

Without že the sentence would be ungrammatical; you can’t directly say pravidlo se nesmí mluvit nahlas.

Here se creates an impersonal / general construction:

• (něco) se nesmí + infinitive ≈ “one must not … / people are not allowed to …”

So:

• se nesmí mluvit nahlas ≈ “it is not allowed to speak loudly” / “you are not allowed to speak loudly.”

Nobody is explicitly named as the subject (like “people,” “you,” “we”); the sentence just states a general rule. This impersonal construction with se is very common in Czech:

• Tady se nekouří. – No smoking here. (Lit. “Here one doesn’t smoke.”)
• Na ulici se nesmí pít alkohol. – You’re not allowed to drink alcohol on the street.

So se helps make the statement general and rule-like, without a specific subject.

Nesmí comes from the verb smět = “to be allowed (to do something).”

Conjugation (present tense):

• já smím
• ty smíš
• on/ona/ono smí
• my smíme
• vy smíte
• oni smějí / smí

In the sentence we have:

• se nesmí mluvit – literally “(it) is not allowed to speak.”

This is 3rd person singular (smí) used impersonally, with se, to express a general prohibition.

Contrast:

• nemůže – from moci = “can / be able to.” This expresses ability, not permission.
  • Nemůžu mluvit nahlas. – I can’t speak loudly (maybe because I lost my voice).
  • Nesmím mluvit nahlas. – I’m not allowed to speak loudly (rule).
• nesmíte mluvit nahlas. – “You (plural/formal) are not allowed to speak loudly.”
  • This addresses the listener directly.
  • The original se nesmí mluvit nahlas is more general, like a sign or regulation.

In the pattern (se) nesmí + infinitive, the infinitive is required:

• se nesmí mluvit – may not speak
• se nesmí jíst – may not eat
• se nesmí fotit – may not take photos

Smět functions a bit like English “may / be allowed to”:

• Smím mluvit? – May I speak?
• Nesmíš kouřit. – You’re not allowed to smoke.

When you have this impersonal construction se nesmí, you always follow it with the infinitive: mluvit, kouřit, jíst, etc.

You could also see a variant word order:

• že se nahlas nesmí mluvit – just a different emphasis, same meaning.

Both mean “to speak loudly” and are correct; the nuance is small:

• mluvit nahlas
  • Very common, everyday phrase.
  • Literally “to speak out loud.”
• mluvit hlasitě
  • Uses the adverb hlasitě = “loudly.”
  • Slightly more descriptive or neutral in style.

In a rule or sign, mluvit nahlas sounds completely natural and probably a bit more common:

• V knihovně se nesmí mluvit nahlas.
• V knihovně se nesmí mluvit hlasitě. (also fine)

Czech has no articles (“a/an/the”), so v knihovně can be translated as either:

• in the library
• in a library

The exact English translation depends on context:

• If you are talking about your usual local library, English would choose “in the library.”
• If you mean some library in general, English might use “in a library.”

To make it explicitly “this / that library”, Czech can add a demonstrative:

• V té knihovně je také pravidlo… – “In that (particular) library, there is also a rule…”

But in many contexts v knihovně is naturally understood as “in the library” without needing a special word for “the.”

Yes, that is correct Czech:

• V knihovně je pravidlo, že nesmíte mluvit nahlas.

The difference is in who is being addressed and how explicit it is:

1. Original sentence – že se nesmí mluvit nahlas

   • General rule, impersonal:
   • “that one must not speak loudly / that it is not allowed to speak loudly.”
   • Sounds like neutral rule text or a sign.

2. Alternative – že nesmíte mluvit nahlas

   • Directly addresses “you” (plural or formal singular).
   • “that you are not allowed to speak loudly.”
   • Sounds more like someone talking directly to visitors or readers.

Both are grammatical; the original is more impersonal and typical for describing rules in general terms.

Phonetically, it’s a bit tricky for English speakers because of v kn together:

• v – usually [v], but in fast speech it can weaken or almost disappear.
• knihovně – roughly [k-nih-ov-nye]
  
  • kn like “knee,” but pronounced with both consonants separately: k
    • n.
  • ň is a palatal “ny” sound, like Spanish ñ in señor.

So you get something like:

• v knihovně ≈ [fk-nih-ov-nye] in fast speech
  (the v often blends with k, almost like fk.)

Practice slowly:

1. knihovna – kni-hov-na
2. knihovně – kni-hov-ně
3. Add the v: v knihovně – v-kni-hov-ně

Over time, your tongue will get used to hitting v then k in quick succession.