Duae discipulae iam adsunt, sed ceterae adhuc absunt.

Because duae has to agree with discipulae, which is a feminine plural noun.

The numeral two in Latin is irregular:

• masculine: duo
• feminine: duae
• neuter: duo

Since discipula means a female student, the plural discipulae is feminine, so Latin uses duae discipulae = two female students.

They are nominative plural.

That is because they are the subjects of the verbs:

• duae discipulae ... adsunt = two students are present
• ceterae ... absunt = the others are absent

The verbs adsunt and absunt are both third person plural, so they go with plural subjects.

Yes, discipulae can be ambiguous when taken by itself. It can be:

• nominative plural = female students
• vocative plural
• genitive singular
• dative singular

But here it must be nominative plural, because:

• it is paired with duae
• the verb is adsunt, which is plural
• the sentence structure clearly needs a subject

So here discipulae means female students, not of the female student or to/for the female student.

They are forms of two compound verbs built from sum, esse (to be):

• adsum, adesse = to be present, to be here
• absum, abesse = to be absent, to be away

Their forms here are:

• adsunt = they are present
• absunt = they are absent

Both are present indicative active, third person plural.

You can think of them as related opposites:

• ad-
  • sum → being at or present
• ab-
  • sum → being away or absent

Latin certainly can say sunt praesentes or sunt absentes, but adsum and absum are very common verbs in their own right.

So instead of saying:

• they are present
• they are absent

Latin often simply uses:

• adsunt
• absunt

This is a very natural Latin way to express attendance or presence.

Because ceterae refers back to discipulae.

It means the others or the rest, but it is still grammatically agreeing with an understood feminine plural noun:

• ceterae = the other female students / the rest of the female students

So it is feminine plural nominative for the same reason duae is: it matches discipulae.

Because Latin often leaves out a noun when it is already obvious from the context.

So instead of saying:

• sed ceterae discipulae adhuc absunt

Latin can simply say:

• sed ceterae adhuc absunt

The meaning is still clear: the other students.

This is very common in Latin, especially when repeating the noun would be unnecessary.

They are adverbs of time:

• iam = already, by now
• adhuc = still, up to this point

So they create a nice contrast:

• duae discipulae iam adsunt = two students are already here
• sed ceterae adhuc absunt = but the others are still absent

Without those adverbs, the sentence would just state presence and absence. With them, it adds a sense of timing and expectation.

Yes, Latin word order is much more flexible than English word order.

This sentence is arranged very naturally:

• Duae discipulae — the first subject
• iam adsunt — what is true of them
• sed — contrast
• ceterae — contrasting subject
• adhuc absunt — what is true of them

The adverbs iam and adhuc are placed right before the verbs they modify, which is a common and clear arrangement.

Latin could rearrange the sentence for emphasis, but this version is straightforward and balanced.

It can mean either, depending on context. Here it means something like:

• the others
• the rest
• the remaining students

Since the sentence has already mentioned two students, ceterae naturally means all the other female students besides those two.

Because Latin does not have articles like English the or a/an.

So Latin simply says:

• duae discipulae
• ceterae

and context tells you whether English should use the, some, or no article at all.

For example:

• ceterae naturally becomes the others in English
• duae discipulae becomes two students

English needs articles more often than Latin does.

Yes. Sed is the standard Latin conjunction meaning but.

Here it links two contrasting statements:

• two students are already present
• but the others are still absent

It is a very common word and often introduces a simple contrast exactly like English but.