Frater discipulum stultum vocat, quia rumorem falsum credit.

Because frater is in the nominative singular, the case usually used for the subject of a sentence.

• frater = the brother
• It is the person doing the action of vocat and credit

So frater is the one who calls and believes.

Because discipulum is the direct object of vocat.

The verb vocare here means to call someone something, and the person being called is put in the accusative:

• discipulum = the student / pupil
• accusative singular of discipulus

So the brother is calling the student something.

Because with verbs like vocare, Latin often puts both:

1. the person being called, and
2. the name or description given to that person

in the accusative.

So:

• discipulum = the student
• stultum = foolish / stupid

Together, discipulum stultum vocat means he calls the student foolish or he calls the student a fool.

This is sometimes called a double accusative construction with vocare.

Because stultum agrees with discipulum.

Latin adjectives must match the nouns they describe in:

• gender
• number
• case

Here:

• discipulum is masculine singular accusative
• so stultum must also be masculine singular accusative

That is why it is stultum, not stultus.

Vocat is the 3rd person singular present active indicative of vocare.

So it means:

• he calls
• she calls
• it calls

Since the subject is frater, here it means the brother calls.

In this sentence, vocare does not mean to summon so much as to call someone by a name / label.

Because Latin usually does not need a subject pronoun when the verb ending already shows the person and number.

• vocat = he/she/it calls
• credit = he/she/it believes

Since frater is already named as the subject, Latin does not need is for he.

Rumorem is accusative singular because it is the direct object of credit.

• rumor = rumor / report
• rumorem = accusative singular

The brother believes a false rumor, so rumorem is the thing believed.

Because falsum describes rumorem, so it must agree with it.

• rumorem = masculine singular accusative
• falsum = masculine singular accusative

So rumorem falsum means a false rumor.

Quia means because and introduces a subordinate clause giving the reason.

So the structure is:

• Frater discipulum stultum vocat = main clause
• quia rumorem falsum credit = reason clause

Together: the brother calls the student foolish because he believes a false rumor.

The most natural subject is still frater.

Latin often leaves the subject unstated in a subordinate clause if it is the same as the subject of the main clause.

So the understood meaning is:

• The brother calls the student foolish, because the brother believes a false rumor.

If Latin wanted to make a different subject especially clear, it could name that subject explicitly.

Yes. Latin word order is much freer than English word order because the case endings show each word’s role.

For example, these would mean the same basic thing:

• Frater discipulum stultum vocat
• Discipulum frater stultum vocat
• Stultum discipulum frater vocat

The author’s chosen order may give emphasis or sound more natural in context, but the endings still show:

• frater = subject
• discipulum = object
• stultum = description of the object

Because rumor, rumoris is a masculine third-declension noun.

That is why its adjective is masculine too:

• rumorem falsum

A learner cannot always guess a noun’s gender from its meaning, so this usually has to be learned from the dictionary entry.

Both are present tense.

• vocat = calls
• credit = believes

So the sentence describes a present or general action:

• The brother calls the student foolish because he believes a false rumor.

Depending on context, English might sometimes translate this more naturally as a general truth or habitual action.

Grammatically, it is an adjective agreeing with discipulum.

But in translation, English may express the idea either as:

• foolish
• stupid
• or even a fool

So Latin uses an adjective, while English may use either an adjective or a noun depending on style.

You would look them up as:

• frater, fratris = brother
• discipulus, discipuli = student, pupil
• stultus, -a, -um = foolish, stupid
• voco, vocare, vocavi, vocatus = call
• quia = because
• rumor, rumoris = rumor, report
• falsus, -a, -um = false
• credo, credere, credidi, creditus = believe

This helps you identify the declension or conjugation and understand the forms used in the sentence.