Magistra hodie severior est quam heri, quia discipuli in bibliotheca non tacent.

Magistra is nominative singular, because it is the subject of the sentence: the teacher.

Its dictionary form is magistra, magistrae and it is a first-declension feminine noun. Here it means the teacher is the one being described as stricter today.

Severior is the comparative form of severa/severus, meaning stricter or more strict.

So:

• severa est = she is strict
• severior est = she is stricter

Because the sentence compares today with yesterday, Latin needs the comparative form.

Latin often includes the verb est = is, especially in straightforward statements.

So:

• Magistra severior est = The teacher is stricter

Sometimes Latin can leave out est if it is easily understood, but here it is clearly expressed.

Quam means than in comparisons.

So:

• severior quam heri = stricter than yesterday

This is the normal way Latin forms this kind of comparison:

• comparative adjective + quam

For example:

• maior quam = bigger than
• celerior quam = faster than

Heri is an adverb meaning yesterday. It does not change its form.

So quam heri literally means than yesterday, but in natural English we usually understand it as than she was yesterday.

Latin often uses a simple time adverb like this where English mentally supplies the rest.

Hodie is an adverb meaning today.

It tells when the teacher is stricter:

• Magistra hodie severior est = The teacher today is stricter / The teacher is stricter today

Like heri, it is an adverb and does not change its ending.

Discipuli is nominative plural, meaning the students or the pupils.

It is the subject of the second clause:

• discipuli ... non tacent = the students are not silent / the students are not keeping quiet

The verb tacent is plural, so it matches discipuli.

Quia means because.

It introduces the reason:

• quia discipuli in bibliotheca non tacent = because the students are not being quiet in the library

So the whole sentence gives a cause:

• the teacher is stricter today
• because the students are not quiet

Tacent is the third person plural present active indicative of tacere, meaning to be silent, to keep quiet, or to be quiet.

It is plural because the subject is discipuli:

• discipulus tacet = the student is quiet
• discipuli tacent = the students are quiet

With non, it becomes:

• discipuli non tacent = the students are not quiet

Non is the normal Latin word for not, and it usually goes directly before the word it negates, especially before the verb.

So:

• non tacent = are not quiet

That is the most natural placement here.

With in, Latin uses different cases depending on the meaning:

• in + ablative = in / on a place, showing location
• in + accusative = into / onto a place, showing motion toward

Here the students are in the library, not going into the library, so Latin uses the ablative:

• in bibliotheca = in the library

If they were moving into it, you would expect:

• in bibliothecam

It is ablative singular, because it follows in in a location expression.

The noun is bibliotheca, bibliothecae, a first-declension noun meaning library.

So:

• in bibliotheca = in the library

Because the verb tacent already carries the meaning are quiet / keep quiet / are silent.

Latin often uses one verb where English might use a longer expression.

So discipuli non tacent can be translated in several natural ways:

• the students are not quiet
• the students are not keeping quiet
• the students are being noisy

The exact English wording depends on style, but the Latin verb itself is simple.

Latin word order is more flexible than English word order, because endings show the grammar.

This sentence is arranged quite naturally:

• Magistra — subject first
• hodie — time word
• severior est — main statement
• quam heri — comparison
• quia ... — reason clause

A Latin author could move some of these words around for emphasis, but the basic meaning would stay the same because the forms still show their roles.

In theory, discipuli could have more than one grammatical possibility when seen alone, because Latin endings can overlap. But in this sentence it is clearly nominative plural.

Why?

Because:

• it matches the plural verb tacent
• it makes sense as the subject of the clause

So here discipuli definitely means the students.

Latin does not have articles like English the and a/an.

So:

• magistra can mean teacher or the teacher
• discipuli can mean students or the students
• bibliotheca can mean library or the library

English has to choose an article when translating, but Latin does not mark that distinction directly.

Here quia introduces a straightforward factual reason, so Latin uses the indicative:

• tacent is indicative

That is the normal pattern for a simple because clause:

• quia + indicative

At an elementary level, it is enough to recognize that quia commonly introduces an ordinary reason clause with a regular finite verb.