Omnes in bibliotheca tacent, ut magistram audire possint.

Omnes means all or everyone here. It is the nominative plural form, so it is functioning as the subject of tacent.

A learner might expect all people to be stated more explicitly, but Latin often leaves the noun understood. So omnes by itself can mean all of them or everyone.

In bibliotheca means in the library.

Here in is used with the ablative (bibliotheca) because it shows location: where something happens.

A useful contrast is:

• in bibliotheca = in the library / inside the library
• in bibliothecam = into the library / motion toward it

So the ablative is used because the sentence describes where they are being quiet, not movement into the library.

Tacent is present indicative active, 3rd person plural, from tacere.

It literally means:

• they are silent
• they keep quiet
• they are being quiet

Latin present tense often covers ideas that English may express in a few different ways, such as simple present or present progressive, depending on context.

Ut here means so that or in order that. It introduces a purpose clause.

So:

• ut magistram audire possint = so that they can hear the teacher

This tells us the purpose of the action in the main clause:

• Omnes in bibliotheca tacent = everyone is quiet in the library
• ut ... possint = so that ...

This is a very common Latin pattern: ut + subjunctive for purpose.

Because it is inside a purpose clause introduced by ut.

In Latin, purpose clauses normally use:

• ut = so that
• subjunctive verb

So possint is present subjunctive, from posse (to be able).

It does not necessarily mean doubt here. English speakers often first learn the subjunctive as something uncertain or hypothetical, but in Latin the subjunctive is also used in standard clause types like purpose clauses.

Possunt would be the indicative form: they are able or they can.

But after ut in a purpose clause, Latin uses the subjunctive, so we get possint instead.

Compare:

• possunt = indicative
• possint = subjunctive

So ut ... possint means so that they may be able to... or more naturally in English, so that they can...

Magistram is the direct object of audire.

The verb audire means to hear, and in Latin the thing or person heard goes into the accusative case.

So:

• magistra = teacher, subject form
• magistram = teacher, object form

Here, the people are hearing the teacher, so the accusative is required.

Audire is a present active infinitive, meaning to hear.

It depends on possint:

• possint audire = can hear / may be able to hear

This is a common construction in Latin, just as in English:

• they can hear
• they are able to hear

So audire completes the meaning of possint.

Because the whole phrase ut magistram audire possint is the subordinate clause expressing purpose.

Latin word order is often more flexible than English word order. The important thing is not position alone, but the grammar shown by endings and clause markers like ut.

The order here is perfectly natural:

• ut introduces the clause
• magistram is the object
• audire is the infinitive
• possint comes at the end

Latin often places the finite verb, especially in subordinate clauses, toward the end.

Because it refers back to omnes.

The subject of the main idea is all / everyone, and the implied subject of possint is the same group. Therefore the verb must be 3rd person plural.

So:

• omnes ... tacent
• omnes ... possint

Both verbs agree with the same plural subject.

In form, omnes could refer to either all people or all things, depending on context. But here the context clearly points to people, because:

• they are in a library
• they are being quiet
• they want to hear the teacher

So the natural understanding is everyone or all the people.

It is a purpose clause.

The clue is the meaning: everyone is quiet in order to hear the teacher.

A result clause would describe what actually happens as a result, often with clues like so ... that. But here the clause expresses intention or aim, not result.

So ut magistram audire possint answers the question:

• Why are they quiet?
• So that they can hear the teacher.

A very literal translation would be something like:

All are silent in the library, so that they may be able to hear the teacher.

That is useful for understanding the grammar, especially:

• ut = so that
• possint = subjunctive in a purpose clause
• audire = infinitive

But in natural English, you would usually say:

Everyone is quiet in the library so that they can hear the teacher.

So literal translation can help you learn the structure, but smoother English is usually better for final translation.