Quies in bibliotheca discipulis grata est.

Quies is nominative singular, not plural.

This is a common point of confusion, because English speakers often expect a singular noun not to end in -es. But Latin nouns do not follow English-looking patterns. Quies is a third-declension noun, and its dictionary form is:

• quies, quietis (f.) = rest, quiet, peace

In this sentence, quies is the subject because:

• it is in the nominative
• the verb is est = is (singular)
• the adjective grata is also singular and agrees with it

So quies means quiet/rest as one singular idea.

Because grata agrees with quies, and quies is a feminine noun.

In Latin, adjectives agree with the noun they describe in:

• gender
• number
• case

So here:

• quies = nominative singular feminine
• grata = nominative singular feminine

That is why Latin uses grata, not gratus or gratum.

Here grata est means something like:

• is pleasing
• is welcome
• is agreeable
• is dear

A learner may first think of English grateful, but that is not what is happening here.

In Latin, gratus, grata, gratum can describe something that is pleasing to someone. So:

• quies ... discipulis grata est = quiet ... is pleasing/welcome to the students

So quies is not feeling gratitude. Instead, quies is the thing that the students find pleasant.

Because gratus often takes the dative of the person who finds something pleasing.

So the pattern is:

• something
  • dative person
    • gratus/grata/gratum est

That means:

• something is pleasing/welcome to someone

Here:

• quies = the thing that is pleasing
• discipulis = to the students

So discipulis is a dative plural.

In form, yes: discipulis can be either dative plural or ablative plural.

But in this sentence it is understood as dative, because the construction with grata est strongly points that way.

Latin often has forms that could belong to more than one case. You decide by the sentence structure and meaning. Here:

• grata est naturally goes with a dative of the person affected
• so discipulis = to the students

An ablative reading would not fit nearly as well.

Because in takes different cases depending on whether there is:

• location = in + ablative
• motion toward = in + accusative

Here the sentence describes where the quiet is:

• in bibliotheca = in the library

There is no movement into the library, so Latin uses the ablative.

Compare:

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

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

So a Latin noun like bibliotheca can mean:

• library
• a library
• the library

You decide from context which English wording is best.

The same is true for discipulis:

• to students
• to the students

and for quies:

• quiet
• the quiet

Latin simply does not mark that distinction with a separate word.

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

A very literal breakdown is:

• Quies = quiet/rest
• in bibliotheca = in the library
• discipulis = to the students
• grata est = is pleasing/welcome

So the whole sentence is roughly:

• Quiet in the library is pleasing to the students

The order used here is natural Latin, but other orders are possible. For example, Latin can move words around for emphasis.

Putting quies first gives it prominence. Putting est at the end is also very common in Latin.

It is a prepositional phrase of place, telling you where the quiet is.

It modifies quies in sense:

• the quiet in the library

So it is not the subject and not the indirect object. It simply adds location.

The basic structure is:

• quies = subject
• in bibliotheca = where
• discipulis = to whom it is pleasing
• grata est = predicate adjective + verb

The main dictionary forms are:

• quies, quietis (f.) = rest, quiet, peace
• bibliotheca, bibliothecae (f.) = library
• discipulus, discipuli (m.) = student
• gratus, grata, gratum = pleasing, welcome, dear
• sum, esse = to be

Knowing the dictionary form helps you recognize what each inflected form is doing:

• quies comes from quies, quietis
• bibliotheca here is ablative singular after in
• discipulis is dative plural
• grata agrees with quies
• est is third-person singular of sum

Yes. Depending on context, quies can mean:

• rest
• quiet
• peace
• stillness
• repose

So the exact English translation can vary. In this sentence, because of in bibliotheca, quiet is probably the most natural choice. But the Latin word itself is broader than one single English word.