Puer domi manere cogitur, quia ventus frigidus est et nox iam venit.

Puer is nominative singular, because it is the subject of cogitur. In other words, the boy is the one being forced.

It is a second-declension masculine noun, but unlike many second-declension nouns, it keeps the -er in the nominative: puer, pueri.

Domi means at home. It is a special old case called the locative, which survives in a small number of words in Latin.

With domus, Latin often distinguishes these meanings:

• domi = at home
• domum = to home / homeward
• domo = from home

So puer domi manere means the boy to stay at home, not motion toward or away from home.

You can also find in domo, but that more literally means in the house and can emphasize location inside the building rather than the idiomatic idea at home.

Because it depends on cogitur.

The verb cogo, cogere means to force or compel. In Latin, verbs like this are often followed by an infinitive to show what someone is forced to do.

So:

• cogitur = he is forced
• manere = to remain / to stay

Together: cogitur manere = he is forced to stay

Because Latin infinitives do not use a separate word like English to.

In English, we say to stay. In Latin, the infinitive is just one form: manere.

So manere already means to stay all by itself.

Cogitur is the passive form of cogit.

• cogit = he forces
• cogitur = he is forced

The sentence focuses on what happens to the boy, not on who is forcing him. Latin often uses the passive when the agent is unknown, obvious, or unimportant.

If Latin wanted to say who is forcing him, it could add an agent with ab + ablative, for example:

• a matre cogitur = he is forced by his mother

Because the sentence does not need to.

Latin often leaves out the agent in a passive sentence when the context already makes the situation clear or when the specific agent is not important. The important idea here is simply that the boy must stay home.

English does this too: He is being kept at home does not have to say by whom.

Quia means because and introduces a reason.

So the structure is:

• main clause: Puer domi manere cogitur
• reason clause: quia ventus frigidus est et nox iam venit

Latin also has other words for because, such as quod and quoniam, but quia is a very common and straightforward choice.

Because the sentence presents these reasons as facts:

• the wind is cold
• night has already come / night is already coming

After quia, Latin often uses the indicative when the speaker treats the reason as real and factual.

Without macrons, venit can be ambiguous.

It can represent:

• venit = present tense, he/she/it comes
• vēnit = perfect tense, he/she/it came / has come

In this sentence, because of iam (already) and the subject nox (night), the perfect sense is very likely: night has already come or more naturally night has already fallen.

If macrons were written, the perfect would be vēnit.

Because it agrees with ventus.

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

• gender
• number
• case

Here:

• ventus = masculine, singular, nominative
• frigidus = masculine, singular, nominative

So ventus frigidus means the cold wind or the wind is cold.

Because Latin word order is flexible, and adjectives can come either before or after the noun.

Both noun-adjective and adjective-noun orders are possible in Latin. The choice often depends on style, emphasis, or habit rather than strict grammar.

So ventus frigidus is completely normal Latin.

Iam is an adverb meaning already / now by this time. Latin often places adverbs near the word they modify, so iam venit naturally means has already come or is already coming.

Its position also gives a smooth emphasis: the coming of night is not just happening, it has happened already.

Yes.

After et, the sentence gives another coordinated statement:

• ventus frigidus est
• nox iam venit

Each part has its own subject and verb:

• ventus → est
• nox → venit

So nox is the subject of the second clause.

Because Latin has no articles.

Latin does not have separate words for the or a/an. Whether a noun is definite or indefinite is understood from context.

So puer could mean the boy or a boy, depending on the situation. The same is true for ventus and nox.