Nescio cur frater tam sero surgat; soror enim ad scholam prima venire solet.

Because cur frater tam sero surgat is an indirect question after nescio (I do not know).

In Latin, indirect questions normally use the subjunctive, even when English uses an ordinary indicative verb:

• Cur surgit? = Why is he getting up? / Why does he get up?
• Nescio cur surgat. = I do not know why he is getting up / gets up.

So surgat does not mean may get up here. It is simply the normal mood for an indirect question.

Cur means why.

It introduces the indirect question:

• Nescio cur... = I do not know why...

This is very common in Latin. Other question words can work the same way in indirect questions, such as quis (who), quid (what), ubi (where), and so on.

The subject is frater (brother).

So the clause breaks down like this:

• frater = the brother
• tam sero = so late
• surgat = gets up / is getting up

Together: why the brother gets up so late.

Tam sero means so late.

• tam = so
• sero = late

Here sero is an adverb, not an adjective. It describes the action surgat:

• surgat = gets up
• tam sero surgat = gets up so late

A learner might expect something like an adjective form, but in Latin sero is the normal adverb.

Enim means something like for, indeed, or you see.

It is a postpositive word, which means it usually comes second in its clause, not first. So Latin prefers:

• soror enim...

rather than putting enim at the very beginning.

In this sentence, it gives a reason or explanation for the speaker’s surprise:

• I do not know why my brother gets up so late; for my sister usually arrives at school first.

Because it depends on solet.

Soleo, solere means to be accustomed, to be in the habit of, or more naturally in English, to usually do something. It is commonly followed by an infinitive:

• venire solet = she usually comes / she is accustomed to come

So:

• soror... venire solet = the sister usually comes

More literally, is accustomed to come.

Solet is the 3rd person singular present of soleo.

Its basic sense is:

• is accustomed
• usually
• tends to

So venire solet can be translated in a few natural ways:

• she usually comes
• she is accustomed to come
• she tends to come

In this sentence, the idea is habitual action.

Prima agrees with soror, which is feminine singular nominative.

• soror = feminine singular nominative
• prima = feminine singular nominative

It means first, and it is used predicatively: the sister comes first.

So:

• soror prima venire solet = the sister usually comes first

It is not directly modifying scholam. It goes with soror.

Here it means first in the sense of arriving before others.

So prima venire means:

• to come first
• to arrive first

It is not just identifying her as the first sister or the first one in a list. The context is about who gets to school earliest.

Ad with the accusative often means to or toward a place.

So:

• ad scholam = to school

This expresses motion toward the school. Since venire involves coming, ad is very natural.

A learner might wonder whether Latin always omits a preposition as English sometimes does in go to school or come to school, but Latin often uses ad + accusative for this idea.

Latin often does not use possessive words like my, his, or her unless they are needed for emphasis or clarity.

So frater and soror by themselves can simply mean:

• brother
• sister

In context, they often mean his brother, my brother, her sister, and so on, depending on who is speaking and what has already been established.

Latin is often less explicit than English about possession when the relationship is obvious.

Nescio is present tense because the speaker is saying I do not know right now.

The sentence is framed from the speaker’s present point of view:

• Nescio = I do not know
• surgat = the verb inside the indirect question
• solet = usually / is accustomed

So the whole sentence describes a present lack of knowledge and a habitual contrast.

Yes. In this kind of sentence, that is exactly how it is often translated.

Because surgat is inside an indirect question, the subjunctive is required by Latin grammar, but English does not usually show that difference. So a natural translation is:

• I do not know why my brother gets up so late...

rather than something like may get up.

This is an important point: in indirect questions, the Latin subjunctive often has no special modal force in English.

The second half explains or supports the first.

• Nescio cur frater tam sero surgat = the speaker does not understand the brother’s late rising.
• soror enim ad scholam prima venire solet = after all, the sister usually gets to school first.

The idea seems to be that the brother’s lateness is surprising, especially when compared with the sister’s habit of arriving first. The semicolon helps mark this close but distinct relationship.

Yes: it is a very natural Latin way to express she usually comes first.

The structure is:

• prima = first
• venire = to come
• solet = usually does / is accustomed to do

So rather than using a separate adverb like usually and another phrase for arrives first, Latin simply says:

• prima venire solet

This is compact and idiomatic Latin.