Learn Hardcore Latin: Discipulus cum sua familia in urbe manet. - The student stays in the city with his family.

It is in the nominative singular form.
The ending -us is a typical nominative singular ending of a 2nd declension masculine noun.
The verb manet (he/she/it stays) is 3rd person singular, so its subject must also be singular. Discipulus matches that.

So: discipulus = the student (subject, nominative singular).

What case is familia, and why is it used that way with cum?

Familia is in the ablative singular.

The basic dictionary form is familia, familiae (1st declension).
Here it appears with the preposition cum.
Cum meaning with normally takes the ablative case.

So cum sua familia literally means with his/her own family, with familia in the ablative because it is the object of cum.

Why is it cum sua familia and not cum suam familiam?

Because cum requires the ablative case, not the accusative.

suam familiam would be accusative singular feminine, which would be used for a direct object, not after cum.
The correct ablative singular form of familia is familia (same spelling as nominative).
sua also changes form to agree with an ablative singular feminine noun.

So cum sua familia is the correct ablative phrase: with his/her own family.

What exactly does cum mean here? Can it ever mean when?

In this sentence, cum is a preposition meaning with.

It governs the ablative: cum sua familia = with his/her family.

Latin also has cum as a conjunction, meaning when, since, or although, but that usage:

Introduces a clause with a verb (e.g. cum venit = when he comes),
Not a simple noun phrase.

Here you have cum + noun in ablative, so it is clearly the preposition meaning with.

Why is it sua and not eius for his/her family?

Sua is used because it is the reflexive possessive adjective for the 3rd person.

sua means his own / her own / their own, referring back to the subject of the sentence.
eius means his / her, but refers to someone else, not the subject.

In this sentence, the subject is discipulus. So:

cum sua familia = with his (own) family (the family of the student).
If it were cum eius familia, it would mean with his/her family referring to some other person’s family, not the student’s.

So sua shows that the family belongs to the subject of the clause.

Why is sua feminine when discipulus is masculine?

Sua agrees in gender, number, and case with the noun it modifies, not with the owner.

The owner: discipulus (masculine singular).
The possessed thing: familia, which is feminine singular ablative.

So sua must also be:

feminine (to match familia),
singular (familia is singular),
ablative (because of cum).

Hence cum sua familia, not cum suus familia or anything similar.

What does in urbe literally mean, and what case is urbe?

In urbe literally means in the city.

urbs, urbis (f.) = city (3rd declension).
urbe is the ablative singular form.

With in, Latin uses:

in + ablative for location (in, on, at),
in + accusative for motion into (into, onto).

Here, in urbe describes where the student stays (location), so urbe is ablative.

Why is it in urbe manet instead of something like in urbe est?

Manet and est are different verbs:

manet (from manēre) = stays, remains, continues to be in a place.
est (from esse) = is (simply states existence or identity).

So:

in urbe manet = he/she stays in the city (idea of remaining there, not leaving).
in urbe est = he/she is in the city (a more neutral statement of location).

The chosen verb manet emphasizes staying / remaining rather than just being.

What person, number, and tense is manet, and how do I know?

Manet is:

3rd person
singular
present tense
indicative mood
active voice

You can tell because:

The stem is mane- from manēre (2nd conjugation).
The ending -t is the regular 3rd person singular present active ending in Latin.

So manet = he/she/it stays (or remains).

Why is the word order Discipulus cum sua familia in urbe manet? Could the words be rearranged?

Latin word order is fairly flexible because endings show grammatical roles.

The current order:

Discipulus (subject, fronted)
cum sua familia (with-phrase)
in urbe (place-phrase)
manet (verb at end, very typical in Latin)

You could also say, for example:

Discipulus in urbe cum sua familia manet.
In urbe discipulus cum sua familia manet.

All of these remain grammatical and keep the same basic meaning. The differences are mostly in emphasis or style, not in core meaning.

How would this sentence change if we were talking about students instead of a student?

You would make the subject and the possessive plural, and keep agreements:

Discipulus → Discipuli (nominative plural: students).
The verb manet must now be plural:
- manet → manent (they stay).
The family phrase could stay singular (each with his/their own family), or be made plural; usually singular makes sense here:
- cum sua familia can remain, with sua interpreted as their own (reflexive plural).

A natural plural version is:

Discipuli cum sua familia in urbe manent.
= The students stay in the city with their (own) family.

Does familia in Latin mean exactly the same as family in English?

Not exactly. Familia in Classical Latin most often means:

the household: people living under one roof and under one head of household,
often including slaves and other dependents,
not just parents and children.

In many textbook sentences, it is used in a modern, simplified sense like family, but historically its range is broader: household is often closer to the original idea.

Is discipulus specifically male? How would I say female student?

Yes, discipulus is grammatically masculine and usually means male student.

For a female student, you would use:

discipula (1st declension, feminine).

So the parallel sentence for a female student would be:

Discipula cum sua familia in urbe manet.

The rest of the sentence stays the same, because familia is already feminine and sua is agreeing with familia, not with the gender of the student.