Mater gaudet, quia infans heri nocte sanus natus est.

Mater is nominative singular. It is the subject of gaudet, so it appears in the nominative case.

• mater = mother
• gaudet = rejoices / is glad

So mater gaudet means the mother is glad.

Gaudet is:

• 3rd person singular
• present tense
• active voice
• from the verb gaudeo, gaudere = to rejoice, be glad

It agrees with mater, which is a singular subject.

So:

• gaudeo = I am glad
• gaudes = you are glad
• gaudet = he/she is glad

Quia means because. It introduces the reason why the mother is glad.

So the sentence is divided like this:

• Mater gaudet = The mother is glad
• quia infans heri nocte sanus natus est = because the baby was born healthy last night

This is a very common way to introduce a cause or explanation in Latin.

Infans is nominative singular, because it is the subject of natus est.

It means infant, baby, or sometimes child. In this sentence, baby is the most natural translation.

A useful thing to notice is that infans is a 3rd-declension noun. Its nominative singular ends in -s, but that does not mean it is plural.

Latin does not have definite or indefinite articles like English the, a, or an.

So:

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

You choose the most natural English wording from the context. In this sentence, the mother and the baby are the most natural translations.

This is a normal Latin way to express time.

• heri = yesterday
• nocte = at night / in the night (ablative of time)

Together, heri nocte means last night or more literally yesterday at night.

English uses one expression, last night, but Latin often builds that idea out of separate words.

Nocte is an ablative of time when. Latin often uses the ablative without a preposition to show when something happened.

Examples:

• eo die = on that day
• prima luce = at dawn
• nocte = at night
• heri nocte = last night

So nocte does not need a word like in or on.

This is because natus est is the normal perfect form of the verb nascor = to be born.

• natus = born (perfect participle)
• est = is

Together, natus est literally looks like has been born, but in normal English it is usually just was born.

Then sanus adds extra information about the baby:

• sanus = healthy
• natus est = was born

So sanus natus est means was born healthy.

That is a very common beginner question. In this construction, est is part of a compound perfect tense.

The verb nascor is a deponent verb, which means it has passive-looking forms but an active meaning. Its perfect system is built with:

• a perfect participle: natus
• a form of sum: est

So natus est does not mean is born here. It means was born or has been born, depending on context.

This is just how the perfect tense of nascor works.

Both sanus and natus agree with infans in:

• case: nominative
• number: singular
• gender: masculine here

So the sentence is referring to a male baby, because the adjectives/participle are masculine:

• sanus
• natus

If the baby were female, Latin would say:

• Mater gaudet, quia infans heri nocte sana nata est.

So even though infans itself does not change form here, the agreeing words show the baby’s sex.

Because infans is a noun that can refer to either sex, but the adjective and participle must show which sex is meant in context.

Here:

• sanus = masculine
• natus = masculine

So the infant is understood to be male.

If the infant were female, Latin would use:

• sana
• nata

This is a very important feature of Latin: even when the noun itself is not obviously masculine or feminine in form, agreement can still make the meaning clear.

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

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

• Mater gaudet, quia infans sanus heri nocte natus est.
• Quia infans heri nocte sanus natus est, mater gaudet.

The original order is perfectly natural, but Latin often moves words around for:

• emphasis
• style
• rhythm

English depends much more on word order to show meaning, but Latin depends more on endings.

Because sanus describes the state in which the baby was born: healthy.

Latin often places an adjective before a participle or verb in a way that feels very natural:

• sanus natus est = was born healthy

This does not mean sanus is directly modifying mater or some other noun. It goes with infans and tells us something about the infant at the moment of birth.

So the sense is:

• the baby was born
• and the baby was healthy

Yes. For example, Latin could say laeta est if the mother is female and you want the idea is happy rather than rejoices.

But gaudet is a very good choice because it expresses active joy or rejoicing, especially for a reason introduced by quia.

Compare:

• mater gaudet = the mother rejoices / is glad
• mater laeta est = the mother is happy

Both are possible, but gaudet fits very naturally with because the baby was born healthy last night.