Hac nocte infans sanus natus est.

This is a very common Latin construction: the ablative of time when.

A specific point in time is often expressed with the ablative alone, without a preposition:

• hac nocte = on this night / that night
• eo die = on that day
• tertia hora = at the third hour

So in is not needed here. A learner coming from English often expects a preposition, but Latin regularly leaves it out in time expressions like this.

Because hac has to agree with nocte.

Nox, noctis is a feminine noun, and here nocte is ablative singular. The demonstrative hic, haec, hoc must match that case, number, and gender.

So:

• nominative feminine singular: haec
• ablative feminine singular: hac

Since the sentence has nocte in the ablative singular, the correct form is hac.

Infans is nominative singular, and it is the subject of the sentence.

The basic structure is:

• hac nocte = time expression
• infans = subject
• sanus = adjective describing the subject
• natus est = verb

So infans is the one who was born.

Because both words agree with infans.

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

• gender
• number
• case

Here:

• infans is nominative singular
• sanus is nominative singular masculine
• natus is nominative singular masculine

That means the infant is understood as male, or at least is being referred to with masculine agreement.

If the infant were female, you would expect:

• infans sana nata est

Even though infans itself can refer to either a male or female child, the agreeing adjective and participle tell you which gender is meant in this sentence.

Natus est is the perfect indicative of the verb nascor, nasci, natus sum, meaning to be born.

This verb is deponent, which means it uses passive-looking forms but has an active meaning.

So although natus est looks like:

• participle + est

and with a normal verb that often signals a perfect passive, here it is simply the normal perfect form of a deponent verb.

So natus est means:

• was born
• or has been born

In most contexts, English will naturally translate it as was born.

Because nascor is a deponent verb.

Deponent verbs are a special group in Latin:

• they have passive forms
• but active meanings

So:

• nascitur = is born / is being born
• natus est = was born / has been born

This is something learners simply have to get used to. It is not a mistake, and it is not an exception just in this sentence. It is how the verb nascor normally works.

It can suggest either, and in English both are natural ways to understand it.

Latin often allows an adjective like this to feel either:

• attributive: a healthy infant
• or predicative: the infant was born healthy

With natus est, English often prefers the predicative idea:

• the infant was born healthy

But depending on context, a healthy infant was born that night can also be a perfectly reasonable translation.

Latin does not use articles like a and the, so context usually does the work that English articles do.

Because Classical Latin has no articles.

So infans can mean:

• an infant
• the infant
• sometimes just infant in a more general sense

Which one is best depends on context.

That is why a single Latin sentence can often be translated into English in more than one perfectly good way.

Because Latin word order is much more flexible than English word order.

A very common Latin pattern is:

• put important setting information early
• put the finite verb at the end

So this sentence feels very natural:

• Hac nocte = setting in time first
• infans sanus = subject and description
• natus est = verb at the end

English relies heavily on word order to show grammar, but Latin relies much more on endings. That gives Latin freedom to move words around for emphasis or style.

Yes, to a degree.

For example, these would still express essentially the same basic idea:

• Infans sanus hac nocte natus est
• Sanus infans hac nocte natus est
• Infans hac nocte sanus natus est

Because the endings show what each word is doing, the meaning does not collapse when the order changes.

However, the different orders can change the emphasis:

• starting with hac nocte highlights the time
• putting sanus early can highlight the infant's condition
• keeping natus est at the end gives a very typical Latin cadence

So the original order is not random, even though other orders are possible.