Principium fabulae breve est.

Because fabulae means of the story. Latin often uses the genitive to show possession or close relationship, where English uses of or an apostrophe.

So:

• principium = beginning
• fabulae = of the story

Together, principium fabulae means the beginning of the story.

Principium is nominative singular. It is the subject of the sentence, the thing being described.

The sentence says that the beginning is brief, so principium is the word that goes with the verb est and the adjective breve.

Because it agrees with principium, which is a neuter singular noun.

In Latin, adjectives must agree with the nouns they describe in:

• gender
• number
• case

Since principium is neuter singular nominative, the adjective must also be neuter singular nominative: breve.

Latin often includes the verb est = is in this kind of sentence, just as English usually does.

So:

• Principium fabulae breve est = The beginning of the story is brief

In some contexts, Latin can leave out est if it is easy to understand, especially in poetry or very compressed style, but in normal prose it is often stated.

Classical Latin has no definite article like English the, and no indefinite article like a/an either.

So principium fabulae breve est can naturally mean:

• The beginning of the story is brief
• or, depending on context, A beginning of the story is brief

Usually the context tells you which English translation is best.

Yes. Latin word order is much freer than English word order because the endings show how the words function.

For example, these would mean essentially the same thing:

• Principium fabulae breve est
• Breve est principium fabulae
• Fabulae principium breve est

However, the chosen order can affect emphasis or style. The given sentence begins with principium, which puts focus first on the beginning.

Because of agreement.

• principium is nominative singular neuter
• breve is nominative singular neuter
• fabulae here is genitive singular feminine

Since breve matches principium in case, number, and gender, it describes principium, not fabulae.

Principium is a second-declension neuter noun.

Its nominative singular ends in -um, which is a very common sign of a second-declension neuter noun.

A few useful forms are:

• nominative singular: principium
• genitive singular: principii
• nominative plural: principia

Fabula is a first-declension noun.

Its genitive singular is fabulae, which is the form used here.

Some common forms are:

• nominative singular: fabula = story
• genitive singular: fabulae = of the story
• nominative plural: fabulae = stories

So fabulae can have more than one possible grammatical value in other sentences, but here it is clearly genitive singular because it depends on principium.

Yes. Brevis, breve is a third-declension adjective.

Its dictionary form is usually given as:

• brevis for masculine/feminine
• breve for neuter

That is why the neuter nominative singular here is breve, not something like brevum.

Yes. Est is a form of esse = to be, and here it links the subject to a description.

So the structure is:

• principium fabulae = subject
• breve = predicate adjective
• est = linking verb

In other words, the sentence does not show an action. It tells us what the subject is like.

A common classroom pronunciation would be roughly:

prin-KIP-ee-um fa-BU-lay BREH-way est

In reconstructed Classical pronunciation, v is pronounced like w, so breve sounds roughly like BREH-weh.

A careful Classical-style pronunciation would be approximately:

prin-KI-pi-um fa-BU-lae BRE-weh est

The exact pronunciation depends on whether you are using Classical or Ecclesiastical Latin.