Postea mater fasciam albam mutat, quia vetus fascia humida est.

Because the word has two different jobs in the sentence.

• fasciam is the direct object of mutat: the mother changes the bandage. A direct object in Latin often takes the accusative case.
• fascia in vetus fascia humida est is the subject: the old bandage is wet. A subject is usually in the nominative case.

So:

• fascia = nominative singular
• fasciam = accusative singular

This is a very common pattern in Latin: the ending changes to show the word’s role.

Because albam describes fasciam, and adjectives in Latin must agree with the nouns they modify in:

• gender
• number
• case

Here, fasciam is:

• feminine
• singular
• accusative

So albam must also be:

• feminine
• singular
• accusative

That is why Latin says fasciam albam = a white bandage or the white bandage.

Because vetus is a third-declension adjective, and its nominative singular form is vetus for masculine, feminine, and neuter.

So with a feminine noun like fascia, you still say:

• vetus fascia = an old bandage

This is different from first/second-declension adjectives like albus, alba, album, which do change more obviously by gender.

Compare:

• alba fascia = white bandage
• vetus fascia = old bandage

Because it agrees with fascia, which is feminine.

In vetus fascia humida est, the adjective humida is a predicate adjective: it describes the subject after est.

Since fascia is:

• feminine
• singular
• nominative

humida must also be:

• feminine
• singular
• nominative

So humida est means is wet, with humida matching fascia.

Mutat comes from mutare, meaning to change.

Here it means something like:

• changes
• replaces

So mater fasciam albam mutat means the mother changes or replaces the white bandage.

Grammatically, mutat is:

• third person singular
• present tense
• active voice

So it means he/she/it changes. Because the subject is mater, we understand it as the mother changes.

Classical Latin normally does not have articles like English the and a/an.

So mater can mean:

• mother
• the mother
• sometimes a mother

And fasciam albam can mean:

• a white bandage
• the white bandage

You figure out which one is best from the context and the meaning already given.

This is something English speakers often have to get used to: Latin usually leaves definiteness unstated.

Postea means afterward, later, or after that.

It is an adverb, so it modifies the whole action:

• Postea mater fasciam albam mutat = Afterward, the mother changes the white bandage.

It helps show the sequence of events.

Because quia means because and introduces a subordinate clause giving a reason.

So:

• quia vetus fascia humida est = because the old bandage is wet

The clause has its own subject and verb:

• fascia = subject
• est = verb

In basic sentences like this, quia is commonly followed by the indicative, because it gives a straightforward reason.

Yes, Latin word order is more flexible than English because the endings show the grammar.

This sentence uses a very natural and clear order:

• fasciam albam = noun + adjective
• vetus fascia humida est = adjective + noun + adjective + verb

But Latin could rearrange some of this without changing the basic meaning, for example:

• mater albam fasciam mutat
• quia fascia vetus humida est

The exact order can affect emphasis or style, but the case endings still tell you what belongs together.

Because Latin often places the verb later in the clause, especially the verb to be.

So:

• vetus fascia humida est

is a very normal Latin order for:

• the old bandage is wet

Latin often likes to place the verb at or near the end, though this is not an absolute rule.

Yes. Mater is the subject of mutat.

Latin usually does not need a separate subject pronoun if the verb ending already tells you the person and number. Here mutat means he/she/it changes, and mater tells you exactly who that she is.

So Latin does not need to say:

• ea mutat = she changes

unless it wants extra emphasis.

You know from both meaning and grammar.

In the clause quia vetus fascia humida est:

• fascia is nominative singular feminine
• vetus can be nominative singular feminine
• humida is also nominative singular feminine

So both adjectives describe fascia.

Also, semantically it makes sense:

• the old bandage is wet

Latin often places adjectives near the noun they describe, but even if the order changes, agreement helps you match them correctly.

Here are the main forms:

• mater – third declension noun
• fascia – first declension noun
• albam / humida – from albus, alba, album, a first/second-declension adjective
• vetus – third-declension adjective
• mutat – verb from mutare
• est – verb from esse
• postea and quia – indeclinable words

This sentence is useful because it mixes several very common patterns in one short example.