Discipulae in bibliotheca tacent, quia magistra earum legit.

Because discipulae is being used as a nominative plural subject here: the female students or the schoolgirls.

The form discipulae can be ambiguous in isolation, because it can also be genitive singular or dative singular. But the verb tacent is plural, so that tells you discipulae must be the plural subject.

Latin verbs change their endings to match the subject.

• tacet = she/he/it is silent
• tacent = they are silent

Since discipulae is plural, the verb must also be plural: tacent.

Because in takes different cases depending on meaning:

• in + ablative = in/on/at a place, with no movement
• in + accusative = into a place, showing motion toward it

So:

• in bibliotheca = in the library
• in bibliothecam = into the library

Here the students are already there, so Latin uses the ablative: bibliotheca.

Quia means because. It introduces a clause that gives the reason for what happens in the main clause.

So the structure is:

• Discipulae in bibliotheca tacent = main statement
• quia magistra earum legit = reason

In other words: they are silent because their teacher is reading.

Magistra is in the nominative singular, which is the normal case for the subject of a clause. The verb legit is also singular, so they fit together:

• magistra = the teacher
• legit = reads

So magistra legit means the teacher reads.

Earum means of them or their. It is genitive plural feminine.

It refers back to discipulae, so it means their in the sense the girls' or the female students'.

In magistra earum:

• magistra = teacher
• earum = of them / their

So literally it is the teacher of them, which English naturally says as their teacher.

Because suus, sua, suum is a reflexive possessive. It normally refers back to the subject of its own clause.

In the clause quia magistra earum legit, the subject is magistra. So if Latin said magistra sua, it would mean something like her own teacher—that is, the teacher belonging to the teacher, which is not the intended meaning.

But the possessor here is discipulae, the subject of the main clause, not the subject of the quia clause. So Latin uses earum, not sua.

Yes. In ordinary spelling, legit can be either:

• present: reads
• perfect: read / has read

Usually context tells you which one is meant. Here reads makes the best sense, because it explains why the students are silent at the same time.

If vowel length is marked, the perfect form is written lēgit, which helps distinguish it.

Latin word order is fairly flexible, because the endings show how words function.

This sentence uses a very natural order, but other arrangements are possible, for example:

• In bibliotheca discipulae tacent
• Quia earum magistra legit, discipulae in bibliotheca tacent

The meaning stays basically the same, though the emphasis can change. Latin often likes to put the verb near the end, as in tacent and legit here.

Because Latin has no definite article and no indefinite article. It does not have exact equivalents of the or a/an.

So:

• discipulae can mean students, the students, or sometimes some students
• magistra can mean teacher, the teacher, or a teacher

English has to choose an article when translating, but Latin does not. Context tells you what is most natural.