Cum titulus nimis longus esset, magister eum breviorem facere iussit.

Here cum introduces a subordinate clause: Cum titulus nimis longus esset.

In this sentence, cum is best understood as when or since/because, depending on context. In school Latin, this is often called a circumstantial or causal cum clause.

Because the verb in the clause is subjunctive (esset), this is not the simple cum = when construction that takes the indicative in very straightforward time expressions. Instead, it gives background circumstance:

• Cum titulus nimis longus esset = since/when the title was too long

So cum here sets the scene for the main action.

Because after this kind of cum clause, Latin normally uses the subjunctive.

So:

• erat would be indicative
• esset is imperfect subjunctive

The subjunctive here does not necessarily make the statement doubtful. It is simply the normal grammar after cum in a clause giving background, cause, or circumstance.

So:

• cum ... esset = when/since ... was
• not because the title might have been too long, but because Latin regularly uses the subjunctive in this construction

It is imperfect because it is describing a past situation that was going on at the time of the main verb.

The main verb is iussit = ordered, which is perfect tense, referring to a completed past action. The cum clause gives the background situation at that time:

• Cum titulus nimis longus esset = Since/When the title was too long
• magister eum breviorem facere iussit = the teacher ordered him/it to make it shorter

So the imperfect subjunctive shows an ongoing or existing state in past time: the title was too long at the time the teacher gave the order.

Titulus is nominative singular.

It is the subject of esset, because the clause means the title was too long.

You can see the structure like this:

• titulus = subject
• nimis longus = predicate adjective phrase describing the subject
• esset = was

So titulus has to be nominative because it is the thing that was too long.

Nimis means too, excessively, or overly.

It modifies the adjective longus:

• longus = long
• nimis longus = too long

So nimis is an adverb telling you the degree of the adjective. It does not agree with anything, because adverbs do not change form for case, number, or gender.

Eum is accusative because it is the direct object of iussit.

The teacher ordered him or it:

• magister = the teacher
• eum = him/it
• iussit = ordered

So the pattern is:

• someone
  • someone (accusative) + infinitive
• magister eum facere iussit = the teacher ordered him/it to do

In context, eum most naturally refers back to titulus, so it means it, not him.

Latin often uses a pronoun instead of repeating the noun, just as English does.

So after titulus has already been mentioned, Latin can say eum = it.

That helps avoid repetition:

• Cum titulus nimis longus esset, magister eum...
• Since the title was too long, the teacher ordered it...

Because titulus is masculine singular, the pronoun referring back to it is also masculine singular: eum.

Breviorem is accusative singular masculine because it agrees with eum.

Here it functions as a predicate accusative with facere:

• eum breviorem facere = to make it shorter

This is a common Latin pattern:

• object in accusative
• adjective in accusative agreeing with that object
• infinitive facere

Compare the idea in English:

• to make the title shorter

Latin expresses that as:

• titulum breviorem facere

So breviorem matches eum in case, number, and gender:

• accusative
• singular
• masculine

Because breviorem is agreeing with a masculine noun/pronoun, eum.

Brevis is the adjective short. Its comparative is:

• masculine/feminine accusative singular: breviorem
• neuter accusative singular: brevius

Since titulus is masculine, the pronoun referring to it is masculine (eum), and the comparative adjective must also be masculine accusative singular:

• eum breviorem facere

If the noun were neuter, you would expect brevius instead.

After iubere (to order), Latin commonly uses an accusative + infinitive construction.

So:

• magister eum breviorem facere iussit
• literally: the teacher ordered him/it to make it shorter

The structure is:

• magister = subject
• eum = person/thing ordered
• breviorem facere = infinitive phrase expressing what was ordered
• iussit = ordered

This is different from English, which often uses to:

• ordered it to become shorter
• ordered him to make it shorter
• or more naturally in context, ordered that it be made shorter

Latin prefers the infinitive construction here.

Because iubere usually does not take ut in classical Latin. Instead, it normally takes the accusative + infinitive construction.

So Latin says:

• magister eum breviorem facere iussit

rather than:

• magister iussit ut...

A native English speaker may expect something like ordered that..., but Latin often handles this more directly with an object plus an infinitive.

So this is a very standard construction:

• iubeo + accusative + infinitive

A fairly literal unpacking would be:

• Cum = when/since
• titulus = the title
• nimis longus = too long
• esset = was
• magister = the teacher
• eum = it
• breviorem = shorter
• facere = to make
• iussit = ordered

So, almost word-for-word:

When/Since the title was too long, the teacher ordered it to make shorter

That sounds awkward in English, but it helps show the Latin structure. Better English would be something like:

Since the title was too long, the teacher ordered it to be made shorter or Since the title was too long, the teacher ordered them to shorten it

It means make it shorter.

The pronoun eum refers back to titulus, so it is the thing being made shorter. There is no reflexive pronoun here, so the sense is not make himself shorter.

Grammatically:

• eum = the object being changed
• breviorem = the new state of that object
• facere = to make

So the phrase means:

• to make it shorter

A learner should probably notice these:

1. Cum introduces a subordinate clause.
2. That cum clause uses the subjunctive: esset.
3. Titulus is nominative because it is the subject of esset.
4. Nimis is an adverb meaning too.
5. Eum is accusative because it is the object of iussit and refers back to titulus.
6. Breviorem is a comparative adjective agreeing with eum.
7. Iussit takes an accusative + infinitive construction: eum breviorem facere.

So this one sentence is a good example of several very common Latin patterns at once.