Margarita alba pretiosior est quam fibula argentea.

Because alba has to agree with margarita.

In Latin, adjectives agree with the nouns they describe in gender, number, and case.

• margarita is feminine singular nominative
• so the adjective must also be feminine singular nominative
• that gives alba

The other forms would be used with different kinds of nouns:

• albus = masculine singular nominative
• album = neuter singular nominative

So margarita alba means the white pearl.

Margarita is in the nominative singular.

You can tell because it is the subject of the sentence: it is the thing being described as more precious.

The verb is est = is, so the basic structure is:

• Margarita alba = the white pearl
• pretiosior est = is more precious

For a first-declension noun like margarita, the nominative singular often ends in -a.

Because pretiosior is the comparative form of the adjective pretiosus.

Latin often forms the comparative by adding -ior for masculine/feminine or -ius for neuter:

• pretiosus = precious
• pretiosior = more precious

Here it matches margarita, which is feminine, so pretiosior is the correct nominative singular form.

This is similar to English adjectives like:

• precious → more precious
• brave → braver

Latin uses a special adjective form instead of adding a separate word like more.

That is a very common question. Comparative adjectives work differently from regular first/second-declension adjectives.

A normal adjective like albus, alba, album has separate endings like:

• masculine: -us
• feminine: -a
• neuter: -um

But comparatives belong to a different pattern:

• masculine/feminine nominative singular: -ior
• neuter nominative singular: -ius

So:

• masculine: pretiosior
• feminine: pretiosior
• neuter: pretiosius

That is why the feminine subject margarita still takes pretiosior, not pretiosiora or pretiosiora.

Est is the third-person singular of esse, to be, and here it means is.

So the sentence literally includes:

• Margarita alba = the white pearl
• pretiosior est = is more precious

Latin sometimes can omit forms of to be, especially in poetry or very compressed style, but in normal straightforward prose it is very common to include est. In a learner sentence like this, using est makes the structure clear.

Quam means than in a comparison.

So:

• pretiosior est quam fibula argentea means
• is more precious than a silver brooch

The pattern is:

• comparative adjective + quam + second item

So Latin is doing exactly what English does in:

• more precious than ...

With quam, Latin normally puts the thing being compared in the same case as the first item.

Here:

• margarita alba is nominative
• so fibula argentea is also nominative

That gives:

• Margarita alba pretiosior est quam fibula argentea.

Literally:

• The white pearl is more precious than the silver brooch.

Latin also has another comparison construction, using the ablative without quam, but this sentence is not using that pattern.

Yes. Latin often uses the ablative of comparison instead.

So instead of:

• Margarita alba pretiosior est quam fibula argentea

you could have:

• Margarita alba fibulā argenteā pretiosior est

There the second item, fibulā argenteā, is in the ablative.

Both mean the same thing:

• The white pearl is more precious than the silver brooch

For beginners, the quam construction is often easier to recognize because it looks more like English.

Because argentea must agree with fibula.

• fibula is feminine singular nominative
• so the adjective describing it must also be feminine singular nominative
• therefore argentea

The forms would be:

• argenteus = masculine singular nominative
• argentea = feminine singular nominative
• argenteum = neuter singular nominative

So fibula argentea means the silver brooch.

Latin word order is much freer than English word order because the endings show the grammatical relationships.

This sentence is:

• Margarita alba pretiosior est quam fibula argentea

A very literal order is:

• Pearl white more-precious is than brooch silver

That sounds odd in English, but it is normal in Latin.

You could rearrange the Latin in various ways without changing the basic meaning, for example:

• Margarita alba quam fibula argentea pretiosior est
• Pretiosior est margarita alba quam fibula argentea

The endings, not the position, tell you what goes with what:

• margarita alba
• fibula argentea

You know from agreement.

Both adjective-noun pairs match in gender, number, and case:

• margarita
  • alba = feminine singular nominative
• fibula
  • argentea = feminine singular nominative

Since the adjectives match those nouns, they naturally belong together.

Word order can help, since they are next to each other here, but even if they were separated, the endings would still show the connection.

In standard textbook Latin, margarita commonly means pearl.

A learner might notice that some Latin words can have more than one meaning in different contexts, but in a sentence like this, especially with pretiosior and comparison to a silver brooch, pearl is the natural meaning.

So grammatically and contextually, margarita alba is best understood as the white pearl.

Latin has no definite or indefinite article like English the or a/an.

So:

• margarita can mean a pearl or the pearl
• fibula argentea can mean a silver brooch or the silver brooch

The context or the translation choice decides which sounds best in English.

That is why one Latin sentence can often be translated in more than one natural English way.