Mater fenestram claudit; ita infans quietius dormit.

Because fenestram is the direct object of claudit (closes). In Latin, the direct object usually goes in the accusative case.

• fenestra = window as a basic dictionary form, nominative singular
• fenestram = window as the thing being closed, accusative singular

So Mater fenestram claudit means Mother closes the window.

Because mater is the subject of the verb claudit. The subject is normally in the nominative case.

• mater = mother as the subject
• matrem would mean mother as a direct object

So here mater is the one doing the action.

Claudit means closes or is closing.

The ending -it tells you it is:

• third person singular
• present tense
• active voice

So claudit means he/she/it closes.

We know mother is the one doing it because:

1. mater is the subject in the nominative
2. claudit is singular, matching mater

Classical Latin normally has no articles like English the or a/an.

So:

• mater can mean mother, a mother, or the mother
• fenestram can mean a window or the window
• infans can mean an infant or the infant

You decide from the context which English article sounds natural.

Ita means thus, so, or in this way.

In this sentence, it connects the two ideas:

• Mother closes the window
• so / and so / thus the baby sleeps more quietly

It shows that the second part follows from the first.

Because quietius is the comparative adverb of quiete (quietly).

So:

• quiete = quietly
• quietius = more quietly

It describes how the baby sleeps, so it is an adverb, not an adjective.

Because quietius is an adverb, not an adjective.

Adjectives describe nouns and agree with them in gender, number, and case.
Adverbs describe verbs, adjectives, or other adverbs, and they do not agree with nouns.

Here quietius modifies dormit (sleeps), not infans.

So the meaning is:

• not the quieter baby
• but the baby sleeps more quietly

Infans is nominative singular, because it is the subject of dormit.

It looks the same as the dictionary form because many third-declension nouns have the same form in the nominative singular as the form listed in dictionaries.

So here:

• infans = the infant/baby as subject

Its accusative singular would usually be infantem.

Dormit means sleeps or is sleeping.

Like claudit, the ending -it shows:

• third person singular
• present tense
• active voice

It is singular because the subject is infans, which is one baby.

Latin word order is more flexible because the endings show the grammatical role of each word.

English depends much more on word order:

• Mother closes the window

Latin can often rearrange words without changing the basic meaning, because:

• mater is nominative = subject
• fenestram is accusative = object
• claudit is the verb

The sentence as given is quite natural Latin, but other orders could also work for emphasis.

Not really in the grammatical sense. It just helps the reader see the relationship between the two clauses.

The semicolon separates:

1. Mater fenestram claudit
2. ita infans quietius dormit

It shows a close connection: the first action leads to the second result.

Yes, in context that is a good way to understand it.

Depending on style, you could render the second clause as:

• so the baby sleeps more quietly
• thus the baby sleeps more quietly
• as a result, the baby sleeps more quietly

The exact English wording can vary, but the Latin idea is that the first action produces the second outcome.

Yes. Latin often uses an adverb with a verb just as English does.

• dormit = sleeps
• quietius = more quietly

So quietius dormit is a normal structure meaning sleeps more quietly.

Yes. Latin present tense can often be translated in different ways depending on context.

So:

• Mater fenestram claudit can mean Mother closes the window or Mother is closing the window
• infans quietius dormit can mean the baby sleeps more quietly or the baby is sleeping more quietly

English chooses between simple present and progressive more sharply than Latin does.

Because the verb ending already tells you the person and number.

Claudit already means he/she/it closes.
Since mater is present, Latin does not need to add a pronoun.

In fact, Latin often leaves out subject pronouns unless they are needed for emphasis or contrast.