Magistra in bibliotheca loquens a discipulis auditur.

Because the verb is passive, not active.

• audit = he/she hears
• auditur = he/she is heard

In this sentence, magistra is the one being heard, so Latin uses the passive form auditur.

Grammatically, auditur is:

• 3rd person singular
• present tense
• passive indicative

So it means is heard.

Because magistra is the subject of the sentence.

Even though the teacher is not doing the action of hearing, she is still the grammatical subject because the verb is passive:

• active: discipuli magistram audiunt = the students hear the teacher
• passive: magistra a discipulis auditur = the teacher is heard by the students

In a passive sentence, the person or thing receiving the action becomes the subject, so magistra is nominative.

a discipulis means by the students.

In Latin, the agent of a passive verb is commonly expressed with:

• a or ab
  • ablative

So here:

• a = by
• discipulis = ablative plural of discipulus

This construction is used especially for a personal agent, someone actually performing the action.

So:

• magistra a discipulis auditur = the teacher is heard by the students

Because with a personal agent in a passive sentence, Latin normally uses a/ab + ablative.

So if you want to say by the students, you usually say:

• a discipulis

If Latin omits a/ab, the ablative often has a different sense, especially with things rather than people, such as means or instrument.

Compare:

• a discipulis = by the students
• gladio vulneratur = he is wounded with a sword

The first is a personal doer of the action; the second is an instrument.

Loquens is a present participle meaning speaking.

It describes magistra, so the sentence is essentially saying:

• the teacher, speaking in the library, is heard by the students
• or the teacher who is speaking in the library is heard by the students

A participle is a verbal adjective, so it behaves partly like a verb and partly like an adjective:

• it comes from a verb
• but it agrees with a noun

Here loquens agrees with magistra.

Because it agrees with magistra in number, case, and gender.

• magistra is singular, nominative, feminine
• loquens here is singular nominative and refers to that noun

Even though the participle form loquens looks the same for masculine and feminine in the nominative singular, the context shows it modifies magistra, not discipulis.

Also, discipulis is ablative plural, so it cannot match loquens here.

Because loquor is a deponent verb.

Deponent verbs:

• have passive-looking forms
• but active meanings

So:

• loquor means I speak, not I am spoken
• loquens means speaking

This is very common in Latin. Deponent verbs often confuse English speakers at first because their forms look passive, but their meaning is active.

Loquens is a present participle, so it usually expresses action happening at the same time as the main verb.

Here the main verb is auditur = is heard.

So the idea is:

• the teacher is speaking
• and at that same time, she is being heard by the students

That is why loquens is naturally understood as speaking or while speaking.

Because in with the ablative usually means in or inside, showing location.

• in bibliotheca = in the library

If Latin wanted to show motion into the library, it would normally use in + accusative:

• in bibliothecam = into the library

So the contrast is:

• in bibliotheca = location
• in bibliothecam = motion toward/into

Latin word order is much more flexible than English word order because the endings show the grammatical relationships.

So this sentence could be rearranged in various ways without changing the basic meaning, for example:

• Magistra in bibliotheca loquens a discipulis auditur
• A discipulis magistra in bibliotheca loquens auditur
• In bibliotheca magistra loquens a discipulis auditur

The exact order can affect emphasis or style, but the case endings still tell you:

• magistra = subject
• a discipulis = agent
• in bibliotheca = location
• loquens = describing magistra

Yes, very nearly.

Latin often uses a participle where English might use:

• who is speaking
• while speaking

So:

• magistra loquens ≈ the teacher who is speaking
• or the teacher, speaking

A fuller version with a relative clause would be:

• magistra quae in bibliotheca loquitur a discipulis auditur

That is grammatically fine, but the participle version is more compact.

In form, discipulis could be either dative plural or ablative plural, because many 2nd-declension plural endings look the same.

But here it must be ablative because it follows a, and a/ab takes the ablative.

So in this sentence:

• discipulis = ablative plural

Because Latin can express that idea with a participle instead of a relative clause.

English often says:

• the teacher who is speaking

Latin can compress that to:

• magistra loquens

So Latin does not need a separate who is here. The participle itself carries that descriptive sense.

You would look it up under the verb loquor, loqui, locutus sum.

That is the dictionary entry for to speak.

From that verb:

• loquor = I speak
• loquens = speaking

This is useful because participles are normally found by identifying the verb they come from.

Yes. Both are reasonable English ways to reflect the Latin structure.

Latin participles can be translated in more than one natural way:

• as an adjective-like phrase: the speaking teacher
• as a relative clause: the teacher who is speaking
• as a participial phrase: the teacher, speaking...

In this sentence, the most natural English is usually:

• The teacher, speaking in the library, is heard by the students or
• The teacher who is speaking in the library is heard by the students

The Latin grammar allows that flexibility.