Discipuli libros secum habent.

Here discipuli is nominative plural, so it is the subject of the sentence: the students.

A beginner may notice that discipuli can also be genitive singular of discipulus in other contexts, meaning of the student. But in this sentence it must be nominative plural, because the verb habent is plural and needs a plural subject.

Libros is accusative plural of liber, meaning books.

It is in the accusative because it is the direct object of habent: the students have books. In Latin, the direct object is usually put in the accusative case.

So:

• liber = book
• libros = books, as the object of the verb

Because the subject discipuli is plural.

• habet = he/she/it has
• habent = they have

Latin verbs change their endings to show who is doing the action. Since discipuli means the students, the verb must be plural: habent.

Secum means with themselves or, more naturally in English here, with them.

It is made from:

• se = themselves / himself / herself as a reflexive pronoun
• cum = with

But with these pronouns, Latin usually combines them into a single word:

• mecum = with me
• tecum = with you
• secum = with himself / herself / themselves
• nobiscum = with us
• vobiscum = with you all

So secum habent means they have the books with them.

Because that is the normal Latin pattern with these pronouns.

Instead of putting cum before the pronoun, Latin usually attaches it after:

• not usually cum me, but mecum
• not usually cum te, but tecum
• not usually cum se, but secum

So secum is simply the standard idiomatic Latin form.

Because se is reflexive: it refers back to the subject of the clause.

In this sentence, the subject is discipuli, so secum means with themselves / with them, referring back to the students.

If Latin wanted to say with them meaning some other people, not the subject, it would use a non-reflexive form such as cum eis.

So the difference is:

• secum = with themselves, referring back to the subject
• cum eis = with them, referring to someone else

The sentence is understandable because of the endings, not just the word order.

So Discipuli libros secum habent is a normal way to say it, but Latin could also say things like:

• Libros discipuli secum habent
• Secum discipuli libros habent

The basic meaning would stay the same, because:

• discipuli is still nominative plural
• libros is still accusative plural
• habent is still plural
• secum still refers back to the subject

That said, different word orders can give different emphasis.

Because Latin has no articles like English the or a/an.

So discipuli can mean:

• students
• the students

And libros can mean:

• books
• the books

The exact sense depends on context. In many textbook translations, English uses the because it sounds more natural.

By itself, the sentence simply says that the students have books with them.

It does not necessarily mean that each student has their own separate books. It just tells you that the students, as the subject, are in possession of books and have those books with them.

So the sentence gives the general idea of accompaniment, not a precise distribution of ownership.

It would become:

Discipulus librum secum habet.

That means The student has a book with him/her.

Notice the changes:

• discipuli → discipulus for a singular subject
• libros → librum for a singular object
• habent → habet for a singular verb

Secum stays the same form, though in translation it would now mean with himself/herself depending on context.